CN102811190A - 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 inhibition method that single-frequency is disturbed in a kind of OFDM (Orthogonal Frequency Division Multiplexing OFDM) communication system.
Background technology
OFDM is as a kind of modulation technique of multicarrier; The subcarrier of data through a plurality of mutually orthogonal low transmission rates transmitted, and the OFDM modulation and demodulation are handled and can be realized through employing Fast Fourier Transform Inverse (IFFT) and fast Fourier transform (FFT) respectively.Because each subcarrier is mutually orthogonal, the frequency spectrum after the modulation can be overlapped each other, has improved the availability of frequency spectrum greatly.In addition, because the phase mutual interference between the OFDM symbol of front and back has been isolated in the use of Cyclic Prefix (CP, Cyclic Prefix), make it have good anti-multipath interference performance; The bandwidth of each subcarrier is all very little, and the channel that is experienced can be similar to regards non-frequency-selective channel as, therefore greatly reduces the complexity of equilibrium treatment.On the other hand, compare with carrier wave communication system, also there are some shortcomings in ofdm communication system, as has higher peak-to-average force ratio, is subject to influence that carrier wave frequency deviation and single-frequency disturb etc.
In ofdm communication system, because the concentration of energy that single-frequency is disturbed on some or several number of sub-carrier, seriously influences even if the single-frequency of very little energy is disturbed also can cause the demodulation performance of OFDM.Disturb (can be called " interference of quadrature single-frequency ") when just in time overlapping when single-frequency, cause the sub-carrier signal-noise ratio of single-frequency interfering frequency position seriously to descend, but it is zero to the interference of adjacent sub-channel with some subcarriers; And when interfering frequency does not overlap (can be called " nonopiate single-frequency interference ") with subcarrier; Because the spectrum leakage that receiving terminal FFT window effect is brought; The frequency spectrum that non-orthogonal single-frequency is disturbed can be expanded within the frequency range of whole OFDM; In very big bandwidth range, have influence on a plurality of subcarriers, cause near near a plurality of subcarrier output signal-to-noise ratios the single-frequency interfering frequency seriously to descend.
In the prior art, the method for disturbing about the anti-single-frequency of ofdm communication system has a lot: adopt the method for chnnel coding to carry out frequency diversity; Adopt the multiple receive antenna technology to carry out space diversity; Adaptive disturbance is estimated, utilizes the single-frequency interference characteristic, obtains accurately duplicating of a single-frequency interference, in receiving signal, eliminates then; The receiving terminal windowing based on Cyclic Prefix and cyclic suffix, reduces energy leakage, suppresses single-frequency and disturbs the influence to useful signal; The anti-single-frequency interference of wavelet package transforms etc.The general weak point of these methods is the complexity and the robustness of its algorithm.Also having the most directly that method is the subcarrier shielding, but only on frequency domain, take the method for subcarrier shielding, is the passive interference that got around, and can not eliminate the influence of interference completely, particularly serious interference the time.
The notch filter that carries out corresponding frequency in time domain also is the method that the antagonism single-frequency used always is disturbed.Notch filter can be realized through FIR (limit for length's impulse response is arranged) or IIR (endless impulse response) mode.Compared to FIR, IIR is the recursion type filter, and adopting seldom, exponent number just can reach very sharp-pointed cut-off characteristics.Usually there is following several method to realize the IIR notch filter: through the All-pass Filter notch filter; Convert the notch filter of simulation into digital IIR notch filter; Lattice type IIR notch filter; Bilinearity second order IIR notch filter; Adopt zero limit algorithm design IIR notch filter.Adopt the IIR notch filter of zero limit algorithm design, have efficient, stable, accurately, rapid convergence, be easy to control, real-time, advantage such as robustness is good, but have the problem of symmetry and uncontrollable bandwidth gain simultaneously, further improvement.
The algorithm of digital Auto Gain control (DAGC) relates generally to power detection and thresholding compares, and its implementation mainly contains three kinds: feed forward type, reaction type, feedforward+reaction type.The convergence rate of feed forward type digital Auto Gain control ratio reaction type digital Auto Gain control wants fast; But when amplitude hit, there is distortion phenomenon; And reaction type automatic gain control circuit output waveform is level and smooth, but response speed is slower, and exists unsettled phenomenon (if automatic gain control loop is the level variation control by input signal; Then will cause unsettled impact and release time, and cause receiver performance to worsen).
Summary of the invention
The technical problem that the present invention will solve provides the inhibition method that single-frequency is disturbed in a kind of ofdm communication system, and when existing single-frequency to disturb in the ofdm communication system, the assurance system can normally move.
For solving the problems of the technologies described above; The inhibition method that single-frequency is disturbed in the ofdm communication system of the present invention is: adopt time domain and frequency domain to handle way of combining; Disturb for detected single-frequency, adopt IIR notch filter filtering single-frequency to disturb in time domain, and based on digital Auto Gain control adjustment signal power; When carrying out follow-up Digital Signal Processing with assurance, the signal input power is stabilized in optimum input power; At frequency domain the subcarrier that disturbed by single-frequency is carried out shielding processing.
In view of in the prior art, when ofdm communication system exists single-frequency to disturb, its performance will seriously descend, and the present invention proposes a kind of time domain and frequency domain and handle the interference of way of combining opposing single-frequency.Carry out notch filter in time domain and handle the interference of filtering single-frequency; Adopt digital Auto Gain control adjustment signal power to optimum input power; The amplitude of carrying out the mechanism adjusting data of gain-adjusted based on the average power signal drop is adopted in digital Auto Gain control; Avoid the definite problem of reference power, also be not subject to the influence of other factors; In the method that frequency domain takes subcarrier to shield, make to receive the subcarrier of single-frequency interference effect to be not used in transfer of data, thereby improved the performance that the anti-single-frequency of ofdm communication system is disturbed, and improved the throughput of system.
The present invention makes ofdm communication system can resist single-frequency very effectively and disturbs, and having solved when there is above-mentioned single-frequency interference in ofdm communication system can't operate as normal or the problem that worsens significantly of receptivity.
Description of drawings
Below in conjunction with accompanying drawing and embodiment the present invention is done further detailed explanation:
Fig. 1 is the ofdm communication system block diagram that has adopted the method for the invention to realize;
Fig. 2 is one embodiment frequency response of IIR notch filter and the zero pole distribution figure among Fig. 1;
Fig. 3 is the DAGC module one embodiment theory diagram among Fig. 1;
Fig. 4 is the sketch map that adopts finite states machine control and definite yield value.
Embodiment
The inhibition method that single-frequency is disturbed in the said ofdm communication system is to adopt time domain and frequency domain to handle way of combining opposing single-frequency to disturb, and concrete method is:
(1) at the ofdm communication system receiving terminal, on frequency domain, carry out the detection that single-frequency is disturbed, confirm frequency, strength information that single-frequency is disturbed.
(2), adopt the coefficient of improved zero limit algorithm computation second order IIR notch filter according to the frequency information of detected single-frequency interference.
(3) according to the coefficient that calculates, adopt the IIR notch filter to disturb the frequency at place to carry out notch filter in time domain and handle to single-frequency, the filtering single-frequency is disturbed.
(4) after receiving terminal carries out notch filter processing and low-pass filtering treatment, control is adjusted signal power based on digital Auto Gain, and when carrying out follow-up Digital Signal Processing with assurance, the signal input power is stabilized in optimum input power.
(5) transmitting terminal that the frequency of the detected single-frequency of receiving terminal being disturbed and strength information feed back to system, transmitting terminal shields the subcarrier of right quantity according to said frequency and strength information in the digital modulation processing, make it not secured transmission of payload data.Correspondingly, receiving terminal is skipped the subcarrier of corresponding conductively-closed in digital demodulation is handled.
The transmitting terminal of the ofdm communication system that method of the present invention realizes and the system block diagram of receiving terminal of being based on shown in Figure 1.The signal of communication handling process of this system is described below:
Transmitting terminal begins to transmit according to default configuration.The processing of transmitting terminal includes but not limited to; Binary data stream information via CRC (CRC) verification, scrambler, error correction coding, interleaving treatment (four is all optional); The single-frequency interfering frequency that when digital modulation, feeds back, interference strength information according to receiving terminal; And with the position relation of system effective subcarrier; Several possibly receive the subcarrier of single-frequency interference effect around suitably shielding interfering frequency place subcarrier; Carry out OFDM then and modulate (comprising processing such as inserting pilot tone, string and conversion, IFFT, also string conversion, insertion Cyclic Prefix), modulation data are afterwards carried out LPF, up-conversion, D/A (D/A) conversion, launch through radio frequency unit at last.
Receiving terminal carries out the detection that single-frequency is disturbed after starting reception, disturb if detect single-frequency, and then follow-up processing is handled according to the old process of ofdm communication system; If detected the single-frequency interference, then provide frequency and strength information that single-frequency is disturbed; IIR notch filter coefficients calculation block adopts the coefficient of improved zero limit algorithm computation second order IIR notch filter according to said frequency information; Based on said IIR notch filter coefficient, start the IIR notch filter and disturb with the filtering single-frequency.
The transmitting terminal that frequency that the detected single-frequency of receiving terminal is disturbed and strength information feed back to system.Can utilize backward channel to carry out the frequency of single-frequency interference and the feedback of strength information for intercommunication system,, then can utilize outband channel to carry out the frequency of single-frequency interference and the feedback of strength information for simplex system.
The transmitting terminal of system carries out corresponding subcarrier shielding based on the frequency and the strength information that disturb from the single-frequency that receiving terminal fed back.
Receiving terminal in system through the signal after the radio frequency processing, at first passes through A/D (mould/number) conversion process and radio frequency automatic gain control (AGC) adjustment and converts the digital signal that is in optimum input power into; Carry out notch filter through the IIR notch filter then, the filtering single-frequency is disturbed; Pass through Time and Frequency Synchronization, down-conversion, low-pass filtering treatment again; Signal after the processing is further adjusted signal power through digital Auto Gain control (DAGC); To guarantee that the signal input power that follow-up digital signal processing module is handled is stabilized in optimum input power, compensation is because the power fluctuation that notch filter and LPF caused; To through then and interference suppress and the adjusted signal that gains carries out OFDM demodulation (comprise Cyclic Prefix, string and conversion, FFT, and processing such as string conversion); Data after the demodulation are handled through balanced and digital demodulation; Carry out deinterleaving, error correction decoding, descrambling code, CRC check a series of conversion such as (four is all optional) at last, recover primary data information (pdi)., the digital demodulation of receiving terminal skips the subcarrier of said conductively-closed in handling, to avoid receiving single-frequency to disturb of the influence of the subcarrier of infringement to system's receptivity.
Below further disturb to handle and describe with regard to relevant anti-single-frequency such as IIR notch filter coefficient calculations, IIR notch filter, DAGC (digital Auto Gain control) and subcarrier shielding.The engineer that needed other processing should be this area in the system knows, and repeats no more here.
Chinese invention patent application " narrow band interference of explore frame detects the device and method that combines application with the BCH the decoding " (application number of submitting to referring to the applicant about the concrete processing method of single-frequency Interference Detection: 201110092176.0), here repeat no more.
1, design of IIR notch filter and coefficient calculations
IIR notch filter coefficients calculation block; According to detected single-frequency interfering frequency; Adopt improved zero limit algorithm to confirm coefficient, the frequency that disturb corresponding to single-frequency the zero point of its system function, its limit its bandwidth of rejection of decision and notch depth (are stablizing of assurance system; Limit must be in unit circle), and have symmetry and controlled passband gain.Corresponding trap frequency needs a second order IIR notch filter; The individual trap frequency of corresponding if desired n (n >=2) then can adopt the cascade of n second order IIR notch filter.
Be example with corresponding trap frequency below, the coefficient calculations method of said second order IIR notch filter is described.Corresponding trap frequency needs a second order IIR notch filter, and be z=e the zero point of this second order IIR notch filter
Jw, limit is p=re
Jw(r＜1) (0＜r＜1), following with the system function that zero limit algorithm obtains:
(1) formula is carried out abbreviation to be obtained system function and is:
Wherein, w is the trap centre frequency of this second order IIR notch filter, and r is the limit factor (0＜r＜1).If the single-frequency interfering frequency is f
i, the ofdm communication system sample frequency is f
s, the trap centre frequency w=2 π f of this second order IIR notch filter then
i/ f
s
Further, make it have symmetry and controlled passband gain through following improvement:
(1) gain that the notch filter coefficient is located at zero point and nyquist frequency (normalized radian frequency π) equates, through the differential seat angle of choose reasonable pole and zero, obtains the passband gain of symmetry.
(2) on the basis of symmetrical passband gain; Through changing the size of symmetrical passband gain notch filter amplitude function; The gain that makes this second order IIR notch filter locate at zero point and nyquist frequency (normalized radian frequency π) equates, and all equals k, separates the overdetermined equation about k; Utilize minimum quantization error to come estimated gain value k through the least square approximatioss, thereby obtain controlled passband gain.
System function form after the improvement is following:
Wherein, K is the passband gain value that sets, and A is this second order IIR notch filter gain adjustment constant, and φ is the angular deviation that this second order IIR notch filter improves the back pole and zero.
Through calculating abbreviation (the abbreviation process is obvious, belongs to common-sense to handle for the engineer of this area, repeats no more) here, the coefficient of the second order IIR notch filter that is designed is respectively:
a
1＝-(1+r
2)cos?w； a
2＝r
2；
b
1＝k(1+r
2)cos?w； (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 a positive integer, the representative data sequence number.
Fig. 2 (a) is the second order IIR notch filter that designed in the passband gain value is frequency response chart when getting different limit factor r values at 1 o'clock, and Fig. 2 (b) is corresponding zero pole distribution figure.Limit factor r value is represented the distance of limit from the center of circle, and this is apart from the resistance band and the notch depth that have determined second order IIR notch filter, and its span is 0＜r＜1.The r value is big more, and limit is big more from the distance in the center of circle, and the resistance band of second order IIR notch filter is narrow more, and notch depth is more little.Specifically choosing of passband gain value K and limit factor r value can be confirmed based on design experiences or emulation with reference to actual test result according to concrete requirement of system design, and realize with the form of configurable parameter.
2, IIR notch filter notch filter is handled
Difference equation based on formula (5) carries out the notch filter processing to the received data of receiving terminal, can the single-frequency interference filtering of corresponding frequencies be reduced single-frequency and disturb for the system communication Effect on Performance.Said IIR notch filter carries out notch filter to the digital signal after converting optimum input power into through radio frequency automatic gain control adjustment to be handled, and guarantees the influence that power is estimated and adjustment is not handled by notch filter all of radio frequency automatic gain control.
3, digital Auto Gain control (DAGC)
Said DAGC module is in order to compensate the average power signal drop that disturb in the adjacent band and the interior single-frequency of band disturbs process LPF (interference of filtering adjacent band) and notch filter (single-frequency is disturbed in the filtering band) processing to be brought; To carrying out the power adjustment through the signal after IIR notch filter and the low pass filter processing; The yield value that is about to its output and receiving terminal are handled and LPF multiplying each other of data afterwards through notch filter; The data amplitude is regulated, be stabilized in optimum input power to guarantee the signal input power that to carry out follow-up Digital Signal Processing.
The realization of DAGC is divided into three parts: the average power signal drop estimates, carry out the confirming of yield value, carry out gain-adjusted based on said yield value based on said average power signal drop estimated result.The DAGC module is got in the receiving terminal and is averaged the power estimation through the data after notch filter processing and the low-pass filtering treatment, and converts the power decibel value Pdagc of log-domain into; Pdagc and the estimated logarithm power decibel value Pagc of receiving terminal radio frequency automatic gain control (AGC) module are compared, obtain average power signal drop estimated value Pdiff (Pdiff=Pdagc-Pagc).Do not having the adjacent band to disturb or be not directed against the trap processing that single-frequency is disturbed in the big band, the power decibel value of the logarithm power decibel value that radio frequency AGC module is estimated in the system and the log-domain of DAGC module converts does not have obvious variation (the power fluctuation estimated value Pdiff that is log-domain is 0dB); Disturb in the adjacent band when existing, single-frequency is disturbed or during the notch filter processing in the band, and it (is Pdiff ≠ 0dB) that there are power fluctuation in Pdagc and Pagc.Based on said average power signal drop, carry out confirming and gain-adjusted of yield value among the present invention.The structure of DAGC and handling process are with reference to shown in Figure 3, and this scheme is controlled owing to being based on the power relative difference, so there is not definite problem of reference power, also is not subject to the influence of other factors.
The DAGC module continues to follow the tracks of, adjust in real time to signal power; Its yield value is controlled by finite state machine shown in Figure 4 and is confirmed.This finite state machine is divided into DAGC_IDLE (system reset), DAGC_ACQ (yield value coarse adjustment), DAGC_FADJ (yield value fine tuning) and 4 states of DAGC_LOCK (yield value locking), and each state and state transition condition are following:
(1) during system reset, finite state machine is got back to the DAGC_IDLE state.
(2) under the condition that system reset is removed and control enables to DAGC, move to the DAGC_ACQ state.
(3) at the 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 regulate to carrying out yield value with the direction of the opposite in sign of Pdiff with step-length gainStep4, even Pdiff＜0 then increases gainStep4 with yield value; If Pdiff＞0 then reduces gainStep4 with yield value; If the absolute value of average power drop estimated value Pdiff more than or equal to gain-adjusted thresholding DAGC_TH3 less than DAGC_TH4; Then regulate to carrying out yield value with step-length gainStep3 with the direction of the opposite in sign of Pdiff; Pdiff＜0 even; Then yield value is increased gainStep3, if Pdiff＞0 then reduces gainStep3 with yield value; If the absolute value of average power drop estimated value Pdiff more than or equal to gain-adjusted thresholding DAGC_TH2 less than DAGC_TH3; Then regulate to carrying out yield value with step-length gainStep2 with the direction of the opposite in sign of Pdiff; Pdiff＜0 even; Then yield value is increased gainStep2, if Pdiff＞0 then reduces gainStep2 with yield value; Do not regulate if the absolute value of average power drop estimated value Pdiff, does not then carry out any yield value less than gain-adjusted thresholding DAGC_TH2, keep original yield value constant.If yield value does not carry out the adjusting of step-length gainStep4 and gainStep3 in the DAGC_N1 frame in the past, and the adjusting number of times of step-length gainStep2 is then moved to the DAGC_LOCK state smaller or equal to DAGC_M1 time; If do not satisfy above-mentioned transition condition, then continue to remain on the DAGC_ACQ state and carry out above-mentioned yield value adjusting.
(4) under the DAGC_LOCK state, not carrying out yield value regulates; Average the power fluctuation estimation but follow the tracks of constantly; When the absolute value of the average power drop estimated value Pdiff that observes continuous DAGC_N2 frame more than or equal to gain-adjusted thresholding DAGC_TH5, then return the DAGC_ACQ state and remove to carry out yield value and regulate; If continuously the absolute value of the average power drop estimated value Pdiff of DAGC_N2 frame is less than DAGC_TH5 during more than or equal to gain-adjusted thresholding DAGC_TH6, then moves to the DAGC_FADJ state and carry out yield value and regulate; If do not satisfy above-mentioned two transition conditions, then continue to remain on the average power drop estimation tracking that the DAGC_LOCK state continues.Because influencing follow-up signal, gain-adjusted handles; Particularly all the more so such as QAM amplitude communication system for modulation such as (quadrature amplitude modulation) for adopting; Secondly the adjustment so at first should avoid gaining behind the entering lock-out state as far as possible should be avoided significantly regulating when needs are regulated as far as possible.
(5) at the DAGC_FADJ state; If the absolute value of average power drop estimated value Pdiff is during more than or equal to gain-adjusted thresholding DAGC_TH1; Then regulate to carrying out yield value with the direction of the opposite in sign of Pdiff with step-length gainStep1, even Pdiff＜0 then increases gainStep1 with yield value; If Pdiff＞0 then reduces gainStep1 with yield value; Do not regulate if the absolute value of average power drop estimated value Pdiff during less than gain-adjusted thresholding DAGC_TH1, does not then carry out any yield value, keep original yield value constant.If in the past in the DAGC_N1 frame yield value with the adjusting number of times of step-length gainStep1 smaller or equal to DAGC_M1 time, then move to the DAGC_LOCK state and proceed tracking; If do not satisfy above-mentioned transition condition, then continue to remain on the DAGC_FADJ state and carry out above-mentioned yield value adjusting.
Wherein, 0＜DAGC_TH1＜DAGC_TH2＜DAGC_TH3＜DAGC_TH4,0＜DAGC_TH6＜DAGC_TH5,0＜gainStep1＜gainStep2＜gainStep3＜gainStep4.The occurrence of each parameter can be confirmed based on design experiences or emulation with reference to actual test result according to concrete requirement of system design, and realize with the form of configurable parameter.
4, subcarrier in frequency domain shielding processing
Said subcarrier in frequency domain shielding processing; Be when system's transmitting terminal carries out the digital modulation processing; According to the outband channel of backward channel through intercommunication system or simplex system from single-frequency interfering frequency and strength information that receiving terminal fed back; Adequate shielding is the experimental process carrier wave of the certain limit at center with interfering frequency place subcarrier, makes it not secured transmission of payload data, and receiving terminal is then skipped the subcarrier in the corresponding shield ranges in receiving processing.Can further reduce single-frequency like this and disturb influence communication performance.The center subcarrier in the frequency information determinant carrier mask zone that single-frequency is disturbed, strength information has then determined the scope of this subcarrier shielding area, the scope of the bigger then subcarrier of intensity shielding area is then big more.
Below through to adopting 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 (towards the proposed projects of NGB cable access technology) " of the method that the anti-single-frequency of said ofdm communication system disturbs; 2010.) system embodiment carries out the emulation of anti-single-frequency jamming performance, verifies realizability of the present invention and validity.
In emulation, consider that single-frequency of the interior existence of effective bandwidth scope of HINOC system is disturbed, investigate the anti-single-frequency jamming performance of this system.From simulation result, when FER was the 1.00E-4 order of magnitude, HINOC system data frame adopted the QPSK modulation system, the performance improvement about 6dB of the performance when taking the present invention program when not taking this scheme; System adopts the 256QAM modulation system, the performance improvement about 3dB of the performance when taking the present invention program when not taking this programme.This shows that scheme provided by the invention can effectively improve the performance that the anti-single-frequency of HINOC system is disturbed.
Though be that example describes to exist single-frequency to disturb in the ofdm system among the above embodiment, the engineers and technicians of this area should be understood that method of the present invention can expand to the situation that exists a plurality of single-frequency to disturb in all ofdm communication systems naturally.For example; In a certain ofdm communication system, supposing the system exists M single-frequency to disturb, the information of then disturbing according to detected M single-frequency; The M point notch filter of forming by the cascade of M second order IIR notch filter according to the zero limit algorithm design that provides; Through the time domain trap, can eliminate this M single-frequency and disturb, and through DAGC adjustment power; The frequency, the strength information adequate shielding subcarrier that disturb according to each single-frequency simultaneously can reach anti-a plurality of single-frequency effects of jamming.
In sum, the method to the anti-single-frequency interference of ofdm communication system that the present invention disclosed is taked time domain and frequency domain way of combining, thereby has improved the performance that the anti-big single-frequency of ofdm system is disturbed.Certainly; The present invention also can have other various embodiments; Be applicable to the interference of anti-narrow band interference of other multicarrier modulation systems or single-frequency too; Under the situation that does not deviate from the present invention's spirit and its essence, those of ordinary skill in the art can make various corresponding changes and distortion according to the present invention, but these corresponding changes and distortion all should belong to the protection range of the appended claim of the present invention.
Claims (10)
1. the inhibition method that single-frequency is disturbed in the ofdm communication system; It is characterized in that: adopt time domain and frequency domain to handle way of combining; Disturb for detected single-frequency, adopt IIR notch filter filtering single-frequency to disturb in time domain, and based on digital Auto Gain control adjustment signal power; When carrying out follow-up Digital Signal Processing with assurance, the signal input power is stabilized in optimum input power; At frequency domain the subcarrier that disturbed by single-frequency is carried out shielding processing.
2. according to the described method of claim 1; It is characterized in that: adopt zero limit algorithm to confirm the coefficient of second order IIR notch filter; Determine by the single-frequency interfering frequency zero point of system function; The limit of system function is determined by desired bandwidth of rejection and notch depth, and has symmetry and controlled passband gain; The difference equation of said 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
2Be 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 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 a positive integer, the representative data sequence number.
3. according to the described method of claim 2, it is characterized in that: corresponding trap frequency, adopt a second order IIR notch filter; Corresponding n trap frequency then adopts the cascade of n second order IIR notch filter, wherein n >=2.
4. according to the described method of claim 1, it is characterized in that: said digital Auto Gain control comprises following three section processes: the average power signal drop is estimated, is carried out gain-adjusted based on said average power signal drop estimated result decision yield value with based on said yield value.
5. according to the described method of claim 4; It is characterized in that: said average power signal drop estimation approach is; Average power to the data after notch filter processing and LPF in the receiving terminal and estimate, and convert the decibel value Pdagc of log-domain into; Pdagc and the estimated logarithm power decibel value Pagc of receiving terminal radio frequency automatic gain control are compared, obtain average power signal drop estimated value Pdiff.
6. according to the described method of claim 4, it is characterized in that: said yield value is controlled by digital Auto Gain control finite state machine and is confirmed;
Said finite state machine is divided into system reset DAGC_IDLE, yield value coarse adjustment DAGC_ACQ, yield value fine tuning DAGC_FADJ and 4 states of yield value locking DAGC_LOCK, and the manner of execution of said finite state machine is described below:
When system reset, finite state machine is got back to the DAGC_IDLE state;
When system reset is removed and to digital Auto Gain when control enables, system by the DAGC_IDLE state transitions to the DAGC_ACQ state;
At the 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 regulate to carrying out yield value with the direction of the opposite in sign of Pdiff with step-length gainStep4, even Pdiff then reduces gainStep4 with yield value greater than 0; If Pdiff less than 0, then increases gainStep4 with yield value; If the absolute value of average power drop estimated value Pdiff more than or equal to gain-adjusted thresholding DAGC_TH3 less than DAGC_TH4; Then regulate to carrying out yield value with step-length gainStep3 with the direction of the opposite in sign of Pdiff; Even Pdiff is greater than 0; Then yield value is reduced gainStep3, if Pdiff less than 0, then increases gainStep3 with yield value; If the absolute value of average power drop estimated value Pdiff more than or equal to gain-adjusted thresholding DAGC_TH2 less than DAGC_TH3; Then regulate to carrying out yield value with step-length gainStep2 with the direction of the opposite in sign of Pdiff; Even Pdiff is greater than 0; Then yield value is reduced gainStep2, if Pdiff less than 0, then increases gainStep2 with yield value; If, then not carrying out any yield value less than gain-adjusted thresholding DAGC_TH2, do not regulate the absolute value of average power drop estimated value Pdiff; If yield value does not carry out the adjusting of step-length gainStep4 and gainStep3 in the DAGC_N1 frame in the past, and with the adjusting number of times of step-length gainStep2 smaller or equal to DAGC_M1 time, then move to the DAGC_LOCK state; If do not satisfy above-mentioned transition condition, then continue to remain on the DAGC_ACQ state and carry out above-mentioned yield value adjusting;
At the DAGC_LOCK state, average the Tracking Estimation of power fluctuation constantly, when the absolute value of the average power drop estimated value Pdiff that observes continuous DAGC_N2 frame more than or equal to DAGC_TH5, then return the DAGC_ACQ state and remove to carry out yield value and regulate; If continuously the absolute value of the average power drop estimated value Pdiff of DAGC_N2 frame is less than DAGC_TH5 during more than or equal to DAGC_TH6, then moves to the DAGC_FADJ state and carry out yield value and regulate; If do not satisfy above-mentioned two transition conditions, then continue to remain on the power fluctuation Tracking Estimation that the DAGC_LOCK state continues;
At the DAGC_FADJ state; When the absolute value of average power drop estimated value Pdiff during more than or equal to DAGC_TH1; Then regulate to carrying out yield value with the direction of the opposite in sign of Pdiff with step-length gainStep1, even Pdiff then reduces gainStep1 with yield value greater than 0; If Pdiff less than 0, then increases gainStep1 with yield value; If, then not carrying out any yield value less than DAGC_TH1, do not regulate the absolute value of average power drop estimated value Pdiff; If in the past in the DAGC_N1 frame yield value with the adjusting number of times of step-length gainStep1 smaller or equal to DAGC_M1 time, then move to the DAGC_LOCK state and proceed tracking; If do not satisfy above-mentioned transition condition, then continue to remain on the DAGC_FADJ state and carry out above-mentioned yield value adjusting;
Wherein, 0＜DAGC_TH1＜DAGC_TH2＜DAGC_TH3＜DAGC_TH4,0＜DAGC_TH6＜DAGC_TH5,0＜gainStep1＜gainStep2＜gainStep3＜gainStep4.
7. according to the described method of claim 4, it is characterized in that: said method of carrying out gain-adjusted is, with in said yield value and the receiving terminal through notch filter handle and LPF after data multiply each other, the data amplitude is regulated.
8. according to the described method of claim 1, it is characterized in that: said method of on frequency domain, the subcarrier that disturbed by single-frequency being carried out shielding processing is, the transmitting terminal that frequency that the detected single-frequency of the receiving terminal of system is disturbed and strength information feed back to system; The transmitting terminal of system based on the frequency and the strength information that disturb from the single-frequency that receiving terminal fed back, carries out corresponding subcarrier shielding in digital modulation is handled, make it not secured transmission of payload data; The receiving terminal of system is skipped the subcarrier in the corresponding subcarrier shield ranges in digital demodulation is handled.
9. according to the described method of claim 8; It is characterized in that: the method for the transmitting terminal that said frequency that the detected single-frequency of receiving terminal is disturbed and strength information feed back to system is; Utilize backward channel to carry out the frequency of single-frequency interference and the feedback of strength information for intercommunication system, then utilize outband channel to carry out the frequency of single-frequency interference and the feedback of strength information for simplex system.
10. according to claim 8 or 9 described methods; It is characterized in that: the center subcarrier in the frequency information determinant carrier mask zone that said single-frequency is disturbed; Said strength information has then determined the scope of this subcarrier shielding area, and the scope of the bigger then subcarrier of intensity shielding area is big more.
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