CN100555904C - Digital multi-media broadcast direct broadcast station multipath echo removing method - Google Patents
Digital multi-media broadcast direct broadcast station multipath echo removing method Download PDFInfo
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Abstract
A kind of digital multi-media broadcast direct broadcast station multipath echo removing method belongs to wireless communication technology field.The present invention utilizes a self adaptation finite length filtering device to come analog digital multi-media broadcast direct broadcast station transmitting antenna to the coupling of the multipath between reception antenna channel, the tap coefficient of this self adaptation finite length filtering device utilize above-mentioned repeater to transmit by one and received signal between the least mean-square error adaptive algorithm of uncorrelated characteristic upgrade, after this self adaptation finite length filtering device filtering of transmitted reference signal process that directly coupling is come of transmitting antenna end, simulate actual echo-signal, from received signal, deduct the interference that this analog echo signal can effectively be eliminated multipath echo.The present invention has simplified computation complexity, thereby can be adapted to the transmitting-receiving multipath coupling environment within 10 microseconds well, and the processing time that whole multipath echo is eliminated thereby can not influence the performance of whole network within 20 microseconds.
Description
Technical field
The present invention relates to a kind of method for echo cancellation of wireless communication technology field, specifically is a kind of digital multi-media broadcast direct broadcast station multipath echo removing method.
Background technology
How to guarantee that for the digital multimedia terrestrial broadcast system its maximum coverage exists certain technical difficulty.The line-of-sight propagation characteristic of broadcasting has determined that this broadcasting system needs a large amount of transmitter and many complicated distributed signal transmitting systems now.In traditional out of use occasion of covering expansion scheme, the repeater is one and more reasonably selects.The function of repeater is exactly to forward after directly the co-channel signal that receives being amplified, and adopts directional antenna between repeater reception antenna and the base station, does not have the echo interference problem to exist.Yet, because the coupling between transmitting antenna and the reception antenna (comprising multipath coupling and physical coupling), receiving terminal can be received the signal that oneself forwards, formation can be disturbed up to the strong echo of 30dB, when the repeater is arranged in the border of adjacent cells, must have the ability of automatic opposing monkey chatter.
Find through literature search prior art, Chinese patent application number is 02802280, name is called the patent of invention of " using the Echo Cancellation reference signal to carry out the method and apparatus of Echo Cancellation " in digital communication, use Echo Cancellation reference signal training signal to resist the multipath echo problem through particular design, but need take the valid data resource, to use pre-equalization subsystem at receiving terminal simultaneously, and be not suitable for using training sequence in digital multi-media broadcast direct broadcast station, so this invention can not solve the multipath echo coupled problem between the digital multi-media broadcast direct broadcast station dual-mode antenna.
Summary of the invention
The objective of the invention is to overcome deficiency of the prior art, propose a kind of digital multi-media broadcast direct broadcast station multipath echo removing method, make it utilize least mean-square error adaptive algorithm and intermediate frequency digital processing technology effectively to eliminate the interference problem that multipath echo brings.
The present invention is achieved through the following technical solutions, the present invention utilizes a self adaptation finite length filtering device to come analog digital multi-media broadcast direct broadcast station transmitting antenna to the coupling of the multipath between reception antenna channel, the tap coefficient of this self adaptation finite length filtering device utilize above-mentioned repeater to transmit by one and received signal between the least mean-square error adaptive algorithm of uncorrelated characteristic upgrade, after this self adaptation finite length filtering device filtering of transmitted reference signal process that directly coupling is come of transmitting antenna end, can simulate actual echo-signal well, therefore from received signal, deduct the interference that this analog echo signal can effectively be eliminated multipath echo; The entire process process is placed on 20 megahertz intermediate frequency processes and carries out, digital intermediate frequency signal is through becoming the complex baseband signal of low rate after Digital Down Convert and the 48 times of extractions, whole least mean-square error adaptive algorithm and self adaptation finite length filtering computation complexity have been simplified, thereby can be adapted to transmitting-receiving multipath coupling environment within 10 microseconds well, the processing time that whole multipath echo is eliminated thereby can not influence the performance of whole network within 20 microseconds.
It is as follows to the present invention includes concrete steps:
(1) signal that receives on the reception antenna is carried out rf filtering, and be down-converted to the intermediate frequency of 20M, utilize the analog to digital converter of 80M14 bit to carry out analog-to-digital conversion through the analog intermediate frequency signal behind the intermediate frequency filtering, obtain the intermediate frequency digital received signal of 20M, use the numerically-controlled oscillator of 20M that this digital intermediate frequency signal is downconverted to zero intermediate frequency then, and carry out 48 times down-sampling Filtering Processing, obtain the complex radical band digital signal x (n) of 1.66M;
(2) from analog of transmitting antenna end coupling, pass through rf filtering, and be down-converted to the intermediate frequency of 20M, utilize the analog to digital converter of 80M14 bit to carry out analog-to-digital conversion, obtain digital intermediate frequency signal y through the analog intermediate frequency signal behind the intermediate frequency filtering
IF, the numerically-controlled oscillator that uses 20M then is with this digital intermediate frequency signal y
IFDownconvert to zero intermediate frequency, and carry out 48 times down-sampling Filtering Processing, obtain the complex radical band digital reference signal y of 1.66M
n
(3) with above-mentioned complex radical band digital reference signal y
nSend into a self adaptation finite length filtering device, the echo-signal h that obtains simulating
Ty
n
(4) the complex radical band digital signal x (n) that receives is sent into the self adaptation finite length filtering device that constantly upgrades in time, from receive the complex digital baseband signal, deduct from the signal h of this self adaptation finite length filtering device output then
Ty
n, obtain error signal e (n);
(5) with complex radical band digital reference signal y
nAnd error signal e (n) sends into the least mean-square error estimator, estimates to be used for the tap coefficient h of self adaptation finite length filtering device in analogue echo path;
(6) the tap coefficient h number of self adaptation finite length filtering device is K according to the delay adjustments of maximum multipath echo, and the more new formula of tap coefficient h numerical value is
(7) error signal e (n) is carried out the control of automatic digital gain and conciliate correlation delay and handle, the time of delay is the τ microsecond, and making does not have correlation between the useful signal that receives on error signal and the reception antenna;
(8) will carry out 48 times up-sampling processing through the error signal that decorrelation postpones, reverting to speed is the zero intermediate frequency digital signal of 20M, the numerically-controlled oscillator that utilizes 20M then with this zero intermediate frequency digital signal up-conversion to the 20M digital intermediate frequency signal, again this digital intermediate frequency signal carried out the digital-to-analogue conversion of 80M16 bit thereafter, obtain corresponding 20M analog if signal, this analog if signal is simulated up-conversion and channel filtering processing, obtain radio frequency analog signal, at last resulting radio frequency analog signal is directly delivered to the transmitting antenna end.
Because the relation of the physical location between transmitting antenna and the reception antenna, add the reflection of upper ground surface and moving targets such as nearby buildings or automobile, the reception antenna end of digital multi-media broadcast direct broadcast station will be received very strong multipath echo interference signal, the method that the present invention puts forward can effectively be suppressed to these echoes the level more than the 30dB, to guarantee that whole single-frequency transmission network can operate as normal.
The elimination of whole echo parasitic feedback adopt one can the analog transmissions antenna and reception antenna between the self adaptation finite length filtering device of channel realize that the unit impulse response h of this filter can use related algorithm to estimate.Thereby giving multipath echo in the present invention offsets processing time-delay about one 20 microsecond of treatment system and makes that between the reference signal of the signal of emission again and feedback and the received signal be incoherent.In fact except the error signal e (n) that postpones, also comprise some other interference signals among the forward signal y (n), such as intermodulation item between the power amplification or adjacent-channel noise etc.
The present invention adopts the least mean-square error method to upgrade self adaptation finite length filtering device coefficient.Given input x (n) and output y (n), the target that the present invention handles is to make error signal e (n) minimize,
e(n)＝x(n)-h
Ty
n (1)
Y in the formula (1)
n=[y (n) y (n-1) Ly (n-K+1)]
TK is the length of self adaptation finite length filtering device, the tap coefficient h that K obtains too little then self adaptation finite length filtering device can not effectively simulate actual multipath echo channel, obtaining influences this convergence of algorithm speed too greatly again and takies more hardware resource, get 10 μ S * 20MHz=200 in the present invention, in the further optimizing process of algorithm, can reduce the tap number h of this self adaptation finite length filtering device again.
The more new formula of the self adaptation finite length filtering device tap coefficient among the present invention is:
The selection of convergence factor μ will be compromised between convergence rate and multipath echo elimination effect in the formula (2), convergence factor can be caught up with because the quick variation that Doppler and multipath reflection cause faster, cost is that self adaptation finite length filtering device tap coefficient estimated accuracy descends, on the contrary, slower convergence factor then can make because of the Doppler effect of formation such as wind and contain the composition of a lot of y (n) among the e (n), and then causes that whole echo eliminates the treatment system job insecurity.
In fact, the convergence effect depends on covariance matrix R
Yy=E (yy
*) eigenvalue distribute, it is best to restrain effect when all eigenvalues all equate, but R
YyGeneral is not full rank, and some eigenvalue can be near zero, and the convergence effect can be affected.Yet the actual signal that the present invention handles is a digital multimedia broadcasting signal, have good noise like character through the digital multimedia broadcasting signal after the ofdm system modulation, the least-mean-square error algorithm that is very suitable for low computation complexity is handled.
Description of drawings
Fig. 1 uses the digital multi-media broadcast direct broadcast station workflow diagram of the inventive method
Two-stage filtering extraction schematic diagram among Fig. 2 the present invention
Two-stage filtering hardware is realized schematic diagram among Fig. 3 the present invention
Self adaptation finite length filtering device operation principle schematic diagram among Fig. 4 the present invention
Digital Auto Gain control AGC principle schematic among Fig. 5 the present invention
Embodiment
Below embodiments of the invention are elaborated: present embodiment is that prerequisite is implemented with the technical solution of the present invention, provided detailed execution mode and concrete operating process, but protection scope of the present invention is not limited to following embodiment.
As shown in Figure 1, use the digital multi-media broadcast direct broadcast station of the inventive method to use directional antenna to receive needed multimedia digital broadcast signal, this received signal is sent to transponder main signal input port.The mirror image that the present invention uses a radio-frequency filter to suppress before the down-conversion disturbs, and re-uses frequency mixer filtered signal is changed to the intermediate frequency of 20MHz, uses high-order LC20M intermediate-frequency filter to come the energy of the most of monkey chatter of filtering simultaneously.Received signal has been submerged in the multipath echo interference signal that is up to 30dB, so the design of frequency converter and intermediate-frequency filter must be able to guarantee to have less distortion and bigger dynamic range in the channel width before signal carries out digitlization.
Present embodiment adopts the analog to digital converter (ADC) of 14 80MHz to realize the digitized process of whole 20M analog intermediate frequency signal, has the signal to noise ratio of 90dB at least to guarantee whole signal within the Nyquist Bandwidth of 80MHz.The effective bandwidth of actual digital multimedia broadcasting signal is 1.536MHz.
Carry out after the digitlization, the present invention utilizes numerically-controlled oscillator (NCO) that this digital signal down variable frequency is arrived the zero intermediate frequency complex baseband signal, obtains homophase and quadrature component.Then the complex baseband signal that this homophase and quadrature component are formed carries out the extraction of filtering and 48 times, signal rate is dropped to 1.66MHz, can carry out self adaptation like this estimates and Filtering Processing multipath echo interference problem, the present invention gives the transition band of signal filtering and has only 176KHz, therefore the whole filter transition band is very precipitous, can obtain complex radical band digital signal x (n) like this.
The radiofrequency signal that to come from transmitting antenna coupling through with the same processing of said process after obtain complex radical band reference digital signal y
n, simultaneously with y
nSend into self adaptation finite length filtering device, obtain filtered analogue echoes signal h
Ty
n, from complex radical band digital signal x (n), deduct this analog echo signal h
Ty
n, obtaining error signal e (n), this error signal has just been eliminated the useful signal of echo.
Further handle through the useful signal e (n) after the elimination of base band echo by AGC (digital Auto Gain control), the purpose of carrying out the digital gain control and treatment is to guarantee the nil symbol unit controls of whole multimedia digital broadcast signal, does not influence the networking function of whole system.Then will carry out decorrelation and postpone the τ microsecond, and make the processing time-delay of whole echo cancellation system be controlled at 20 microseconds through the signal after the digital gain control and treatment.The digital-to-analogue conversion processing that the last intermediate frequency up-conversion that will carry out 20MHz again through the signal after postponing and 80MHz are 16.The entire process system adopts a FPGA (field programmable gate array device) to realize.
Whole signal level can realize real-time monitoring by an Embedded microprocessor, so that the working condition of control figure gain controlling treatment circuit.If the generation abnormal conditions, during such as signal overloading, the output of transponder will reduce; The parameter of particular importance, for example the adjustment of the length of self adaptation finite length filtering device and convergence factor can effectively be adjusted by the USB serial ports.
Employing the inventive method can effectively be suppressed at whole multipath echo the level more than the 30dB.
As shown in Figure 2,48 times of down-sampling Filtering Processing of complex radical band data subsystem, the realization that is mainly follow-up base band least-mean-square error algorithm provides good rate interface and the outer inhibition ability of band, the actual effective bandwidth of considering signal is 1.536M, the present invention moves whole signal to zero intermediate frequency and rounds a base band speed is 1.66M, in order to realize good antijamming capability, the system's transition band width that is provided with only is 176K, and system will provide the anti-monkey chatter of 40dB at least and 48 times rate transition ability.
In order to reduce the computation complexity that whole digital multi-media broadcast direct broadcast station multipath echo is eliminated, the present invention adopts the two-stage filtering extraction to carry out the down-sampling Filtering Processing: first order filtering extraction provides 8 times rate transition ability, the first finite length filtering device h
1(n) damascene method such as employing design, design objective is sample frequency 80M, band connection frequency 768KHz, stopband cut-off frequency 2MHz, the first finite length filtering device h that designs
1(n) be 128 rank, suppress ability through the stopband that 60dB can be provided behind 16 bit quantizations; Second level filtering extraction provides 6 times rate transition ability, the second finite length filtering device h
2(n) damascene method such as employing design, design objective is that sample frequency 10M, band connection frequency are that 768KHz, stopband cut-off frequency are 944KHz, the second finite length filtering device h that designs
2(n) be 112 rank, suppress ability through the stopband that 60dB can be provided behind 16 bit quantizations.
As shown in Figure 3, the field programmable gate array device of 48 times of down-sampling Filtering Processing of complex radical band data system is realized for convenience, the present invention adopts heterogeneous structure to handle the two-stage filtering extraction: first order filtering extraction is divided into 8 the tunnel to be handled, the data that use on each road differ a clock each other, every road all is through 8 times of extractions, therefore the data transfer rate on every road all is 10M, and the first finite length filtering device coefficient on 128 rank that first order filtering extraction is designed is according to h
1i(n)=h
1(8n+i), i=0, K, 7 handle the multinomial filter coefficient data that can obtain each road; Second level filtering extraction is divided into 6 the tunnel to be handled, the data that use on each road differ a clock each other, therefore every road all is through 6 times of extractions, and the data transfer rate on every road all is 1.66M, and the second finite length filtering device coefficient on 112 rank that second level filtering extraction is designed is according to h
2i(n)=h
2(6n+i), i=0, K, 5 handle the multinomial filter coefficient data that can obtain each road, are 128 * 80 * 10 through the multiplication number of times of carrying out in the per second after the bi-level treatment like this
6/ 8+112 * 10 * 10
6/ 6=1.4667e+009.
As shown in Figure 4, through the 1.66M complex radical band reference signal y after the processing of reduction of speed rate
nThrough a self adaptation finite length filtering device h that 200 tap coefficients are arranged, output signal h
Ty
n, the renewal of this self adaptation finite length filtering device tap coefficient according to
Carry out.
As shown in Figure 5, DMB multipath echo of the present invention is eliminated to handle and is used the digital Auto Gain control unit that is directly embedded in the field programmable gate array device to improve the resolving power of output DAC (digital to analog converter) output and necessary nil symbol unit in the forward signal is provided, in-phase component EI (n) and quadrature component EQ (n) through the digital error signal after the echo elimination at first handle through automatic numerical control gain adjustment, adjusted these two components are admitted to a conjugation numeral rotary calculator amplitude of carrying out and extract, the amplitude and the thresholding N that extract are subtracted each other, then the error signal that obtains is carried out the integration loop filtering that adds up and handle, and utilize the signal of filtering output to adjust gain coefficient automatically.In order to recover the necessary nil symbol unit of digital multimedia broadcasting system, the present invention will compare through amplitude and adjustable low threshold G that conjugation numeral rotary calculator extracts simultaneously, if this amplitude is lower than this thresholding, then two components of inphase quadrature are forced simultaneously zero setting to be handled.Through obtaining in-phase signal I (n) and orthogonal signalling Q (n) after the digital Auto Gain control and treatment, thresholding G and N all adjust by the USB serial ports.
Claims (8)
1, a kind of digital multi-media broadcast direct broadcast station multipath echo removing method is characterized in that concrete steps are:
(1) signal that receives on the reception antenna is carried out rf filtering, and be down-converted to the intermediate frequency of 20M, utilize the analog to digital converter of 80M14 bit to carry out analog-to-digital conversion through the analog intermediate frequency signal behind the intermediate frequency filtering, obtain the intermediate frequency digital received signal of 20M, use the numerically-controlled oscillator of 20M that this digital intermediate frequency signal is downconverted to zero intermediate frequency then, and carry out 48 times down-sampling Filtering Processing, obtain the complex radical band digital signal x (n) of 1.66M;
(2) from analog of transmitting antenna end coupling, pass through rf filtering, and be down-converted to the intermediate frequency of 20M, utilize the analog to digital converter of 80M14 bit to carry out analog-to-digital conversion, obtain digital intermediate frequency signal y through the analog intermediate frequency signal behind the intermediate frequency filtering
IF, the numerically-controlled oscillator that uses 20M then is with this digital intermediate frequency signal y
IFDownconvert to zero intermediate frequency, and carry out 48 times down-sampling Filtering Processing, obtain the complex radical band digital reference signal y of 1.66M
n
(3) with complex radical band digital reference signal y
nSend into a self adaptation finite length filtering device, the echo-signal h that obtains simulating
Ty
n
(4) the complex radical band digital signal x (n) that receives is sent into the self adaptation finite length filtering device that upgrades in time, from receive complex radical band digital signal, deduct then from the signal h of this self adaptation finite length filtering device output
Ty
n, obtain error signal e (n), wherein h
TTransposed matrix for the tap coefficient h of self adaptation finite length filtering device;
(5) with complex radical band digital reference signal y
nAnd error signal e (n) sends into the least mean-square error estimator, estimates to be used for the tap coefficient h of self adaptation finite length filtering device in analogue echo path;
(6) the tap coefficient h number of self adaptation finite length filtering device is K according to the delay adjustments of maximum multipath echo, and the more new formula of tap coefficient h numerical value is
Wherein μ is a convergence factor;
(7) error signal e (n) is carried out the control of automatic digital gain and conciliate correlation delay and handle, the time of delay is the τ microsecond, and making does not have correlation between the useful signal that receives on error signal and the reception antenna;
(8) will carry out 48 times up-sampling processing through the error signal that decorrelation postpones, reverting to speed is the zero intermediate frequency digital signal of 20M, the numerically-controlled oscillator that utilizes 20M then with this zero intermediate frequency digital signal up-conversion to the 20M digital intermediate frequency signal, again this digital intermediate frequency signal carried out the digital-to-analogue conversion of 80M16 bit thereafter, obtain corresponding 20M analog if signal, this analog if signal is simulated up-conversion and channel filtering processing, obtain radio frequency analog signal, at last resulting radio frequency analog signal is directly delivered to the transmitting antenna end.
2, digital multi-media broadcast direct broadcast station multipath echo removing method according to claim 1, it is characterized in that, in the step (1), described down-sampling Filtering Processing, adopt the two-stage filtering extraction to carry out: first order filtering extraction provides 8 times rate transition ability, the first finite length filtering device h
1(n) damascene method such as employing design, it is sampled as frequency 80M, band connection frequency is that 768KHz, stopband cut-off frequency are 2MHz, the first finite length filtering device h
1(n) be 128 rank, suppress ability through the stopband that 60dB is provided behind 16 bit quantizations; Second level filtering extraction provides 6 times rate transition ability, the second finite length filtering device h
2(n) damascene method such as employing design, its sample frequency is that 10M, band connection frequency are that 768KHz, stopband cut-off frequency are 944KHz, the second finite length filtering device h
2(n) exponent number is 112 rank, suppresses ability through the stopband that 60dB is provided behind 16 bit quantizations.
3, digital multi-media broadcast direct broadcast station multipath echo removing method according to claim 2, it is characterized in that, described two-stage filtering extraction, adopt heterogeneous structure to handle: first order filtering extraction is divided into parallel 8 the tunnel, the data that use on each road differ a clock each other, every road all is through 8 times of extractions, and the data transfer rate on every road all is 10M, and the first finite length filtering device coefficient on 128 rank that first order filtering extraction is designed is according to h
1i(n)=h
1(8n+i), i=0 ..., 7 handle the multiphase filter coefficient data that obtains each road; Second level filtering extraction is divided into 6 the tunnel to be handled, and the data that use on each road differ a clock each other, and every road all is through 6 times of extractions, and the data transfer rate on every road all is 1.66M, and the second finite length filtering device coefficient on 112 rank that second level filtering extraction is designed is according to h
2i(n)=h
2(6n+i), i=0 ..., 5 handle each road multiphase filter coefficient data of acquisition.
4, digital multi-media broadcast direct broadcast station multipath echo removing method according to claim 1, it is characterized in that, in the step (7), described automatic digital gain control, be specially: use the digital Auto Gain control that is directly embedded in the field programmable gate array device to improve the resolving power of output digital to analog converter and necessary nil symbol unit in the forward signal is provided, in-phase component EI (n) and quadrature component EQ (n) through the digital error signal after the echo elimination at first handle through the numerical control gain adjustment, adjusted these two components are admitted to a conjugation numeral rotary calculator amplitude of carrying out and extract, the amplitude and the thresholding N that extract are subtracted each other, then the error signal that obtains is carried out the integration loop filtering that adds up and handle, and utilize the signal of filtering output to adjust gain coefficient automatically.
5, digital multi-media broadcast direct broadcast station multipath echo removing method according to claim 4 is characterized in that, in the step (7), the thresholding N of digital Auto Gain control adjusts by the USB serial ports.
6, digital multi-media broadcast direct broadcast station multipath echo removing method according to claim 4, it is characterized in that, to compare through amplitude and adjustable thresholding G that conjugation numeral rotary calculator extracts, to recover the necessary nil symbol unit of digital multimedia broadcasting system, amplitude is lower than thresholding G, then two components of inphase quadrature are forced simultaneously zero setting to be handled, through obtaining in-phase signal I (n) and orthogonal signalling Q (n) after the digital Auto Gain control and treatment.
7, digital multi-media broadcast direct broadcast station multipath echo removing method according to claim 6 is characterized in that, the thresholding G of digital Auto Gain control adjusts by the USB serial ports.
8, digital multi-media broadcast direct broadcast station multipath echo removing method according to claim 1 is characterized in that, the processing time-delay that whole multipath echo is eliminated is 20 microseconds.
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| US8184737B2 (en) * | 2007-11-27 | 2012-05-22 | Korea Advanced Institute Of Science And Technology | Echo cancellation and echo channel estimation system using multiple antennas |
| CN101483453B (en) * | 2008-04-16 | 2012-10-10 | 北京创毅视讯科技有限公司 | Echo cancellation device of mobile multimedia system repeater and echo cancellation method |
| CN101312372B (en) * | 2008-05-12 | 2013-01-02 | 北京创毅视讯科技有限公司 | Echo eliminator and echo eliminating method |
| CN101640555B (en) * | 2008-07-30 | 2012-09-05 | 福建三元达通讯股份有限公司 | Method for designing repeater echo canceller based on combined filter |
| CN101359956B (en) * | 2008-09-12 | 2011-04-20 | 北京创毅视讯科技有限公司 | Repeater |
| CN102065033B (en) * | 2010-11-03 | 2013-11-06 | 三维通信股份有限公司 | Repeater with ICS function and implementation method thereof |
| CN102420621B (en) * | 2011-11-16 | 2014-10-08 | 北京华力创通科技股份有限公司 | Method and device for suppressing out-of-band interference of digital signals |
| CN102944885B (en) * | 2012-11-19 | 2014-07-09 | 中国人民解放军国防科学技术大学 | Method and device for simulating multi-channel consistency by satellite navigation signal |
| CN103117794B (en) * | 2013-03-11 | 2015-11-25 | 福建京奥通信技术有限公司 | A kind of radio frequency choosing band repeater of anti-self-excitation interference and the method for minimizing self-excitation interference |
| CN104735006B (en) * | 2015-03-12 | 2018-11-13 | 电子科技大学 | A kind of direct intermediate-frequency channel method based on weighted superposition |
| CN104735007B (en) * | 2015-03-12 | 2019-02-15 | 电子科技大学 | The unconfined direct intermediate-frequency channel method of a kind of pair of centre frequency |
| CN109245815B (en) * | 2018-08-02 | 2021-08-10 | 中山大学 | Method and system for determining transmitting signal of repeater |
| CN111092644A (en) * | 2019-12-10 | 2020-05-01 | 重庆邮电大学 | Echo suppression system and method for DMB common-frequency repeater |
| CN114024567B (en) * | 2021-10-27 | 2023-05-09 | 中国电子科技集团公司第三十六研究所 | Multi-tap delay circuit and design method thereof |
| CN116359871B (en) * | 2023-03-24 | 2024-01-19 | 上海毫微太科技有限公司 | Signal processing method and image acquisition equipment |
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