CN111614593B - Synchronization method for resisting single-tone interference of OFDM system - Google Patents
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- H04L27/26—Systems using multi-frequency codes
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Abstract
The invention discloses a method for single-tone interference resisting synchronization under an OFDM system, which comprises the following steps: 1) Carrying out filtering processing in a sliding window on the received signal to filter the influence of direct current interference; 2) Before receiving effective signals, counting average powers of interference and noise, and estimating the amplitude of interference noise; storing, calculating the current signal-to-interference-and-noise ratio, feeding back to the transmitting end, and adjusting the power of the transmitting end to meet the requirements of system synchronization and minimum error rate; 3) Filtering a peak value calculated by a single tone signal according to the relationship between the signal energy of the auxiliary data AGC and the position of a relevant peak value, estimating a synchronous position, FFT (fast Fourier transform algorithm) and channel estimation, and calculating the frequency point position of the single tone interference signal through a channel coefficient; 5) Entering a synchronous tracking stage, and estimating a synchronous position; the invention solves the problems of error synchronization and synchronization loss caused by direct current offset interference and single tone interference in the bandwidth of the OFDM system, reduces the false alarm probability of synchronization and improves the system performance.
Description
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a synchronization method for resisting single-tone interference of an OFDM system.
Background
Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier modulation scheme that overcomes frequency selective fading of the channel by reducing and eliminating the effects of inter-symbol interference. OFDM is very sensitive to synchronization errors, and especially in multipath fading channels, symbol timing errors can destroy orthogonality between subcarriers, causing severe inter-symbol interference (ISI).
The synchronization tasks of the OFDM system comprise time synchronization and carrier frequency synchronization, the time synchronization aims to determine the starting position of an OFDM symbol so as to carry out multi-carrier demodulation on data, and the carrier frequency synchronization aims to solve the problems of signal amplitude attenuation and subcarrier spacing interference caused by frequency inconsistency between a transmitter and a receiver.
Many documents already analyze and research timing synchronization methods of OFDM, but the existing methods lack measures against interference, and the synchronization false alarm rate is too high in an interference environment, resulting in serious degradation of system communication performance.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a synchronization method for OFDM system to resist single-tone interference, which solves the problem that the in-band single-tone interference in the system affects synchronization.
The invention is realized by the following technical scheme:
a synchronization method for OFDM system to resist single tone interference includes,
after anti-interference processing is carried out on a received radio frequency signal by modules of IQ offset interference filtering, power adjustment, synchronous correlation, interference point searching, interference signal remodeling, filtering and the like, the influence of interference on synchronization is eliminated, and a correct synchronization position is estimated.
In the IQ offset interference filtering, in the initial blind synchronization process of the system, the time domain filtering processing is carried out on the radio frequency signal received by the receiver, the direct current offset interference component in the signal is removed, and the error correlation caused by the direct current offset interference is avoided;
the power adjustment is to count the average power of interference and noise in a coherent time before receiving an effective signal, estimate the amplitude of interference noise according to the power and store the amplitude; according to the total energy and the interference signal energy calculated in the synchronous correlation process, the signal to interference plus noise ratio is calculated and fed back to the transmitting end, and the power of the transmitting end is adjusted to meet the lowest requirements of the system synchronous probability and the bit error rate;
in the synchronous correlation, in the initial blind synchronization stage, a correlation measurement function is calculated, the position of a peak value is judged, the peak value is normalized to meet a normalization threshold condition, meanwhile, a synchronization condition is set according to the relation between the signal energy of the auxiliary data AGC and the position of the correlation peak value, the peak value caused by a single tone signal is filtered, and the synchronization position is correctly estimated;
searching the interference point, after the initial synchronization is successful, performing FFT (fast Fourier transform) and channel estimation calculation, calculating the total energy and average energy of a channel coefficient through the channel coefficient, determining the interference point according to the interference setting condition, calculating the frequency offset of the single-tone interference signal according to the interference point, and storing the frequency offset;
and the interference signal is reshaped and filtered, a synchronous tracking stage is entered, the reshaped single-tone interference signal is subtracted from the received signal, the interference of the single-tone signal to the synchronization process is reduced, and the synchronization position is estimated.
A method for synchronization of an OFDM system against single-tone interference, the method comprising:
step s1, establishing a sliding window, taking the data mean value in the window, subtracting the mean value of the time domain signal in the sliding window from the received radio frequency signal, filtering the interference caused by IQ amplitude deviation of the received signal,
wherein, in the process,
entering step s2, where the index is the subscript of the time domain signal in the sliding window, WL is the length of the established sliding window, r (n) is the received radio frequency signal, and n is the subscript of the received signal;
step s2, before receiving the effective signal, processing the signal r (n) at the receiving end,
where Tc is the coherence time of the energy statistics,
is a signal
K is the number of statistical energies. Taking the minimum value as the energy of the interference signal,
and calculates the amplitude of the interference signal,
entering step s3;
step s3, roughly calculating the signal-to-interference-and-noise ratio of the received signal, returning to the sending end for power adjustment, the concrete steps include,
in a synchronous correlation process, step s31, the total average energy of the signal is calculated,
where d is the delay length of the received signal,
if N is the length of the correlation window and fftsize is the length of FFT, go to step s32;
and step s32, calculating the signal to interference and noise ratio,
proceeding to step s33;
step s33, determining whether the current signal satisfies the system condition:
wherein, in the process,
is the error rate corresponding to the signal-to-interference ratio,
is the expected error rate of the system and,
a synchronization false alarm probability expected for the system; if the condition is met, entering step s4; otherwise, feeding back to the transmitting end, improving the signal power of the transmitting end, and entering the step s1;
step s4, entering a synchronization module for timing synchronization processing, specifically comprising,
step s41 of calculating a synchronization-related metric function
；
Step s42, the correlation peak is found,
the position of the synchronization position,
normalizing the peak value;
step s43, setting synchronous decision condition according to the position relation between the auxiliary data AGC energy and the related peak value, calculating the data ratio
，
，
Wherein,
for the energy at the position of the AGC,
in order to be the energy of the correlation,
which is the position of the AGC symbol, symLen is the AGC symbol length,
is the set synchronization decision condition. If the synchronization judgment condition is met, the synchronization is successful, and the step s5 is entered; otherwise abandon, enter step s1 again;
step s5, searching the position of the interference point, which comprises the following specific steps,
step s51, calculating a channel coefficient, H;
step s52, counting the total energy and the average energy in the frequency domain of the channel coefficients,
，
where Nc is the subcarrier length;
step s53, estimating the energy
Maximum value of
And the position is recorded,
；
step s54, calculating the number of sign bits of the total energy and the average energy respectively,
，
and calculating the difference:
；
step s55, setting an interference signal threshold value,
if it is determined that
If so, then an interference signal is present, and the interference position is calculated:
the interference frequency points are:
，
for subcarrier spacing, an interference phase coefficient is established:
，
DL is the time domain data length; if the condition is not met, no interference signal exists; entering step s6;
step s6, according to the estimated interference signal amplitude and phase position, the interference signal is reshaped,
wherein
In order to be able to measure the amplitude of the interference,
in order to disturb the phase of the signal,
，
counting the number of sampling points of the system, and entering a step s7;
step s7, the system enters a synchronous tracking stage, the interference signal is subtracted from the received signal,
wherein
，
counting the number of sampling points of the system; reducing single-tone interference of the received signal causes attenuation of amplitude and phase.
Drawings
FIG. 1 is a system process flow diagram of the present invention;
FIG. 2 illustrates a received signal of DC offset jammer;
FIG. 3 simultaneous correlation peaks under single-tone interference;
FIG. 4 is a relationship of sync correlation peak to energy under single tone interference;
FIG. 5 frequency domain interferer point location;
fig. 6 comparison of the pre-and post-synchronization correlation peaks for interference point cancellation.
Detailed Description
To make the objects and advantages of the present invention clearer, the present invention will be described in further detail with reference to the accompanying drawings and examples.
Referring to fig. 1, the specific implementation steps of the present invention are as follows:
in the synchronous correlation process, step 31, the total average energy of the signal is calculated,
wherein
，
，
；
step 32, calculating the signal to interference plus noise ratio,
as shown in fig. 3, under different sinr conditions, the degree of attenuation of the synchronization peak is different;
step 33, setting parameters:
is the expected error rate of the system and,
a synchronization false alarm probability expected for the system; judging whether the current signal meets the system condition:
if the condition is met, entering the step 4; otherwise, feeding back to the sending end, improving the signal power of the sending end, and entering the step 1;
step 41, calculating a metric function of synchronization correlation
；
In step 42, the correlation peak is found,
the position of the synchronization position is determined,
normalizing the peak value, wherein the threshold value of the normalized peak value is 0.6;
step 43, according to the position relationship between the auxiliary data AGC energy and the correlation peak, as shown in fig. 4, a synchronization decision condition is set
Calculating the data ratio
If the synchronization judgment condition is met, the synchronization is successful, and the step 5 is entered; otherwise abandon, enter step 1 again;
step 51, calculating a channel coefficient, H, as shown in fig. 5;
step 52, counting the total energy and average energy in the frequency domain of the channel coefficient,
，
wherein, in the process,
frequency domain subcarrier length;
step s53, estimating energy
The maximum value of (a) is,
and the position is recorded,
；
step s54, calculating the number of sign bits of the total energy and the average energy respectively,
，
and calculating the difference:
；
step s55, setting an interference signal threshold value,
if, if
If so, then an interference signal is present, and the interference position is calculated:
the interference frequency points are:
，
，
，
，
(ii) a If the condition is not met, no interference signal exists; entering step 6;
and step 6, the interference signal is reshaped,
wherein
In order to be able to measure the amplitude of the interference,
in order to disturb the phase of the signal,
，
entering step 7;
step 7, the system enters into the synchronous tracking stage, the interference signal is subtracted from the received signal, and the synchronous position is calculated by synchronous correlation, as shown in figure 6,
wherein, in the process,
，
。
in summary, the above description is only a preferred example of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. A synchronization method for OFDM system to resist single tone interference is characterized in that,
after anti-interference processing is carried out on a received radio frequency signal by an IQ offset interference filtering module, a power adjusting module, a synchronous correlation module, an interference point searching module and an interference signal reshaping and filtering module, the influence of interference on synchronization is eliminated, and a correct synchronization position is estimated;
the IQ offset interference filtering module is used for carrying out time domain filtering processing on the radio frequency signal received by the receiver in the initial blind synchronization process of the system, removing direct current offset interference components in the signal and avoiding error correlation caused by direct current offset interference;
the power adjusting module is used for counting the average power of interference and noise in a time period before receiving the effective signal, estimating the amplitude of the interference noise according to the power and storing the amplitude; according to the total energy and the interference signal energy calculated in the synchronous correlation process, the signal to interference plus noise ratio is calculated and fed back to the transmitting end, and the power of the transmitting end is adjusted to meet the lowest requirements of the system synchronous probability and the bit error rate;
the synchronous correlation module is used for calculating a correlation measurement function, judging the position of a peak value, carrying out normalization processing on the peak value to meet a normalization threshold condition, setting a synchronous condition according to the relation between the signal energy of the auxiliary data AGC and the position of the correlation peak value, filtering the peak value caused by a single tone signal, and correctly estimating the synchronous position;
the interference point searching module is used for performing FFT and channel estimation calculation after the initial synchronization is successful, calculating the total energy and the average energy of a channel coefficient through the channel coefficient, determining an interference point according to the interference setting condition, calculating the frequency offset of a single-tone interference signal according to the interference point and storing the frequency offset;
the interference signal reshaping and filtering module enters a synchronous tracking stage, and the signal is received, the reshaped single-tone interference signal is subtracted, the interference of the single-tone signal to the synchronization process is reduced, and the synchronization position is estimated.
2. The method of claim 1, wherein the time-domain filtering is performed by subtracting an average value of the time-domain signal in a sliding window from the received RF signal,
where i =0,1.. WL-1 is the subscript of the time domain signal within the sliding window, WL is the length of the established sliding window, r (n) is the received radio frequency signal, and n is the subscript of the received signal.
3. The method of claim 1, wherein the average power of the statistical interference and noise is processed for the signal r (n) at the receiving end before receiving the effective signal,
EI (k) represents an energy average value in a kth segment coherence time, tc is a coherence time of energy statistics, r' (n) is a conjugate of a signal r (n), and k is the number of statistical energies; taking the minimum value as the interference signal energy, min { EI k And calculates the amplitude of the interference signal,
4. the method of claim 1, wherein the adjusting the transmit end power comprises:
4.1 during the synchronous correlation process, calculating the total average energy of the signal,
wherein d is the delay length of the received signal, and N is the correlation window length;
4.2 calculating the signal-to-interference-and-noise ratio according to a formula,
4.3 according to the signal-to-interference-and-noise ratio, judging whether the system condition is met: { eta (sinr) n )≤BER th ，P(sinr n )≤P fn In which η (sinr) n ) For bit error rate, BER, corresponding to signal-to-interference ratio th Error rate, P, expected for the system fn A synchronization false alarm probability expected for the system; if the conditions are met, entering step 5; otherwise, feeding back to the transmitting end to improve the signal power of the transmitting end.
5. The method of claim 1, wherein the step of correctly estimating the synchronization position comprises the steps of:
5.1 computing the metric function R of the synchronization correlation n ；
5.2 find correlation Peak, maxCorr, synchronization position peak pos Normalizing the peak value;
5.3 setting synchronous decision condition according to the position relation of AGC energy and related peak value,
E agc ＝COrr engy (agc pos )，agc pos ＝peak pos symLen, whichIn, E agc For the energy at the AGC location, COrr engy For the associated energy, agc pos For the position of the AGC symbol, symLen is the AGC symbol length, corr th If the set synchronization judgment condition is met, the synchronization is successful; otherwise, discarding and re-entering the blind synchronization process.
6. The method of claim 1, wherein the step of calculating the frequency offset of the tone-interference signal comprises the steps of:
6.1 calculating channel coefficient, H;
6.2 calculate Total energy and average energy, H, in the channel coefficient frequency domain ET (k)＝|H k | 2 /H ave ，
Wherein N is c Is the subcarrier length;
6.3 calculation of H ET (k) Maximum value of (C), H ET_max And recording the position, H max_pos ；
6.4 calculating the sign digit of the total energy and the average energy respectively,
and calculating a difference:
6.5 setting the interference signal threshold, sbc th If Δ sbc.gtoreq.sbc th Then, there is an interference signal, and the interference position:
the interference frequency points are: if = I pos *Δf c ，Δf c For the subcarrier spacing, an interference phase coefficient is established: I.C. A exp ＝e j2πIfn N =0,1., DL-1, DL is the time domain data length; if the condition is not satisfied, there is no interfering signal.
7. The method of claim 1, wherein the reshaped tone interference signal is I n ＝LA m *I exp ＝LA m e j2πIfn Wherein, I n To reshape the mono interference signal, I exp For disturbing the phase coefficient, LA m 2 pi If interference phase, N =0,1 s -1。
8. The method of claim 1 wherein r (n) = r (n) -LA for synchronization of OFDM system to single-tone interference, synchronization tracking stage receiving end signal processing m e j2πIfn Where r (n) is the received RF signal, LA m 2 pi If interference phase, N =0,1 s -1。
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