CN102811190B - Suppression method for single-frequency interference in OFDM (Orthogonal Frequency Division Multiplexing) communication system - Google Patents
Suppression method for single-frequency interference in OFDM (Orthogonal Frequency Division Multiplexing) communication system Download PDFInfo
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Abstract
The invention discloses a suppression method for single-frequency interference in an OFDM (Orthogonal Frequency Division Multiplexing) communication system. The suppression method comprises the following steps of: filtering the detected single-frequency interference in a time domain by an IIR (Infinite Impulse Response) notching filter through a time domain and frequency domain processing combination method, and regulating the signal power based on digital automatic gain control to ensure that the signal input powder is stabilized in the optimal input power when subsequent digital signal processes are carried out; and carrying out shielding processing on subcarriers interfered by single frequency in a frequency domain to ensure that effective data are not transmitted by the subcarriers. According to the method provided by the invention, the single-frequency interference can be effectively resisted, the single-frequency interference resistance of the OFDM communication system is improved, and the throughput of the system is improved; and when the single-frequency interference exits in the OFDM communication system, the normal operation of the system is guaranteed.
Description
Technical field
The present invention relates to digital communicating field, particularly relate to the suppressing method of mono-tone interference in a kind of OFDM (OrthogonalFrequency Division Multiplexing OFDM) communication system.
Background technology
OFDM is as a kind of modulation technique of multicarrier, transmitted by the subcarrier of data by multiple mutually orthogonal low transmission rate, OFDM modulation and demodulation process can realize respectively by employing Fast Fourier Transform Inverse (IFFT) and fast Fourier transform (FFT).Because each subcarrier is mutually orthogonal, the frequency spectrum after modulation can partly overlap mutually, substantially increases the availability of frequency spectrum.In addition, the mutual interference between the OFDM symbol of front and back has been isolated in the use due to Cyclic Prefix (CP, Cyclic Prefix), makes it have good anti-multipath jamming ability; The bandwidth of each subcarrier is very little, and the channel experienced can be similar to regards non-frequency-selective channel as, therefore greatly reduces the complexity of equilibrium treatment.On the other hand, compared with carrier wave communication system, also there are some shortcomings in ofdm communication system, as there is higher peak-to-average force ratio, being subject to the impact etc. of carrier wave frequency deviation and mono-tone interference.
In ofdm communication system, because the concentration of energy of mono-tone interference is on some or several subcarrier, even if the mono-tone interference of very little energy also can cause serious impact to the demodulation performance of OFDM.(can be called " orthogonal mono-tone interference ") when mono-tone interference just in time overlaps with some subcarriers, cause the sub-carrier signal-noise ratio degradation of mono-tone interference frequency location, but it is zero to the interference of adjacent sub-channel; And when interfering frequency does not overlap (can be called " nonopiate mono-tone interference ") with subcarrier, due to the spectrum leakage that receiving terminal FFT window effect brings, the frequency spectrum of non-orthogonal mono-tone interference can be extended within the frequency range of whole OFDM, in very large bandwidth range, have influence on multiple subcarrier, cause the multiple subcarrier output signal-to-noise ratio degradations near mono-tone interference frequency.
In prior art, the method about the anti-mono-tone interference of ofdm communication system has a lot: adopt the method for chnnel coding to carry out frequency diversity; Multiple receive antenna technology is adopted to carry out space diversity; Adaptive disturbance is estimated, utilizes mono-tone interference characteristic, obtains accurately copying of a mono-tone interference, then eliminate in Received signal strength; Receiving terminal windowing, based on Cyclic Prefix and cyclic suffix, reduces energy leakage, suppresses mono-tone interference on the impact of useful signal; The anti-mono-tone interference of wavelet package transforms etc.The general weak point of these methods is complexity and the robustness of its algorithm.Also have the most direct method to be subcarrier shielding, but on frequency domain, only take the method that subcarrier shield, be passive got around interference, the impact of interference can not be eliminated thoroughly, particularly when serious interference.
The notch filter carrying out corresponding frequency in time domain is also the method for conventional antagonism mono-tone interference.Notch filter can pass through FIR (having limit for length's impulse response) or IIR (endless impulse response) mode realizes.Be recursive filter device compared to FIR, IIR, adopt little exponent number just can reach very sharp-pointed cut-off characteristics.Usually following several method is had to realize IIR notch filter: by All-pass Filter notch filter; The notch filter of simulation is converted to digital IIR notch filter; Lattice IIR notch filter; Bilinearity second order IIR notch filter; Adopt zero pole point algorithm design IIR notch filter.Adopt the IIR notch filter of zero pole point algorithm design, have efficient, stable, accurately, rapid convergence, be easy to advantages such as controlling, real-time, robustness is good, but there is the problem of symmetry and uncontrollable bandwidth gain simultaneously, require further improvement.
The algorithm of digital resources obtainment (DAGC) relates generally to power detection and thresholding compares, and its implementation mainly contains three kinds: feed forward type, reaction type, feedforward+reaction type.Feed forward type digital resources obtainment is faster than the convergence rate of reaction type digital resources obtainment, but there is distortion phenomenon when amplitude hit, and reaction type automatic gain control circuit output waveform is level and smooth, but response speed is slower, and there is unstable phenomenon (if automatic gain control loop is changed by the level of input signal to control, then by causing unstable impact and release time, receiver performance is caused to worsen).
Summary of the invention
The technical problem to be solved in the present invention is to provide the suppressing method of mono-tone interference in a kind of ofdm communication system, and when there is mono-tone interference in ofdm communication system, guarantee system can normally be run.
For solving the problems of the technologies described above, in ofdm communication system of the present invention, the suppressing method of mono-tone interference is: adopt the way that time domain and frequency domain process combine, for detected mono-tone interference, IIR notch filter filtering mono-tone interference is adopted in time domain, and based on digital resources obtainment adjustment signal power, during to ensure to carry out subsequent digital signal process, signal input power is stabilized in optimum input power; At frequency domain, shielding processing is carried out to the subcarrier by mono-tone interference;
Adopt the coefficient of zero pole point algorithm determination second order IIR notch filter, the zero point of system function is determined by mono-tone interference frequency, and the limit of system function is determined by required bandwidth of rejection and notch depth, and has symmetrical and controlled passband gain; The difference equation of described second order IIR notch filter is shown below:
y(n)＝b
0x(n)+b
1x(n-1)+b
2x(n-2)-a
1y(n-1)-a
2y(n-2)；
Wherein, a
1, a
2, b
0, b
1, b
2for the coefficient of second order IIR notch filter, a
1=-(1+r
2) cosw; a
2=r
2;
b
1=k (1+r
2) cosw; W is the trap centre frequency of this second order IIR notch filter, and k is the passband gain value of this second order IIR notch filter, and r is the limit factor, represents the distance of limit from the center of circle, 0<r<1; X (n) is the list entries of second order IIR notch filter, and y (n) is the output sequence of second order IIR notch filter; N is positive integer, representative data sequence number.
In view of in prior art, when ofdm communication system exists mono-tone interference, its performance, by degradation, the present invention proposes the way opposing mono-tone interference that a kind of time domain and frequency domain process combine.Notch filter process filtering mono-tone interference is carried out in time domain, adopt digital resources obtainment adjustment signal power to optimum input power, digital resources obtainment adopts the amplitude of the mechanism adjustment data of carrying out gain-adjusted based on average power signal drop, avoid the problem that reference power is determined, be not also subject to the impact of other factors; In the method that frequency domain takes subcarrier to shield, make the subcarrier affected by mono-tone interference be not used in transfer of data, thus improve the performance of the anti-mono-tone interference of ofdm communication system, and improve the throughput of system.
The present invention enables ofdm communication system effectively resist mono-tone interference, solves and cannot normally to work when ofdm communication system exists above-mentioned mono-tone interference or problem that receptivity significantly worsens.
Accompanying drawing explanation
Below in conjunction with accompanying drawing and embodiment, the present invention is further detailed explanation:
Fig. 1 is the ofdm communication system block diagram that have employed the method for the invention realization;
Fig. 2 is IIR notch filter one embodiment frequency response in Fig. 1 and zero-pole map;
Fig. 3 is the DAGC module one embodiment theory diagram in Fig. 1;
Fig. 4 is the schematic diagram adopting finite states machine control and determine yield value.
Embodiment
In described ofdm communication system, the suppressing method of mono-tone interference is the way opposing mono-tone interference adopting time domain and frequency domain process to combine, and concrete method is:
(1) at ofdm communication system receiving terminal, frequency domain carries out the detection of mono-tone interference, determine the frequency of mono-tone interference, strength information.
(2) according to the frequency information of the mono-tone interference detected, the zero pole point algorithm improved is adopted to calculate the coefficient of second order IIR notch filter.
(3) according to the coefficient calculated, IIR notch filter is adopted to carry out notch filter process for the frequency at mono-tone interference place, filtering mono-tone interference in time domain.
(4) after receiving terminal carries out notch filter process and low-pass filtering treatment, adjust signal power based on digital resources obtainment, during to ensure to carry out subsequent digital signal process, signal input power is stabilized in optimum input power.
(5) frequency of the mono-tone interference detected by receiving terminal and strength information are fed back to the transmitting terminal of system, transmitting terminal shields the subcarrier of right quantity according to described frequency and strength information in digital modulation process, makes it not secured transmission of payload data.Correspondingly, receiving terminal skips the subcarrier of corresponding conductively-closed in digital demodulation process.
The transmitting terminal of ofdm communication system and the system block diagram of receiving terminal that realize based on method of the present invention shown in Fig. 1.The signal of communication handling process of this system is as described below:
Transmitting terminal starts to transmit according to default configuration.The process of transmitting terminal includes but not limited to, binary data stream information verifies through CRC (cyclic redundancy check (CRC) code), scrambler, error correction coding, interleaving treatment (four is all optional), when digital modulation according to the mono-tone interference frequency that receiving terminal feeds back, interference strength information, and with the position relationship of the effective subcarrier of system, suitably around the subcarrier of shielding interfering frequency place, several may be subject to the subcarrier of mono-tone interference impact, then carry out OFDM modulation and (comprise insertion pilot tone, serioparallel exchange, IFFT, parallel-serial conversion, insert the process such as Cyclic Prefix), data after modulation carry out low-pass filtering, up-conversion, D/A (D/A) changes, eventually pass radio frequency unit to launch.
Receiving terminal carries out the detection of mono-tone interference after starting reception, if mono-tone interference do not detected, then follow-up process is according to the old process process of ofdm communication system; If detect mono-tone interference, then provide frequency and the strength information of mono-tone interference; IIR notch filter coefficients calculation block adopts the zero pole point algorithm improved to calculate the coefficient of second order IIR notch filter according to described frequency information; Based on described IIR notch filter coefficient, start IIR notch filter with filtering mono-tone interference.
The frequency of the mono-tone interference detected by receiving terminal and strength information are fed back to the transmitting terminal of system.Backward channel can be utilized to carry out the frequency of mono-tone interference and the feedback of strength information for intercommunication system, for simplex system, then outband channel can be utilized to carry out the frequency of mono-tone interference and the feedback of strength information.
The transmitting terminal of system, based on the frequency of the mono-tone interference fed back from receiving terminal and strength information, carries out corresponding subcarrier shielding.
At the receiving terminal of system, the signal after radio frequency processing, is first converted to through A/D (mould/number) conversion process and radio frequency automatic growth control (AGC) adjustment the digital signal being in optimum input power; Then notch filter is carried out through IIR notch filter, filtering mono-tone interference; Again through Time and Frequency Synchronization, down-conversion, low-pass filtering treatment; Signal after process adjusts signal power further through digital resources obtainment (DAGC), to ensure that the signal input power of subsequent digital signal processing module process is stabilized in optimum input power, compensate the power fluctuation because notch filter and low-pass filtering cause; Then the signal after AF panel and Gain tuning is carried out OFDM demodulation (comprising the process such as Cyclic Prefix, serioparallel exchange, FFT, parallel-serial conversion), data after demodulation are through balanced and digital demodulation process, finally carry out a series of conversion such as deinterleaving, error correction decoding, descrambling code, CRC check (four is all optional), recover primary data information (pdi).The subcarrier of described conductively-closed is skipped, to avoid the impact of the subcarrier pair system acceptance performance by mono-tone interference infringement in the digital demodulation process of receiving terminal.
Below be described with regard to the relevant anti-mono-tone interference process such as IIR notch filter coefficient calculations, IIR notch filter, DAGC (digital resources obtainment) and subcarrier shielding further.The engineer that other process required in system should be this area knows, and repeats no more herein.
(application number: 201110092176.0), repeats no more the Chinese invention patent application device and method of connected applications " the arrowband Interference Detection of explore frame and the BCH decode " submitted to see the applicant of the concrete processing method detected about mono-tone interference herein.
1, the design of IIR notch filter and coefficient calculations
IIR notch filter coefficients calculation block, according to the mono-tone interference frequency detected, adopt the zero pole point algorithm determination coefficient improved, correspond to the frequency of mono-tone interference the zero point of its system function, its limit determines that its bandwidth of rejection and notch depth (are stablizing of guarantee system, limit must in unit circle), and there is symmetrical and controlled passband gain.A corresponding trap frequency, needs a second order IIR notch filter; If need corresponding n (n≤2) individual trap frequency, then can adopt the cascade of n second order IIR notch filter.
Below for a corresponding trap frequency, the coefficient calculation method of described second order IIR notch filter is described.A corresponding trap frequency, need a second order IIR notch filter, the zero point of this second order IIR notch filter is z=e
jw, limit is p=re
jw(r < 1) (0<r<1), the system function obtained with zero pole point algorithm is as follows:
(1) formula is carried out abbreviation to obtain system function and be:
Wherein, w is the trap centre frequency of this second order IIR notch filter, and r is the limit factor (0<r<1).If mono-tone interference frequency is f
i, ofdm communication system sample frequency is f
s, then the trap centre frequency w=2 π f of this second order IIR notch filter
i/ f
s.
Further by following improvement, make it have symmetrical and controlled passband gain:
(1) make notch filter coefficient equal in the gain at zero point and nyquist frequency (normalized radian frequency π) place, by the differential seat angle of choose reasonable pole and zero, obtain symmetrical passband gain.
(2) on the basis of symmetrical passband gain, by changing the size of symmetrical passband gain notch filter amplitude function, make this second order IIR notch filter equal in the gain at zero point and nyquist frequency (normalized radian frequency π) place, and all equal k, solution is about the overdetermined equation of k, utilize minimum quantization error to carry out estimated gain value k by Least squares approximation method, thus obtain controlled passband gain.
System function form after improvement is as follows:
Wherein, K is set passband gain value, and A is this second order IIR notch filter Gain tuning constant, and φ is the angular deviation of pole and zero after this second order IIR notch filter improves.
By calculating abbreviation (abbreviation process is apparent, and the engineer for this area belongs to common-sense process, repeats no more) here, the coefficient of designed second order IIR notch filter is respectively:
a
1＝-(1+r
2)cosw；a
2＝r
2；
b
1＝k(1+r
2)cosw； (4)
The difference equation of corresponding second order IIR notch filter is:
y(n)＝b
0x(n)+b
1x(n-1)+b
2x(n-2)-a
1y(n-1)-a
2y(n-2) (5)。
Wherein, x (n) is the list entries of second order IIR notch filter, and y (n) is the output sequence of second order IIR notch filter; N is positive integer, representative data sequence number.
Fig. 2 (a) for frequency response chart different limit factor r values got by designed second order IIR notch filter during when passband gain value is 1, Fig. 2 (b) be corresponding zero-pole map.Limit factor r value represents the distance of limit from the center of circle, and this distance determines resistance band and the notch depth of second order IIR notch filter, and its span is 0<r<1.R value is larger, and limit is larger from the distance in the center of circle, and the resistance band of second order IIR notch filter is narrower, and notch depth is less.Specifically choosing of passband gain value K and limit factor r value according to concrete requirement of system design based on design experiences or emulation with determine with reference to actual test result, and can realize with the form of configurable parameter.
2, IIR notch filter notch filter process
Difference equation based on formula (5) carries out notch filter process to the data received by receiving terminal, by the mono-tone interference filtering of corresponding frequencies, can reduce the impact of mono-tone interference for system communication performance.Described IIR notch filter carries out notch filter process to the digital signal after being converted to optimum input power through the adjustment of radio frequency automatic growth control, and the power Estimation and rectification guaranteeing radio frequency automatic growth control is not all by the impact of notch filter process.
3, digital resources obtainment (DAGC)
Described DAGC module processes through low-pass filtering (interference of filtering adjacent band) and notch filter (in filter out-band mono-tone interference) the average power signal drop brought in order to compensate mono-tone interference in adjacent band interference and band, power adjustment is carried out to the signal after IIR notch filter and low pass filter process, by its yield value and receiving terminal exported being multiplied of data after notch filter process with low-pass filtering, data amplitude is regulated, to ensure that the signal input power need carrying out subsequent digital signal process is stabilized in optimum input power.
The realization of DAGC is divided into three parts: average power signal drop estimate, carry out based on described average power signal drop estimated result yield value determination, carry out gain-adjusted based on described yield value.The DAGC module data of getting in receiving terminal after notch filter process and the low-pass filtering treatment power that is averaged is estimated, and is converted to the power decibels value Pdagc of log-domain; Log power decibel value Pagc estimated by Pdagc and receiving terminal radio frequency automatic growth control (AGC) module is compared, obtains average power signal drop estimated value Pdiff (Pdiff=Pdagc-Pagc).In the trap process not having adjacent band to disturb or do not carry out for mono-tone interference in large band, the power decibels value of the log power decibel value that in system, radio frequency AGC module is estimated and the log-domain of DAGC module converts does not significantly change (namely the power fluctuation estimated value Pdiff of log-domain is 0dB); When there is mono-tone interference or notch filter process in adjacent band interference, band, there is power fluctuation (i.e. Pdiff ≠ 0dB) in Pdagc and Pagc.Based on described average power signal drop in the present invention, carry out determination and the gain-adjusted of yield value.The structure of DAGC and handling process are with reference to shown in Fig. 3, and this scheme, owing to being control based on power relative difference, so there is not the problem identificatioin of reference power, is not subject to the impact of other factors yet.
DAGC module carries out continuing to follow the tracks of, adjust in real time to signal power; Its yield value finite state machine as shown in Figure 4 carries out controlling and determining.This finite state machine is divided into DAGC_IDLE (system reset), DAGC_ACQ (yield value coarse adjustment), DAGC_FADJ (yield value fine tuning) and DAGC_LOCK (yield value locking) 4 states, each state and state transition condition as follows:
(1), during system reset, finite state machine gets back to DAGC_IDLE state.
(2) remove when system reset and under enable condition is controlled to DAGC, move to DAGC_ACQ state.
(3) in DAGC_ACQ state, if the absolute value of average power drop estimated value Pdiff is more than or equal to gain-adjusted thresholding DAGC_TH4, then carry out yield value adjustment to the direction contrary with the symbol of Pdiff with step-length gainStep4, even Pdiff<0, then yield value is increased gainStep4, if Pdiff>0, then yield value is reduced gainStep4; If the absolute value of average power drop estimated value Pdiff is more than or equal to gain-adjusted thresholding DAGC_TH3 and is less than DAGC_TH4, then carry out yield value adjustment to the direction contrary with the symbol of Pdiff with step-length gainStep3, even Pdiff<0, then yield value is increased gainStep3, if Pdiff>0, then yield value is reduced gainStep3; If the absolute value of average power drop estimated value Pdiff is more than or equal to gain-adjusted thresholding DAGC_TH2 and is less than DAGC_TH3, then carry out yield value adjustment to the direction contrary with the symbol of Pdiff with step-length gainStep2, even Pdiff<0, then yield value is increased gainStep2, if Pdiff>0, then yield value is reduced gainStep2; If the absolute value of average power drop estimated value Pdiff is less than gain-adjusted thresholding DAGC_TH2, then do not carry out any yield value adjustment, keep original yield value constant.If in DAGC_N1 frame, yield value does not carry out the adjustment of step-length gainStep4 and gainStep3 in the past, and the adjustment number of times of step-length gainStep2 is less than or equal to DAGC_M1 time, then move to DAGC_LOCK state; If do not meet above-mentioned transition condition, then continue to remain on DAGC_ACQ state and carry out above-mentioned yield value adjustment.
(4) under DAGC_LOCK state, yield value adjustment is not carried out, but follow the tracks of the power fluctuation that is averaged constantly to estimate, when the absolute value of the average power drop estimated value Pdiff observing continuous DAGC_N2 frame is more than or equal to gain-adjusted thresholding DAGC_TH5, then return DAGC_ACQ state and go to carry out yield value adjustment; If when the absolute value of the average power drop estimated value Pdiff of DAGC_N2 frame is less than DAGC_TH5 and is more than or equal to gain-adjusted thresholding DAGC_TH6 continuously, then move to DAGC_FADJ state and carry out yield value adjustment; If the absolute value not meeting the average power drop estimated value Pdiff of continuous DAGC_N2 frame is more than or equal to DAGC_TH5, or the absolute value of the continuous average power drop estimated value Pdiff of DAGC_N2 frame is less than DAGC_TH5 and is more than or equal to DAGC_TH6, then continue to remain on the average power drop that DAGC_LOCK state carries out continuing and estimate to follow the tracks of.Because gain-adjusted affects follow-up signal process, particularly all the more so for adopting the communication system of the amplitude modulation(PAM)s such as such as QAM (quadrature amplitude modulation), so first should avoid after entering lock-out state carrying out Gain tuning as far as possible, secondly should avoid when needs regulate significantly regulating as far as possible.
(5) in DAGC_FADJ state, if when the absolute value of average power drop estimated value Pdiff is more than or equal to gain-adjusted thresholding DAGC_TH1, then carry out yield value adjustment to the direction contrary with the symbol of Pdiff with step-length gainStep1, even Pdiff<0, then yield value is increased gainStep1, if Pdiff>0, then yield value is reduced gainStep1; If when the absolute value of average power drop estimated value Pdiff is less than gain-adjusted thresholding DAGC_TH1, then do not carry out any yield value adjustment, keep original yield value constant.If yield value is less than or equal to DAGC_M1 time with the adjustment number of times of step-length gainStep1 in DAGC_N1 frame in the past, then moves to DAGC_LOCK state and proceed to follow the tracks of; If yield value is less than or equal to DAGC_M1 time with the adjustment number of times of step-length gainStep1 in satisfied DAGC_N1 frame in the past, then continues to remain on DAGC_FADJ state and carry out above-mentioned yield value adjustment.
Wherein, 0<DAGC_TH1<DAGC_TH2LEssT.LTssT .LTDAGC_TH3<DAGC_TH4,0<DAGC_TH6<DAGC_TH5,0<gainStep1<gainStep2LEssT.LTs sT.LTgainStep3<gainStep4.The occurrence of each parameter according to concrete requirement of system design based on design experiences or emulation with determine with reference to actual test result, and can realize with the form of configurable parameter.
4, subcarrier in frequency domain shielding processing
Described subcarrier in frequency domain shielding processing, when system transmitting terminal carries out digital modulation process, according to the mono-tone interference frequency fed back from receiving terminal by the backward channel of intercommunication system or the outband channel of simplex system and strength information, several subcarriers of the certain limit of adequate shielding centered by the subcarrier of interfering frequency place, make it not secured transmission of payload data, receiving terminal then skips the subcarrier in corresponding shield ranges in reception process.The impact of mono-tone interference on communication performance can be reduced further like this.The central subcarrier in the frequency information determinant carrier mask region of mono-tone interference, strength information then determines the scope of this subcarrier shielding area, and the scope of intensity larger then subcarrier shielding area is then larger.
Below by the HINOC (the State Administration of Radio, Film and Television Broadcasting Institute of Science and Technology etc.: " high-performance coaxial cable access network (HINOC) physical layer transmission pattern and Medium Access Control Protocol (proposed projects towards NGB cable access technology) " of the method to the anti-mono-tone interference of the described ofdm communication system of employing, 2010.) system embodiment carries out anti-mono-tone interference performance simulation, verifies realizability of the present invention and validity.
In simulations, there is a mono-tone interference within the scope of the effective bandwidth of consideration HINOC system, investigate the anti-mono-tone interference performance of this system.From simulation result, when frame error rate is the 1.00E-4 order of magnitude, HINOC system data frame adopts QPSK modulation system, takes Performance Ratio during the present invention program not take the performance improvement during program to be about 6dB; System adopts 256QAM modulation system, takes Performance Ratio during the present invention program not take performance improvement during this programme to be about 3dB.As can be seen here, scheme provided by the invention effectively can improve the performance of the anti-mono-tone interference of HINOC system.
Although be described there is a mono-tone interference in ofdm system in above embodiment, the engineers and technicians of this area should be understood that method of the present invention can expand to the situation that there is multiple mono-tone interference in all ofdm communication systems naturally.Such as, in a certain ofdm communication system, there is M mono-tone interference in supposing the system, then according to the information of M the mono-tone interference detected, the M point notch filter be made up of the cascade of M second order IIR notch filter according to the zero pole point algorithm design provided, through time domain trap, this M mono-tone interference can be eliminated, and by DAGC Modulating Power; Simultaneously according to frequency, the strength information adequate shielding subcarrier of each mono-tone interference, the effect of anti-multiple mono-tone interference can be reached.
In sum, the method for the anti-mono-tone interference of ofdm communication system disclosed by the present invention, takes the way that time domain and frequency domain combine, thus improves the performance that ofdm system resists larger mono-tone interference.
Certainly; the present invention also can have other various embodiments; be applicable to the anti-arrowband interference of other multicarrier modulation systems or mono-tone interference too; when not deviating from the present invention's spirit and its essence; those of ordinary skill in the art can make various corresponding change and distortion according to the present invention, but these change accordingly and are out of shape the protection range that all should belong to the claim appended by the present invention.
Claims (9)
1. the suppressing method of mono-tone interference in an ofdm communication system, it is characterized in that: adopt the way that time domain and frequency domain process combine, for detected mono-tone interference, IIR notch filter filtering mono-tone interference is adopted in time domain, and based on digital resources obtainment adjustment signal power, during to ensure to carry out subsequent digital signal process, signal input power is stabilized in optimum input power; At frequency domain, shielding processing is carried out to the subcarrier by mono-tone interference;
Adopt the coefficient of zero pole point algorithm determination second order IIR notch filter, the zero point of system function is determined by mono-tone interference frequency, and the limit of system function is determined by required bandwidth of rejection and notch depth, and has symmetrical and controlled passband gain; The difference equation of described second order IIR notch filter is shown below:
y(n)＝b
0x(n)+b
1x(n-1)+b
2x(n-2)-a
1y(n-1)-a
2y(n-2)；
Wherein, a
1, a
2, b
0, b
1, b
2for the coefficient of second order IIR notch filter, a
1=-(1+r
2) cosw; a
2=r
2;
b
1=k (1+r
2) cosw; W is the trap centre frequency of this second order IIR notch filter, and k is the passband gain value of this second order IIR notch filter, and r is the limit factor, represents the distance of limit from the center of circle, 0<r<1; X (n) is the list entries of second order IIR notch filter, and y (n) is the output sequence of second order IIR notch filter; N is positive integer, representative data sequence number.
2. in accordance with the method for claim 1, it is characterized in that: a corresponding trap frequency, adopts a second order IIR notch filter; Corresponding n trap frequency, then adopt the cascade of n second order IIR notch filter, wherein n≤2.
3. in accordance with the method for claim 1, it is characterized in that: described digital resources obtainment comprises following three part process: average power signal drop is estimated, determine yield value based on described average power signal drop estimated result and carry out gain-adjusted based on described yield value.
4. in accordance with the method for claim 3, it is characterized in that: the method that described average power signal drop is estimated is, estimate for the power that is averaged of the data in receiving terminal after notch filter process and low-pass filtering, and be converted to the decibel value Pdagc of log-domain; Log power decibel value Pagc estimated by Pdagc and receiving terminal radio frequency automatic growth control is compared, obtains average power signal drop estimated value Pdiff.
5. in accordance with the method for claim 3, it is characterized in that: described yield value is controlled by digital resources obtainment finite state machine and determines;
Described finite state machine is divided into system reset DAGC_IDLE, yield value coarse adjustment DAGC_ACQ, yield value fine tuning DAGC_FADJ and yield value locking DAGC_LOCK 4 states, and the manner of execution of described finite state machine is as described below:
Upon system reset, finite state machine gets back to DAGC_IDLE state;
When system reset remove and enable to digital resources obtainment time, system by DAGC_IDLE state transitions to DAGC_ACQ state;
In DAGC_ACQ state, if the absolute value of average power drop estimated value Pdiff is more than or equal to gain-adjusted thresholding DAGC_TH4, then carry out yield value adjustment to the direction contrary with the symbol of Pdiff with step-length gainStep4, even Pdiff is greater than 0, then yield value is reduced gainStep4, if Pdiff is less than 0, then yield value is increased gainStep4; If the absolute value of average power drop estimated value Pdiff is more than or equal to gain-adjusted thresholding DAGC_TH3 and is less than DAGC_TH4, then carry out yield value adjustment to the direction contrary with the symbol of Pdiff with step-length gainStep3, even Pdiff is greater than 0, then yield value is reduced gainStep3, if Pdiff is less than 0, then yield value is increased gainStep3; If the absolute value of average power drop estimated value Pdiff is more than or equal to gain-adjusted thresholding DAGC_TH2 and is less than DAGC_TH3, then carry out yield value adjustment to the direction contrary with the symbol of Pdiff with step-length gainStep2, even Pdiff is greater than 0, then yield value is reduced gainStep2, if Pdiff is less than 0, then yield value is increased gainStep2; If the absolute value of average power drop estimated value Pdiff is less than gain-adjusted thresholding DAGC_TH2, then do not carry out any yield value adjustment; If yield value does not carry out the adjustment of step-length gainStep4 and gainStep3 in DAGC_N1 frame in the past, and be less than or equal to DAGC_M1 time with the adjustment number of times of step-length gainStep2, then move to DAGC_LOCK state; If do not meet above-mentioned transition condition, then continue to remain on DAGC_ACQ state and carry out above-mentioned yield value adjustment;
In DAGC_LOCK state, the tracking of the power fluctuation that is averaged constantly is estimated, when the absolute value of the average power drop estimated value Pdiff observing continuous DAGC_N2 frame is more than or equal to DAGC_TH5, then returns DAGC_ACQ state and goes to carry out yield value adjustment; If when the absolute value of the average power drop estimated value Pdiff of DAGC_N2 frame is less than DAGC_TH5 and is more than or equal to DAGC_TH6 continuously, then move to DAGC_FADJ state and carry out yield value adjustment; If the absolute value not meeting the average power drop estimated value Pdiff of continuous DAGC_N2 frame is more than or equal to DAGC_TH5, or the absolute value of the continuous average power drop estimated value Pdiff of DAGC_N2 frame is less than DAGC_TH5 and is more than or equal to DAGC_TH6, then continue to remain on power fluctuation that DAGC_LOCK state carries out continuing and follow the tracks of and estimate;
In DAGC_FADJ state, when the absolute value of average power drop estimated value Pdiff is more than or equal to DAGC_TH1, then carry out yield value adjustment to the direction contrary with the symbol of Pdiff with step-length gainStep1, even Pdiff is greater than 0, then yield value is reduced gainStep1, if Pdiff is less than 0, then yield value is increased gainStep1; If the absolute value of average power drop estimated value Pdiff is less than DAGC_TH1, then do not carry out any yield value adjustment; If yield value is less than or equal to DAGC_M1 time with the adjustment number of times of step-length gainStep1 in DAGC_N1 frame in the past, then moves to DAGC_LOCK state and proceed to follow the tracks of; If yield value is less than or equal to DAGC_M1 time with the adjustment number of times of step-length gainStep1 in satisfied DAGC_N1 frame in the past, then continues to remain on DAGC_FADJ state and carry out above-mentioned yield value adjustment;
Wherein, 0<DAGC_TH1<DAGC_TH2LEssT.LTssT .LTDAGC_TH3<DAGC_TH4,0<DAGC_TH6<DAGC_TH5,0<gainStep1<gainStep2LEssT.LTs sT.LTgainStep3<gainStep4.
6. in accordance with the method for claim 3, it is characterized in that: described in carry out gain-adjusted method be described yield value is multiplied with the data in receiving terminal after notch filter process with low-pass filtering, data amplitude is regulated.
7. in accordance with the method for claim 1, it is characterized in that: described method of carrying out shielding processing to the subcarrier by mono-tone interference on frequency domain the frequency of the mono-tone interference detected by the receiving terminal of system and strength information is fed back to the transmitting terminal of system; The transmitting terminal of system based on the frequency of the mono-tone interference fed back from receiving terminal and strength information, carries out corresponding subcarrier shielding, makes it not secured transmission of payload data in digital modulation process; The receiving terminal of system skips the subcarrier in corresponding subcarrier shield ranges in digital demodulation process.
8. in accordance with the method for claim 7, it is characterized in that: the described method frequency of the mono-tone interference detected by receiving terminal and strength information being fed back to the transmitting terminal of system is, utilize backward channel to carry out the frequency of mono-tone interference and the feedback of strength information for intercommunication system, then utilize outband channel to carry out the frequency of mono-tone interference and the feedback of strength information for simplex system.
9. according to the method described in claim 7 or 8, it is characterized in that: the central subcarrier in the frequency information determinant carrier mask region of described mono-tone interference, described strength information then determines the scope of this subcarrier shielding area, and the scope of intensity larger then subcarrier shielding area is larger.
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