A high-precision time delay estimation method in complex electromagnetic environment

Abstract

The present invention discloses a high-precision delay estimation method in a complex electromagnetic environment, comprising the following steps: S1. The signal transmitter adds a cyclic suffix and a synchronization sequence to the end of the signal obtained by OFDM modulation of the training sequence, and performs framing and up-conversion to obtain a radio frequency transmission signal and transmit it; S2. The signal receiver sequentially performs down-conversion and time coarse synchronization on the received signal to obtain a received signal, and estimates and compensates for the frequency offset; S3. For the received signal after coarse time-frequency synchronization, the signal receiver performs conjugate multiplication of the training sequence of the received signal with the local training sequence through FFT transformation, and performs FFT time domain windowing on the result; S4. Select two equal segments before and after the windowed result to perform conjugate multiplication, accumulation, phase angle calculation, and delay calculation operations, and complete the operation of high-precision delay estimation of the data. The present invention effectively improves the accuracy of delay estimation in a complex electromagnetic environment and ensures the accuracy of received data sampling.

Description

Technical Field

[0001] The invention relates to time synchronization, and in particular to a high-precision time delay estimation method under a complex electromagnetic environment. Background Art

[0002] In modern wireless communications, time synchronization accuracy plays a decisive role in whether the signal can be correctly demodulated. Integer multiple sampling rate delay estimation can only obtain rough time delay, and the delay accuracy is not high. If high-precision delay estimation and synchronization are not performed, the communication signal will have a phase deviation, which will reduce the final communication signal demodulation accuracy and affect the communication quality. The existing high-precision delay estimation method is easily affected by multipath and frequency deviation, and almost loses the ability to estimate delay in complex electronic environments. It has a very poor effect in communication systems with high time synchronization accuracy.

[0003] Multipath and noise can cause the performance of receiver time synchronization to deteriorate sharply, greatly reducing the communication quality. Existing high-precision time synchronization methods only preliminarily eliminate the influence of noise through accumulation, resulting in insufficient delay estimation performance. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a high-precision delay estimation method in a complex electromagnetic environment, which effectively improves the accuracy of delay estimation in a complex electronic environment and provides conditions for time synchronization in a complex electronic environment.

[0005] The purpose of the present invention is achieved through the following technical solution: A high-precision delay estimation method in a complex electromagnetic environment comprises the following steps:

[0006] S1. The signal transmitter adds a cyclic suffix and a synchronization sequence to the end of the signal obtained by OFDM modulation of the training sequence, and after framing and up-conversion, obtains the RF transmission signal and transmits it;

[0007] S2. The signal receiver sequentially down-converts and coarsely synchronizes the received signal to obtain the received signal, and estimates and compensates for the frequency offset;

[0008] S3. For the received signal after coarse time-frequency synchronization, the signal receiver multiplies the training sequence of the received signal by the FFT transform and the conjugate of the local training sequence, and performs FFT time-domain windowing on the result;

[0009] S4. Select two equal segments before and after the windowed result to perform conjugate multiplication, accumulation, phase angle calculation, and delay calculation operations to complete the operation of high-precision delay estimation of the data.

[0010] The beneficial effects of the present invention are as follows: the method proposed by the present invention effectively improves the accuracy of delay estimation in a complex electromagnetic environment, and provides conditions for time synchronization in a complex electronic environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a flow chart of the method of the present invention;

[0012] Figure 2 This is the schematic diagram of high-precision delay estimation in complex electronic environments;

[0013] Figure 3 It is a high-precision delay estimation process in complex electronic environments;

[0014] Figure 4 It is the performance simulation diagram of the present invention and the traditional method;

[0015] Figure 5 It is a performance simulation diagram of whether the present invention adds the time domain windowing function;

[0016] Figure 6 This is a performance simulation diagram of the present invention with or without adding a cyclic suffix. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0018] like Figure 1 As shown, a high-precision delay estimation method in a complex electromagnetic environment includes the following steps:

[0019] S1. The signal transmitter adds a cyclic suffix and a synchronization sequence to the end of the signal obtained by OFDM modulation of the training sequence, and after framing and up-conversion, obtains the RF transmission signal and transmits it;

[0020] S101. The local training sequence is a pseudo-random sequence x(n) with a length of N and a value of ±1. After OFDM modulation, a cyclic suffix with a length of m is added to the end. A synchronization sequence with a length of n is added to the frame header of each frame. The synchronization sequence is divided into two repeated GOLD sequences in the time domain, and then framed, up-converted, and transmitted through radio frequency. The expression of the transmitted signal f(t) is obtained as follows:

[0021]

[0022] Among them, C(t) is the framed data, f c is the center frequency of the RF modulation.

[0023] S2. The signal receiver sequentially down-converts and coarsely synchronizes the received signal to obtain the received signal, and estimates and compensates for the frequency offset;

[0024] Assume that the signal R(t) received by the receiver is expressed as:

[0025]

[0026] Among them, ω d is the Doppler frequency shift, T is the delay, and n(t) is the Gaussian noise.

[0027] The received signal R(t) is cached, and then down-converted and roughly synchronized in time and frequency. The time coarse synchronization uses the time domain sliding correlation algorithm to generate frame synchronization information. During the frequency coarse synchronization, the frequency deviation of the received signal caused by the Doppler effect is estimated and offset, the synchronization sequence is extracted from the signal after the time coarse synchronization, and the two equal-length data before and after the synchronization sequence are conjugated and multiplied, and then the obtained product is accumulated and dephased, and the frequency difference is estimated, and then compensated to the received signal;

[0028] The received data R after coarse time-frequency synchronization s (t), its expression is:

[0029]

[0030] Among them, A0 is the main diameter amplitude, A n is the amplitude of each multipath, τ is the fractional delay, τ<T s , T s is the symbol period, τ n is the multipath delay, and Δω is the residual frequency offset.

[0031] S3. For the received signal after coarse time-frequency synchronization, the signal receiver multiplies the training sequence of the received signal by the FFT transform and the conjugate of the local training sequence, and performs FFT time-domain windowing on the result;

[0032] S301. First, perform FFT transformation to obtain the received data F(t-τ) in the frequency domain, which is expressed as:

[0033]

[0034] Where N[ω] is the FFT transform of n(t);

[0035] The received signal after transform domain is conjugate-multiplied with the local sequence, and the obtained signal X[ω] is:

[0036]

[0037] in,

[0038] S302. Perform IFFT transformation on the conjugate multiplied signal to the time domain to obtain a time domain signal x(t):

[0039]

[0040] To suppress noise and multipath, time domain windowing is performed to obtain the signal x1(t):

[0041] x1(t)=A0δ(t-τ)+w1(t)

[0042] Where w1(t) is the windowed noise signal, and then the signal is transformed by FFT to obtain the frequency domain signal X1(ω):

[0043] X1[ω]=A0e -j(ω-Δω)τ +W1[ω]

[0044] Where W1[ω] is the windowed noise frequency domain signal.

[0045] S4. Select two equal segments before and after the windowed result to perform conjugate multiplication, accumulation, phase angle calculation, and delay calculation operations to complete the operation of high-precision delay estimation of the data.

[0046] S401. Assuming that the length of each FFT is N, since some sequences have phase ambiguity, we take the length of N / 4 between the first and last segments for conjugate multiplication. For example, if the FFT length is 2048, then select the sequence [257:768] in the first 1024 data and the sequence [1281:1793] in the last 1024 data for conjugate multiplication to obtain Q[ω], which is expressed as:

[0047]

[0048] X 1,n [ω], X 1,n+L [ω] represents two equal pieces of data obtained by conjugate multiplication.

[0049] Among them, Δω L is the phase difference between the previous and next sequences, and the fractional delay τ is calculated by accumulating the phase angle of Q[ω]. τ is the fractional delay mentioned in step S2, which represents the delay between the local training sequence and the transmission sequence at the receiving end. Its expression is:

[0050]

[0051] Among them, ∠ is the phase angle.

[0052] In the example of this application, the working principle is as follows Figure 2 As shown in the figure, the high-precision time synchronization processing flow of the communication system signal is as follows Figure 3As shown. After baseband signal processing, the signal source is up-converted and passes through the Rayleigh channel and AWGN channel. The receiver receives the signal and performs down-conversion, coarse time-frequency synchronization, and high-precision delay estimation in sequence to complete the high-precision delay estimation of the signal. Using MATLAB tools, the performance of the high-precision time synchronization algorithm proposed in the present invention is simulated and verified in the presence of frequency offset and multipath delay. The simulation parameters are set as follows:

[0053]

[0054] Figure 4 The delay estimation error is simulated with the change trend of signal-to-noise ratio, and the performance is compared with that of the traditional delay estimation method. It can be found that with the increase of signal-to-noise ratio, the delay estimation error of this method is constantly decreasing. Compared with the traditional frequency offset estimation method, it can be found that the traditional method almost loses the delay estimation ability, and this scheme can still perform high-precision time estimation well, which verifies the advancement and effectiveness of this delay estimation method. Figure 5 The variation trend of delay estimation error with signal-to-noise ratio is simulated and compared with the performance of removing the multipath suppression module. It can be found that under low signal-to-noise ratio conditions, the estimation error of this scheme with the multipath suppression module added is significantly lower than that of the scheme without the multipath suppression module, and the difference between the two is small under high signal-to-noise ratio. Figure 6 The variation trend of delay estimation error with signal-to-noise ratio is simulated and compared with the performance without adding cyclic suffix. It can be seen that the delay estimation error with adding cyclic suffix is ​​generally better than that without adding cyclic suffix.

[0055] In summary, for systems communicating in complex electronic environments, this paper proposes a new high-precision delay estimation method in complex electromagnetic environments, which effectively improves the time synchronization accuracy in complex electromagnetic environments and ensures the accuracy of delay estimation. The simulation results preliminarily verify the effectiveness and feasibility of this method.

[0056] The present invention has been described in detail herein by way of specific embodiments, and the description of the above embodiments is provided to enable those skilled in the art to make or apply the present invention, and various modifications of these embodiments will be readily understood by those skilled in the art. The present invention is not limited to these examples, or certain aspects thereof. The scope of the present invention is described in detail by the appended claims.

[0057] The above description shows and describes a preferred embodiment of the present invention, but as mentioned above, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the invention concept described herein through the above teachings or the technology or knowledge of the relevant field. And the changes and modifications made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A high-precision delay estimation method in a complex electromagnetic environment, characterized by: The following steps are involved: S1. The signal transmitter adds a cyclic suffix and a synchronization sequence to the end of the signal obtained by OFDM modulation of the training sequence, and after framing and up-conversion, obtains the RF transmission signal and transmits it; S2. The signal receiver sequentially down-converts and coarsely synchronizes the received signal to obtain the received signal, and estimates and compensates for the frequency offset; S3. For the received signal after coarse time-frequency synchronization, the signal receiver multiplies the training sequence of the received signal by the FFT transform and the conjugate of the local training sequence, and performs FFT time-domain windowing on the result; S301. First, perform FFT transformation to obtain the received data F(t-τ) in the frequency domain, which is expressed as: Where N[ω] is the FFT transform of n(t); The received signal after transform domain is conjugate-multiplied with the local sequence, and the obtained signal X[ω] is: in, S302. Perform IFFT transformation on the conjugate multiplied signal to the time domain to obtain a time domain signal x(t): To suppress noise and multipath, time domain windowing is performed to obtain the signal x1(t): x1(t)=A0δ(t-τ)+w1(t) Where w1(t) is the windowed noise signal, and then the signal is transformed by FFT to obtain the frequency domain signal X1(ω): X1[ω]=A0e -j(ω-Δω)τ +W1[ω] Where W1[ω] is the windowed noise frequency domain signal; S4. Select two equal segments before and after the windowed result to perform conjugate multiplication, accumulation, phase angle calculation, and delay calculation operations to complete the operation of high-precision delay estimation of the data.

2. According to the high-precision delay estimation method in a complex electromagnetic environment according to claim 1, it is characterized by: The step S1 includes: the local training sequence is a pseudo-random sequence x(n) with a length of N and a value of ±1, which is modulated by OFDM and has a cyclic suffix with a length of m added to the end, and a synchronization sequence with a length of n is added to the frame header of each frame. The synchronization sequence is divided into two repeated GOLD sequences in the time domain, and then framed, up-converted, and transmitted through radio frequency, and the expression of the transmission signal f(t) is obtained as follows: Among them, C(t) is the framed data, f c is the center frequency of the RF modulation.

3. The high-precision delay estimation method in a complex electromagnetic environment according to claim 1 is characterized in that: The step S2 comprises the following sub-steps: Assume that the signal R(t) received by the receiver is expressed as: Among them, ω d is the Doppler frequency shift, T is the delay, and n(t) is the Gaussian noise; The received signal R(t) is cached, and then down-converted and roughly synchronized in time and frequency. The time coarse synchronization uses the time domain sliding correlation algorithm to generate frame synchronization information. The frequency deviation caused by the Doppler effect of the received signal is estimated and offset during the frequency coarse synchronization. The synchronization sequence is extracted from the signal after the time coarse synchronization, and the two equal-length data before and after the synchronization sequence are conjugated and multiplied. The obtained products are then accumulated and dephased to estimate the frequency difference value, which is then compensated to the received signal. The received data R after coarse time-frequency synchronization s (t), its expression is: Among them, A0 is the main diameter amplitude, A n is the amplitude of each multipath, τ is the fractional delay, τ<T s , T s is the symbol period, τ n is the multipath delay, and Δω is the residual frequency offset.

4. According to the high-precision delay estimation method in a complex electromagnetic environment according to claim 1, the step S4 comprises: Assume that the length of each FFT is N, divide the entire length into two segments, take the middle N / 4 length in each segment, and perform conjugate multiplication to obtain Q[ω], which is expressed as: X 1,n [ω], X 1,n+L [ω] represents two equal segments of data obtained by conjugate multiplication; Among them, Δω L is the phase difference between the previous and next sequences. The fractional delay τ is calculated by accumulating the phase angle of Q[ω]. τ is the fractional delay mentioned in step S2, which represents the delay between the local training sequence and the transmission sequence at the receiving end. Its expression is: Among them, ∠ is the phase angle.

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