CN105897643B - Based on joint narrowband Interference Detection, elimination and the channel estimation methods of continuous cyclic shift training sequence in ofdm system - Google Patents

Based on joint narrowband Interference Detection, elimination and the channel estimation methods of continuous cyclic shift training sequence in ofdm system Download PDF

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CN105897643B
CN105897643B CN201610215401.8A CN201610215401A CN105897643B CN 105897643 B CN105897643 B CN 105897643B CN 201610215401 A CN201610215401 A CN 201610215401A CN 105897643 B CN105897643 B CN 105897643B
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interference
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CN105897643A (en
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张晓瀛
魏急波
马东堂
吴宇
王欣
王桁瑶
黄卫英
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National University of Defense Technology
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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
    • H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
    • H04L27/2691—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation involving interference determination or cancellation
    • 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
    • H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
    • H04L27/2695—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation with channel estimation, e.g. determination of delay spread, derivative or peak tracking

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
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Abstract

The present invention relates in a kind of ofdm system based on joint narrowband Interference Detection, elimination and the channel estimation methods of continuous cyclic shift training sequence.This method is in the case where carrying out channel estimation using two OFDM symbol training sequences, asynchronous narrowband Interference Detection, estimation, elimination are realized using signal detection and estimation technology and training sequence designing technique, applied in the ofdm systems such as the WLAN IEEE 802.11a or wireless MAN WiMAX IEEE 802.16e interfered there are narrowband, it is realizing the accurate estimation and elimination for realizing asynchronous narrow-band interference signal while interference robust detection, is effectively promoting the performance of training sequence assisted channel estimation under disturbed condition.

Description

Interfere inspection in joint narrowband in ofdm system based on continuous cyclic shift training sequence Survey, elimination and channel estimation methods
Technical field
The present invention relates to the channel estimation methods of anti-narrowband interference a kind of in ofdm system, it particularly relates to a kind of benefit Joint narrowband Interference Detection, estimation, elimination and channel are realized with two OFDM training symbols with continuous cyclic shift characteristic The method of estimation
Background technique
With the explosive growth of wireless service, frequency spectrum becomes precious resource.Multiple communication services are allowed to share Frequency spectrum is one of the feasible program for solving spectrum congestion.Currently, in ISM (Industrial-Scientific-Medical) etc. For unauthorized frequency range, a variety of communication systems, which coexist, has become reality.When narrowband systems and based on the wide-band communication system of OFDM When coexisting, narrowband interference becomes receiver and designs major issue in need of consideration, although cognitive radio technology can pass through frequency Interference is evaded in spectrum perception, but there is always certain false dismissal probabilities, interference to avoid completely for frequency spectrum detection in reality.Narrowband Interference can be divided into interference intentionally and be not intended to two classes of interference.In terms of being not intended to interference, the digital television broadcasting based on OFDM technology System will receive narrowband caused by simulated television, ham radio signal and receiver intermodulation and interfere；Based on WLAN The system of IEEE 802.11a/n communication standard will receive the influence of the narrowbands such as bluetooth, micro-wave oven signal interference.It is interfering intentionally Aspect, narrowband interference is one of the military channels important jamming signal type in need of consideration based on OFDM technology.Channel estimation It is the basis of OFDM coherent demodulation, precision of channel estimation has important influence to system performance.Current existing communication standard The channel estimation methods based on training sequence are mostly used, such as WLAN standard IEEE 802.11a, wireless MAN WiMAX standard IEEE 802.16e etc. passes through conventional method when the training sequence that receiver receives is interfered by narrowband to be polluted Estimate that obtained channel coefficients can no longer represent channel state information, it is therefore desirable to carry out narrowband Interference Estimation and elimination.
Current existing narrowband disturbance suppression and elimination problem are segmented into two classes: 1) frequency domain method；2) time domain approach.? Some frequency domain methods by setting threshold value to narrowband interference detected and eliminated, or using compressed sensing algorithm to interfere into Row estimation and elimination, these methods are to there are the asynchronous narrowbands of frequency shift (FS) to interfere shortage robustness；Time domain approach passes through first Time domain linear filter positions interference, then filters out interference using notch filter, and such methods convergence is slowly, smart It spends not high.Therefore, existing result of study can only perhaps handle synchronous narrow-band interference or be unable to the interference of accurate reconstruction narrowband, There is biggish limitation in performance.Not yet discovery is instructed there are under asynchronous Narrowband Jamming using ofdm system channel estimation Practice sequence and carries out joint narrowband Interference Detection, the data of elimination and channel estimation.
Summary of the invention
Technical problem to be solved by the invention is to provide one kind to carry out channel using two OFDM symbol training sequences In the case where estimation, using signal detection and estimation technology and training sequence designing technique realize asynchronous narrowband Interference Detection, Estimation, the method eliminated, applied to the WLAN IEEE 802.11a or wireless MAN WiMAX interfered there are narrowband In the ofdm systems such as IEEE 802.16e, accurately estimating for asynchronous narrow-band interference signal is realized while interference robust detection realizing Meter and elimination, effectively promote the performance of training sequence assisted channel estimation under disturbed condition.
In order to solve the above-mentioned technical problem, the invention proposes joint narrowband Interference Detection, estimation, elimination and channels to estimate The design scheme of meter.The program specifically includes that 1) design has the two symbol CP-OFDM training sequence of continuous cyclic shift characteristic Column；2) detection is compared using the Robust Statistics amount C of design and threshold value T, judges whether there is narrowband interference；If 3) detect There are narrowband interference, since first OFDM symbol data part, are equal to cyclic prefix with length, spacing is sub-carrier number N Three segment datas estimate the score overtones band offset of asynchronous narrowband interference；4) accordingly and the using first OFDM symbol number Two OFDM symbol cyclic prefix start the data symbol that length is sub-carrier number N and do difference, estimate narrowband interference integral multiple The equivalent signal of sub-carrier frequencies position；5) the score overtones band offset and step 4) estimated using step 3) is estimated Integral multiple sub-carrier frequencies at equivalent signal reconstruct narrowband interfere time-domain signal, carry out time domain interference eliminate, obtain interference disappear Training sequence after removing receives signal.6) training sequence after being eliminated using interference is received signal or by step 2) detection judgement The training sequence of no narrowband interference receives signal and carries out channel estimation.
The technical scheme is that devising a kind of joint narrowband interference inspection based on continuous cyclic shift training sequence It surveys, elimination and channel estimation methods have applied in the CP-OFDM system scenarios interfered there may be either synchronously or asynchronously narrowband Body includes the following steps:
Assuming that a CP-OFDM system has N number of subcarrier；Cyclic prefix (CP, cyclic Prefix) length is LCP；Hair The training sequence signal power penetrated is normalized to 1, and narrow-band interference signal power is PJ；Time domain wireless multi-path channels are denoted as h=[h0 h1…hL-1]T, it is assumed that LCP> L；Additive white Gaussian noise variance is σ2；Define interference noise power ratio (INR, Interference to Noise Ratio)
Step 1), design have two symbol training sequences of continuous cyclic shift characteristic
The frequency domain of first OFDM training sequence symbols is sent into signal and is denoted as X1=[X1,0 X1,1…X1,N-1]T, wherein Xi ∈{±1,±j}.It is X that the frequency domain of second OFDM training sequence symbols, which sends signal,2=[X2,0 X2,1…X2,N-1]T, then
Wherein Φ is the diagonal matrix of N × N, X2I-th of element meet0≤i≤N-1.Two The corresponding time-domain signal of symbol training sequence is respectively x1=FHX1, x2=FHX2, wherein FHIndicate IFFT unitary matrix.By each training The end L of symbolCPA symbol copies to before symbol and forms cyclic prefix, then is formed by time-domain training sequence and has and continuously follow Ring shift characteristics:
Wherein
Step 2) compares detection using the Robust Statistics amount C and threshold value T of design, judges whether there is narrowband interference.
2.1 calculate the decision statistics C of narrowband Interference Detection
Assuming that channel is constant when keeping within two OFDM training sequence times, then time-domain training sequenceBy channel it Reception signal y afterwards can be indicated are as follows:
WhereinIndicate convolution；For 1 × (2N+2LCP+ L-1) time domain Receive signal.Time domain is taken to send the reception signal that signal [Seg2 Seg3 Seg1] corresponding two segment length is N
Calculate the difference signal Δ y of two segment signals:
Δ y=y2-y1
Then decision statistics C are as follows:
C=max (| FHΔy|) (3)
Wherein max (A) indicates to take the maximum value of vector element.
2.2 calculate decision threshold according to (4) formula:
T=α × Med (| FHΔy|) (4)
Wherein Med (A) indicates to take the median of vector element.
WhereinExpression rounds up,KmaxIndicate the maximum degree of rarefication of narrowband interference, INRminExpression system least interference noise ratio in need of consideration when designing.If C > T, there are narrowband interference for judgement；If C≤T, Then judge no narrowband interference.
If step 3) detects the presence of narrowband interference, since first OFDM symbol data part, it is equal to length and is followed Ring prefix, spacing are the score overtones band offset that three segment datas of sub-carrier number N estimate asynchronous narrowband interference.It is specific to execute Steps are as follows:
3.1 take out three segment length as LCPReception signal S1,S2,S3:
The part that the corresponding transmitting signal of this three segment signal is Seg2.
3.2 estimate the score overtones band offset of asynchronous narrowband interference according to (7) formula:
Wherein Angle [A] indicates to seek the angle of plural number,Indicate the score overtones band bias estimation value that estimation obtains.
Step 4), using first OFDM symbol number accordingly and second OFDM symbol cyclic prefix start length for son carry The data symbol of wave number N does difference, estimates the equivalent signal of narrowband interference integral multiple sub-carrier frequencies position；
The 4.1 score overtones band offset estimated values obtained using step 3)Calculating observation matrix Ψ:
First OFDM symbol number being computed be accordingly and second OFDM symbol cyclic prefix in 4.2 taking-up steps 2) The difference signal Δ y for starting the data symbol that length is sub-carrier number N obtains narrowband using least-squares algorithm and interferes integral multiple The initial estimation of sub-carrier frequencies position equivalent signal
At the 4.3 sparsity further progress filtering using narrowband interference integral multiple sub-carrier frequencies position equivalent signal Reason.It is rightEach element is ranked up, and is usedIndicate sequenceThe preceding L of the larger valueCPThe sequence of a element Number set, takes out in observing matrix by the corresponding each column of set Sup, updates narrowband interference integral multiple subcarrier frequently according to (10) formula The estimated value of rate position equivalent signal:
The integer gall nut that step 5), the score overtones band offset estimated using step 3) and step 4) are estimated carries Equivalent signal reconstruct narrowband interferes time-domain signal at wave frequency rate, carries out time domain interference and eliminates, obtains the training sequence after interference is eliminated Column receive signal.
5.1, R is interfered according to the time-domain narrowband that (11) and (12) formula reconstruct first OFDM symbol data part1With second The time-domain narrowband of a OFDM symbol data part interferes R2:
WhereinDiag (A) table Show using independent variable vector element as the diagonal matrix of diagonal entry.
5.2, narrow-band interference excision is carried out to the training sequence time-domain signal received, obtains the reception letter after interference is eliminated Number
Step 6) receives signal using the training sequence after interference elimination or judges that no narrowband interferes by step 2) detection Training sequence receive signal carry out channel estimation；
If 6.1, judging no narrowband interference by step 2), directly utilizeWithEstimate channel；If sentencing Disconnected there are narrowband interference, then utilize the reception signal after narrow-band interference excisionWithEstimate channel；
6.2, the channel frequency response on subcarrier is sought according to least square method, and is taken in two OFDM symbols Value；
6.3, channel frequency response is subjected to inverse-Fourier transform to time domain, retains L before gained time-domain coefficientsCPA system Number, by rear N-LCPA coefficient is set to zero, then by Fourier transform to frequency domain, obtains channel frequency response estimated value
Beneficial effects of the present invention
Joint narrowband Interference Detection, elimination and channel estimation proposed by the present invention based on continuous cyclic shift training sequence Method, applied to interfered there may be narrowband WLAN IEEE 802.11a system, wireless MAN IEEE In the wideband OFDM systems such as 802.16d, the presence or absence of narrowband interference can be accurately detected, and there are the items that asynchronous narrowband interferes Under part can equivalent signal at estimated score overtones band offset and integral multiple sub-carrier frequencies simultaneously, when realizing narrowband interference The accurate estimation and elimination of domain signal farthest reduce influence of the narrowband interference to channel estimation quality.This method can Intentional or unintentional narrowband interference is effectively eliminated, the performance of wideband OFDM communication system is improved.
Detailed description of the invention
Fig. 1 is the flow chart provided by the invention for combining narrowband Interference Detection, elimination and channel estimation methods；
Fig. 2 is to compare design method of the present invention and other methods just under the conditions of different narrow band interference noise power ratio True detection probability；
Fig. 3 is to compare the letter of design method and other methods of the present invention under the conditions of different narrow band interference noise power ratio Estimate mean square error performance in road；
Fig. 4 is the channel of comparison design method and other methods of the present invention under the conditions of the different signal-to-noise ratio of no narrowband interference Estimate mean square error performance；
Fig. 5 is to compare design method and its other party of the present invention under the conditions of setting the different signal-to-noise ratio of certain narrowband interference The channel estimation mean square error performance of method.
Specific embodiment
The present invention will be further explained below with reference to the attached drawings.
Fig. 1 is the flow chart provided by the invention for combining narrowband Interference Detection, elimination and channel estimation methods.Such as Fig. 1 institute Show, method includes the following steps:
Step 1), design have two symbol training sequences of continuous cyclic shift characteristic
Step 2) compares detection using the Robust Statistics amount C and threshold value T of design, judges whether there is narrowband interference.
2.1, the decision statistics C of narrowband Interference Detection is calculated
2.2, decision threshold T is calculated according to (4) formula, if C > T, there are narrowband interference for judgement；If C≤T judges nothing Narrowband interference.
If step 3) detects the presence of narrowband interference, since first OFDM symbol data part, it is equal to length and is followed Ring prefix, spacing are the score overtones band offset that three segment datas of sub-carrier number N estimate asynchronous narrowband interference.It is specific to execute Steps are as follows:
3.1, taking out three segment length is LCPReception signal；
3.2, the score overtones band offset of asynchronous narrowband interference is estimated according to (7) formula
Step 4), using first OFDM symbol number accordingly and second OFDM symbol cyclic prefix start length for son carry The data symbol of wave number N does difference, estimates the equivalent signal of narrowband interference integral multiple sub-carrier frequencies position；
4.1, the score overtones band offset estimated value obtained using step 3)Calculating observation matrix Ψ:
4.2, first OFDM symbol number being computed in step 2) is taken out accordingly and before second OFDM symbol circulation Sew the difference signal Δ y for starting the data symbol that length is sub-carrier number N, obtains narrowband using least-squares algorithm and interfere integer The initial estimation of times sub-carrier frequencies position equivalent signal
4.3, at the sparsity further progress filtering using narrowband interference integral multiple sub-carrier frequencies position equivalent signal Reason.It is rightEach element is ranked up, and is usedIndicate sequenceThe preceding L of the larger valueCPA element Serial number set is taken out in observing matrix by the corresponding each column of set Sup, updates narrowband according to (10) formula and interfere integral multiple subcarrier The estimated value of frequency location equivalent signal:
The integer gall nut that step 5), the score overtones band offset estimated using step 3) and step 4) are estimated carries Equivalent signal reconstruct narrowband interferes time-domain signal at wave frequency rate, carries out time domain interference and eliminates, obtains the training sequence after interference is eliminated Column receive signal.
5.1, it is interfered according to the time-domain narrowband that (11) and (12) formula reconstruct two OFDM symbol data parts；
5.2, narrow-band interference excision is carried out to the training sequence time-domain signal received, obtains the reception letter after interference is eliminated Number
Step 6) receives signal or the training sequence reception signal without narrowband interference using the training sequence after interference elimination Carry out channel estimation；
If 6.1, judging no narrowband interference by step 2), channel directly is estimated using reception signal；If judgement exists Narrowband interference, then estimate channel using the reception signal after narrow-band interference excision；
6.2, the channel frequency response on subcarrier is sought according to least square method, and is taken in two OFDM symbols Value；
6.3, channel frequency response is subjected to inverse-Fourier transform to time domain, retains L before gained time-domain coefficientsCPA system Number, by rear N-LCPA coefficient is set to zero, then by Fourier transform to frequency domain, obtains channel frequency response estimated value.
Fig. 2, Fig. 3, Fig. 4, Fig. 5 are joint narrowband Interference Detections, the property of elimination and channel estimation methods proposed by the present invention It can simulation curve figure.Here narrowband interference number is represented with the occupied integral multiple sub-carrier frequencies number of narrowband interference.Emulation ginseng Number setting are as follows: N=64, LCP=16, channel length L=8.
As shown in Fig. 2, abscissa indicates narrowband interference and additive white Gaussian noise power ratio INR；Ordinate indicates different Algorithm sets Signal to Noise Ratio (SNR)=12dB, it is 6 that narrowband, which interferes number, for the correct probability of narrowband Interference Detection in simulations.Figure Rectangular mark curve is the correct detection probability curve for the narrowband Interference Detection algorithm that the present invention designs in 2；Triangle mark is bent Line indicates that the energy detection method designed in document [1] carries out the correct detection probability of narrowband Interference Detection.It can from Fig. 2 Out, it is 1 that the narrowband Interference Detection algorithm that the present invention designs, which only needs INR >=12dB to be just able to satisfy accurate detection probability,.
As shown in figure 3, abscissa indicates narrowband interference and additive white Gaussian noise power ratio INR；Ordinate indicate according to The estimation mean square error performance of distinct methods progress channel estimation.Signal to Noise Ratio (SNR)=12dB, narrowband interference are set in simulations Number is 1, and narrowband interfering frequencies deviate ε=0.3.As can be seen from Figure 3: the design side of the invention indicated by rectangular mark curve The channel estimating performance of method is in close proximity to perfect channel estimation performance when known narrowband interference.And by circle markings curve table For the conventional method performance for not doing interference processing directly progress channel estimation shown as the promotion of INR deteriorates rapidly, performance is obvious It is inferior to inventive algorithm.In conclusion processing method proposed by the present invention is capable of providing the robust channel under Narrowband Jamming Estimation.
As shown in figure 4, abscissa indicates signal and additive white Gaussian noise power ratio, i.e. Signal to Noise Ratio (SNR)；Ordinate indicates The estimation mean square error performance of channel estimation is carried out according to distinct methods.No narrowband interference is assumed in simulations.It can from Fig. 4 To find out: the channel estimation mean square error performance of the design method of the present invention indicated by rectangular mark curve and known narrowband interfere Channel estimation method performance when state is identical, this has reacted this algorithm can effectively detect to interfere when there is no narrowband interferes Existence, will not degraded channel estimation performance when no narrowband interferes.In conclusion processing method proposed by the present invention exists Also it can guarantee the channel estimating performance of robust in the absence of interference by accurately detecting interference existence.
As shown in figure 5, abscissa indicates signal and additive white Gaussian noise power ratio, i.e. Signal to Noise Ratio (SNR)；Ordinate indicates The estimated error mean squares error performance of channel estimation is carried out according to distinct methods.INR=12dB in simulations, narrowband interfere number It is 6, narrowband interfering frequencies deviate ε=0.3.As can be seen from Figure 5: the design method of the present invention indicated by rectangular mark curve Perfect channel estimation algorithm performance when interfering of channel estimation mean square error performance and known narrowband it is close, be significantly better than tradition Channel estimation method performance and the channel estimation method performance indicated by triangle mark curve.In conclusion the present invention proposes Processing method can guarantee that there are the performances of channel estimation when narrowband interference.

Claims (5)

  1. Based on joint narrowband Interference Detection, elimination and the channel estimation side of continuous cyclic shift training sequence in 1.OFDM system Method is carried out channel estimation using two OFDM symbol training sequences, is set using signal detection and estimation technology and training sequence Meter technology realizes asynchronous narrowband Interference Detection, estimation, elimination, which comprises the steps of:
    Step 1, design have two symbol CP-OFDM training sequences of continuous cyclic shift characteristic；
    Step 2 compares detection using the Robust Statistics amount C and threshold value T of design, judges whether there is narrowband interference；
    If step 3 detects the presence of narrowband interference, since first OFDM symbol data part, before being equal to circulation with length Sew, spacing is the score overtones band offset that three segment datas of sub-carrier number N estimate asynchronous narrowband interference；
    Step 3 specifically:
    If 3.1 detect the presence of interference by step 2, three segment length of taking-up are circulating prefix-length LCPReception signal S1,S2, S3:
    The part that the corresponding transmitting signal of this three segment signal is Seg2,
    3.2 estimate the score overtones band offset of asynchronous narrowband interference according to (7) formula:
    WhereinIndicate to ask plural angle,Indicate the score overtones band bias estimation value that estimation obtains；
    Step 4, using first OFDM symbol number accordingly and second OFDM symbol cyclic prefix start length be sub-carrier number N Data symbol do difference, estimate narrowband interference integral multiple sub-carrier frequencies position equivalent signal；
    Step 4 specifically:
    The 4.1 score overtones band offset estimated values obtained using step 3Calculating observation matrix Ψ:
    Wherein FHIndicate IFFT unitary matrix；
    First OFDM symbol number being computed in 4.2 taking-up steps 2 is accordingly and second OFDM symbol cyclic prefix starts Length is the difference signal Δ y of the data symbol of sub-carrier number N, obtains narrowband interference integer gall nut using least-squares algorithm and carries The initial estimation of wave frequency rate position equivalent signal
    4.3 are filtered using the sparsity further progress of narrowband interference integral multiple sub-carrier frequencies position equivalent signal, right Each element is ranked up, and is usedIndicate sequenceThe preceding L of the larger valueCPThe serial number collection of a element It closes, takes out in observing matrix by the corresponding each column of set Sup, update narrowband according to (10) formula and interfere integral multiple sub-carrier frequencies position Set the estimated value of equivalent signal:
    The integral multiple sub-carrier frequencies that step 5, the score overtones band offset estimated using step 3 and step 4 are estimated Locate equivalent signal reconstruct narrowband and interfere time-domain signal, carry out time domain interference and eliminate, obtains the training sequence after interference is eliminated and receive Signal；
    Step 6, the training for receiving signal using the training sequence after interference elimination or judging no narrowband interference by step 2 detection Sequential reception signal carries out channel estimation.
  2. 2. the joint narrowband in ofdm system according to claim 1 based on continuous cyclic shift training sequence interferes inspection Survey, elimination and channel estimation methods, which is characterized in that the step 1 specifically:
    The frequency domain of first OFDM training sequence symbols is sent into signal and is denoted as X1=[X1,0 X1,1 … X1,N-1]T, wherein Xi∈ { ± 1, ± j }, it is X that the frequency domain of second OFDM training sequence symbols, which sends signal,2=[X2,0 X2,1 … X2,N-1]T, then
    Wherein Φ is the diagonal matrix of N × N, X2I-th of element meetTwo The corresponding time-domain signal of symbol training sequence is respectively x1=FHX1, x2=FHX2, wherein FHIFFT unitary matrix is indicated, by each training The end L of symbolCPA symbol copies to before symbol and forms cyclic prefix, then is formed by time-domain training sequence and has and continuously follow Ring shift characteristics:
    Wherein
  3. 3. the joint narrowband in ofdm system according to claim 1 based on continuous cyclic shift training sequence interferes inspection Survey, elimination and channel estimation methods, which is characterized in that the step 2 specifically:
    2.1 calculate the decision statistics C of narrowband Interference Detection
    Assuming that channel is constant when keeping within two OFDM training sequence times, then time-domain training sequenceAfter channel Receiving signal y can indicate are as follows:
    WhereinIndicate convolution；H=[h0 h1 … hL-1]TIndicate the time domain impulse response of wireless multi-path channels, LCPBefore circulation Sew length,For 1 × (2N+2LCP+ L-1) time-domain received signal, take time domain to send Corresponding two segment length of signal [Seg2 Seg3 Seg1] is the reception signal of N
    Calculate the difference signal Δ y of two segment signals:
    Δ y=y2-y1
    Then decision statistics C are as follows:
    C=max (| FHΔy|) (3)
    WhereinExpression takes the maximum value of vector element；
    2.2 calculate decision threshold according to (4) formula:
    T=α × Med (| FHΔy|) (4)
    WhereinExpression takes the median of vector element,
    WhereinExpression rounds up,KmaxIndicate the maximum degree of rarefication of narrowband interference, INRminTable Show least interference noise ratio in need of consideration when system design, if C > T, there are narrowband interference for judgement；If C≤T judges No narrowband interference.
  4. 4. the joint narrowband in ofdm system according to claim 3 based on continuous cyclic shift training sequence interferes inspection Survey, elimination and channel estimation methods, which is characterized in that the step 5 specifically:
    It is equivalent at the integral multiple sub-carrier frequencies that the score overtones band offset and step 4 estimated using step 3 is estimated Signal reconstruction narrowband interferes time-domain signal, carries out time domain interference and eliminates, and obtains the training sequence after interference is eliminated and receives signal,
    5.1, R is interfered according to the time-domain narrowband that (11) and (12) formula reconstruct first OFDM symbol data part1With second OFDM The time-domain narrowband of symbol data part interferes R2:
    Wherein Table Show using independent variable vector element as the diagonal matrix of diagonal entry, FHIndicate IFFT unitary matrix；
    5.2, narrow-band interference excision is carried out to the training sequence time-domain signal received, obtains the reception signal after interference is eliminated
  5. 5. the joint narrowband in ofdm system according to claim 4 based on continuous cyclic shift training sequence interferes inspection Survey, elimination and channel estimation methods, which is characterized in that the step 6 specifically:
    Training sequence after being eliminated using interference is received signal or judges that the training sequence of no narrowband interference connects by step 2 detection The collection of letters number carries out a channel estimation；
    If 6.1, judging no narrowband interference by step 2, directly utilizeWithEstimate channel；If judgement exists Narrowband interference then utilizes the reception signal after narrow-band interference excisionWithEstimate channel；
    6.2, the channel frequency response on subcarrier is sought according to least square method, and takes mean value in two OFDM symbols；
    6.3, channel frequency response is subjected to inverse-Fourier transform to time domain, retains L before gained time-domain coefficientsCPA coefficient, By rear N-LCPA coefficient is set to zero, then by Fourier transform to frequency domain, obtains channel frequency response estimated value
    N is the number of sub carrier wave of ofdm system, X1Signal, X are sent for the frequency domain of first OFDM training sequence symbols2Second The frequency domain of OFDM training sequence symbols sends signal.
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