CN106534016A - Communication timing synchronization method and device - Google Patents

Abstract

The invention provides a communication timing synchronization method and device, which are applied in a DFT-S-OFDM system. The communication timing synchronization method includes: obtaining the vector sum of the received signal on N paths of the transmitted signal through the fading channel, the transmitted signal is a normalized N-point sampled complex signal, and N is an integer power of 2; N points are calculated point by point Send the cross-correlation value of the received signal, determine the maximum cross-correlation value in the cross-correlation value; calculate the test statistic according to the value near the maximum cross-correlation value and the autocorrelation value of the received signal, and use the test statistic It is used to determine the threshold of the relevant timing synchronization, thereby determining the starting point of the communication frame. The technical solution of the present invention can determine the threshold of the test statistic for timing synchronization in the fading channel of the DFT-S-OFDM communication system, and then determine the starting point of the communication frame according to the threshold to realize the timing synchronization of the data frame.

Description

A communication timing synchronization method and device

technical field

The invention relates to a communication technology, in particular to a communication timing synchronization method and device.

Background technique

LTE (Long Term Evolution, long-term evolution) is a global common standard formulated by the 3GPP organization based on OFDMA technology, including FDD and TDD modes for paired spectrum and unpaired spectrum. The SC-FDMA (Single-Carrier Frequency Division Multiple Access, single-carrier frequency division address) adopted by LTE uplink is implemented by DFT-S-OFDM (Discrete Fourier Transform Spread OFDM) technology, which is based on OFDM (Orthogonal Frequency Division Multiplexing, Orthogonal Frequency Division Multiplexing Technology) IFFT (Inverse Fast Fourier Transform, Inverse Fast Fourier Transform) modulation is performed on the signal before DFT (Discrete Fourier Transform, Discrete Fourier Transform) expansion, so that the system transmits a time-domain signal , so that the PAPR (Peak to Average Power Ratio, peak to average power ratio) problem caused by the OFDM system sending frequency domain signals can be avoided. The synchronization process is very important in the wireless communication system. Once the synchronization error exceeds the tolerance range or the synchronization fails, the performance of data demodulation and decoding will be greatly reduced, and even the communication will fail. Accurate timing synchronization is the basic condition for the realization of DFT-S-OFDM transmission system. In the field of wireless communication, fading refers to the phenomenon that the amplitude of the received signal changes randomly due to the change of the channel, that is, signal fading. A channel that causes signal fading is called a fading channel. In recent years, there have been many research results on timing synchronization, typically the maximum likelihood (ML) method, matched filter method (Matched Filter), correlation synchronization method, etc., each of which has its own usage scenarios And advantages and disadvantages, mainly applicable to AWGN (Additive White Gaussian Noise, Additive White Gaussian Noise, Additive White Gaussian Noise) channel, but hardly applicable to fading channels.

In view of this, how to find a timing synchronization scheme that is also applicable in fading channels has become an urgent problem to be solved by those skilled in the art.

Contents of the invention

In view of the shortcomings of the prior art described above, the purpose of the present invention is to provide a communication timing synchronization method and device for solving the problem in the prior art that the timing synchronization scheme under DFT-S-OFDM cannot be applied in fading channels.

In order to achieve the above purpose and other related purposes, the present invention provides a communication timing synchronization method, which is applied in the DFT-S-OFDM system, and the communication timing synchronization method includes: acquiring the transmission signal The vector sum of received signals on N paths through a fading channel The sending signal is a normalized N-point sampling complex signal, that is, N is an integer power of 2; calculate the cross-correlation values of N sending and receiving signals point by point For the conjugate of the transmitted signal x _i , determine the maximum cross-correlation value R _yx (j) among the cross-correlation values; is the conjugate of the received signal y _i , the test statistic is calculated according to the value near the maximum cross-correlation value and the autocorrelation value of the received signal, and the test statistic is used to determine the threshold of correlation timing synchronization, thereby determining the communication frame starting point.

Optionally, the calculation method of the test statistic includes: performing a division operation on the accumulation sum of 15 values near the maximum cross-correlation value and the autocorrelation value, and the test statistic is the conjugate of the transmitted signal y _i .

Optionally, the communication frame includes a data frame or a control frame; the structure of the communication frame includes a preamble symbol, a cyclic prefix and a data part; the structure of the control frame includes a preamble symbol and a data part.

Optionally, the preamble symbol adopts a pseudo-random sequence with excellent correlation performance.

Optionally, the length of the leading symbol is 1024.

The present invention also provides a communication timing synchronization device, which is applied in the DFT-S-OFDM system, and the communication timing synchronization device includes: used to obtain the transmission signal The received signal on N paths through the fading channel The sending signal is a normalized N-point sampling complex signal, which has N is an integer power of 2; the maximum cross-correlation value determination unit is used to calculate the cross-correlation value of the transmitted signal and the received signal point by point For the conjugate of the transmitted signal x _i , determine the maximum cross-correlation value R _yx (j) in the cross-correlation values; the test statistic calculation unit is used to autocorrelate with the received signal according to the value near the maximum cross-correlation value The value computes a test statistic that is used to determine the threshold for relative timing synchronization and thus the start point of a communication frame.

Optionally, the calculation method of the test statistic based on the maximum cross-correlation value includes: according to the cumulative sum of 15 values near the maximum cross-correlation value and the received signal autocorrelation value Do division, test statistic is the conjugate of the received signal y _i .

Optionally, the communication frame includes a control frame and a data frame; the structure of the communication frame includes a preamble symbol, a cyclic prefix and a data part.

Optionally, the preamble symbol adopts a pseudo-random sequence with excellent correlation performance.

Optionally, the length of the leading symbol is 1024.

As mentioned above, a communication timing synchronization method and device of the present invention has the following beneficial effects: it can determine the threshold value of the test statistic for timing synchronization of the DFT-S-OFDM communication system in a fading channel, and then determine the communication timing according to the threshold value. The starting point of the frame realizes the timing synchronization of the data frame.

Description of drawings

FIG. 1 is a schematic flowchart of an embodiment of a communication timing synchronization method of the present invention.

FIG. 2 is a block diagram of an embodiment of the communication timing synchronization device of the present invention.

FIG. 3 is a schematic diagram of a CDF curve of a cumulative distribution function in an AWGN channel environment in the prior art.

FIG. 4 is a schematic diagram of a CDF curve of a cumulative distribution function in a fading channel environment in the prior art.

FIG. 5 is a schematic diagram of a CDF curve of an embodiment of the communication timing synchronization method of the present invention under a fading channel environment.

Component designation description

1 Communication timing synchronization device

11 Related signal acquisition unit

12 Maximum cross-correlation value determination unit

13 Test statistic calculation unit

S1～S3 steps

detailed description

Embodiments of the present invention are described below through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation modes, and various modifications or changes can be made to the details in this specification based on different viewpoints and applications without departing from the spirit of the present invention.

It should be noted that the diagrams provided in this embodiment are only schematically illustrating the basic idea of the present invention, and only the components related to the present invention are shown in the diagrams rather than the number, shape and shape of the components in actual implementation. Dimensional drawing, the type, quantity and proportion of each component can be changed arbitrarily during actual implementation, and the component layout type may also be more complicated.

The invention provides a communication timing synchronization method, which is applied in a DFT-S-OFDM system. Discrete Fourier Transform Extended Orthogonal Frequency Division Multiplexing (DFT-S-OFDM) technology has been adopted by 3GPP and is a single carrier modulation technology. As the uplink modulation scheme of the long-term evolution project (LTE), it has the advantages of low peak-to-average ratio (PAPR), which improves the power efficiency of the uplink and expands the coverage of the signal when the uplink power amplifier requirements are the same. , which is beneficial to the hardware implementation of the user terminal. The synchronization process is very important in the wireless communication system. Once the synchronization error exceeds the tolerance range or the synchronization fails, the performance of data demodulation and decoding will be greatly reduced, and even the communication will fail. Accurate timing synchronization is the basic condition for the realization of the DFT-S-OFDM transmission system. The timing synchronization method of the present invention is realized on the basis of the auxiliary sequence, and the application scene is relatively harsh, and it can adapt to the Doppler frequency caused by high-speed motion. shift. Uplink includes control link and data link. For the data link, the sending end first modulates the input data bit stream into constellation symbols through MPSK (Multiple Phase Shift Keying, multi-ary digital phase modulation, also known as multi-phase system), and then performs DFT changes of M points, subcarriers Mapping, and then perform N-point (N>M) IFFT changes (here, DFT-S-OFDM subcarrier mapping is done with 2 times upsampling, so N=2*M), and add a cyclic prefix CP. For the control link, DFT, subcarrier mapping and IFFT changes are also performed to generate DFT-S-OFDM symbols, but no cyclic prefix is added, and finally framing is performed In one embodiment, as shown in Figure 1, the communication timing is synchronized Methods include:

Step S1, get the sending signal The vector sum of received signals on N paths through a fading channel The sending signal is a normalized N-point sampling complex signal, that is, N is an integer power of 2. The received signal is the sum of the time-domain cumulative signals of N paths (the transmitted signal is transmitted to the space according to the direction of the antenna, and the propagation mode includes direct radiation, scattering, and reflection, causing the receiver to receive multi-path signals from different directions).

Step S2, calculate the cross-correlation value of the local sequence (sent signal) and received signal point by point The autocorrelation value of the received signal in is the conjugate of the transmitted signal x _i , A maximum cross-correlation value R _yx (j) among said cross-correlation values is determined for the conjugate of the received signal y _i . The above point-by-point calculation principle includes: when each terminal sends a signal, the previous control frame is the same sequence generated by the serial number generator inside the terminal, such as the pseudo-random sequence here, the length of which is N=1024 (complex signal) ; Then carry out the DFT-S-OFDM modulation change, and send it after framing with the data frame. When it is sent to space propagation, it will undergo changes such as amplitude attenuation, time delay, and frequency offset, so the received signal is exactly the same as the sent signal. Difference. We first need to detect the signal, the first step is to synchronize, how to synchronize, use the terminal at the receiving end to generate a pseudo-random signal (same as the sending terminal) after DFT-S-OFDM modulation change, the obtained local sequence and the sending The front-end signal of the signal is the same, so it can also be considered as the transmission signal x. Do the correlation operation of length N=1024 between the transmitted signal and the received signal obtained locally; because the length of the received signal is more than the length of the control frame, so first assume that the local pseudo-random sequence (the same as the control frame of the transmitted signal) and The first complex signal of the received signal frame header is aligned. Doing a correlation operation is actually to multiply the complex signals 1024 times, then accumulate them, and finally divide the mean value by 1024. In this way, the calculated is a correlation value (1st). Then align the local pseudo-random sequence with the second complex signal of the frame header, and do the same operation. At this time, the last point of the received signal 1024 long participating in the operation is likely to be the following CP (64 long) , but there is no correlation with the pseudo-random sequence, so the calculated correlation value will be very small (the second). Continue, and then align with the third digit to calculate...do this operation one by one, a total of 1024 times, compare and select the maximum value of the cross-correlation values among the calculated cross-correlation values (1024 in total) as the maximum cross-correlation value R _yx (j), that is, it is assumed that the jth cross-correlation value obtained by calculation is the maximum cross-correlation value.

In step S3, a test statistic is calculated according to the value near the maximum cross-correlation value and the autocorrelation value of the received signal, and the test statistic is used to determine the threshold of correlation timing synchronization, thereby determining the starting point of the communication frame. In one embodiment, the calculation method of the test statistic includes: dividing the sum of the 15 values near the maximum cross-correlation value and the autocorrelation value, and the test statistic is the conjugate of the received signal y _i . The communication frame includes a control frame and a data frame; the structure of the communication frame includes a preamble symbol, a cyclic prefix and a data part. In one embodiment, the preamble symbol adopts a pseudo-random sequence with good cross-correlation and auto-correlation. The length of the preamble symbol may be 1024, 512, 256 and so on.

The invention also provides a communication timing synchronization device, which is applied in the DFT-S-OFDM system. In one embodiment, as shown in FIG. 2 , the communication timing synchronization device 1 includes a correlation signal acquisition unit 11 , a maximum cross-correlation value determination unit 12 and a test statistic calculation unit 13 . in:

The relevant signal acquisition unit 11 is used to acquire the transmission signal The received signal on N paths through the fading channel The sending signal is a normalized N-point sampling complex signal, which has N is an integer power of 2. The received signal is the sum of the time-domain cumulative signals of N paths (the transmitted signal is transmitted to the space according to the direction of the antenna, and the propagation mode includes direct radiation, scattering, and reflection, causing the receiver to receive multi-path signals from different directions).

The maximum cross-correlation value determination unit 12 is connected to the correlation signal acquisition unit 11, and is used to calculate the cross-correlation value of the transmitted and received signals point by point A maximum cross-correlation value R _yx (j) among the cross-correlation values is determined for the conjugate of the transmitted signal _xi .

The test statistic calculation unit 13 is connected to the maximum cross-correlation value determination unit 12, and is used to calculate the test statistic according to the value near the maximum cross-correlation value and the received signal autocorrelation value, and the test statistic is used to determine the correlation timing Synchronization threshold to determine the start point of a communication frame. In one embodiment, the calculation method of the test statistic includes: test statistic is the conjugate of the transmitted signal y _i . The communication frame includes a data frame or a control frame; the structure of the communication frame includes a preamble symbol, a cyclic prefix and a data part; the structure of the control frame includes a preamble symbol and a data part. In one embodiment, the preamble symbol adopts a pseudo-random sequence with good cross-correlation and auto-correlation. The length of the preamble symbol may be 1024, 512, 256 and so on.

In order to compare with the present invention, there is a kind of correlation synchronization statistical algorithm in the prior art, the transmission signal of the transmitter is a normalized N-point sampled complex signal, with After Gaussian white noise AWGN channel and fading channel, the received signal is Thus, given the hypothesis testing problem:

where h is the channel impulse response, and is zero mean and variance N-point Gaussian white noise. This gives the hypothesis test statistic The following formula:

In order to obtain the threshold value of the received signal correlation peak ratio, we draw the CDF (cumulative distribution function, cumulative distribution function) of the cumulative distribution function in the AWGN channel environment according to different SNR (Signal Noise Ratio signal-to-noise ratio, signal-to-noise ratio) scenarios The curve is shown in Figure 3 below, and the SNR signal-to-noise ratio is defined as, without loss of generality here, it is assumed that h=1. However, this hypothesis test statistic has two disadvantages. One is that the Doppler frequency offset caused by high-speed movement will greatly reduce the system’s working point and accurately synchronize the frame header of the signal. The working point refers to: the communication link system can communicate normally The lowest signal-to-noise ratio. In this solution, the receiver is at the lowest signal-to-noise ratio, which can be tolerated under the probability (for example, 10e6 communication times, 100 times cannot be synchronized). As shown in Figure 4 below, adding a Doppler frequency offset of 6KHz, the operating point drops at least 15dB; due to the false alarm at 0db-5db-10dB, the false alarm lines overlap completely; at 5dB, it is basically impossible to distinguish the false alarm Leakage alarm line, so Figure 4 shows the CDF curve at 5db 0db-5db, which is almost 15 dB different from Figure 3, that is, the performance drops by 15 dB. Second, the impulse response function is time-invariant, that is, the impulse response function does not change with time. As can be seen from the figure, for fading channels, the hypothesis test statistic is hardly applicable. In Figure 3 and Figure 4, the horizontal axis x is a dimensionless constant from 0 to 1; the vertical axis is the probability of U<=x. The assumption condition H0 indicates that no signal is sent, and all the receiver receives is noise; the assumption condition H1 indicates that the transmission channel passes through the channel plus Gaussian white noise is the received signal of the receiver. The operating points are set to 0dB, -5dB, -10dB respectively.

In one embodiment, the synchronization header (leading symbol) of the present invention adopts a pseudo-random sequence with superior correlation performance (advantage: good cross-correlation and autocorrelation), the length is 1024 points, and the subcarriers are concentrated through DFT changes Mapping, and then do the IFFT change with a length of 2048. And the data sequence is transmitted after being framed according to the frame format of synchronous preamble (Preamble)+CP+data stream (Data).

Aiming at the problem that the hypothesis test statistic U is almost inapplicable to the fading channel, the hypothesis test statistic is now improved and innovated. When the communication channel is a fading channel, the received signal is a time-domain cumulative signal of N paths (the transmitted signal is transmitted to the space according to the direction of the antenna, and the propagation mode has direct radiation, scattering, and reflection, causing the receiver to receive multi-path signals from different directions). and, (ai: signal attenuation coefficient; xi: sending signal; t: time; τ: delay time; j: imaginary part of complex signal, θ _i : Doppler phase deviation; w _i : Gaussian white noise), each point The value of will change randomly, do the cross-correlation operation, the peak point will no longer be estimated. The simulation also found that the hypothesis test statistic U0/U1 (U0: U when the assumption condition H0; U1: U when the assumption condition H1; the value of U: when the probability of missing alarm P _M is 0, the probability of false alarm P _F and For x when it is small (such as P _F =10e-6), see the CDF diagram, the probability of missing alarm under the H1 condition is 0, and the probability of false alarm is also 0 (that is, the probability of false alarm equivalent to the condition of H0 is 1) x Missing alarm probability: refers to the probability that the received signal contains sent information, but is filtered out by a high threshold. False alarm probability: refers to the received signal that does not contain sent information, but is higher than the threshold and is misjudged as The probability of sending valid information) will no longer converge to a certain value, thus concluding that the statistic is no longer applicable to the case of multipath. If the peak value of the main path in the cross-correlation value of the received signal and the local code is taken out, assuming a problem and then making statistics, the threshold value is naturally desirable. However, it is difficult to obtain the peak value of the main path in practical applications. Therefore, considering the CP protection in front of the data segment, the maximum peak value of the cross-correlation value ( The position of the peak point is set to max_index)(Xi*: the conjugate of the transmitted signal Xi. Peak determination: compare the size of the N cross-correlation values R _yx , take the largest value, and directly call the library function max( in the simulation tool matlab ) is enough.) The 15 nearby sample points are accumulated and processed to improve the U value under low SNR, and the following formula is obtained:

Here j=max_index.

In order to verify the performance of the invented hypothesis test statistic, the tool Matlab is used to simulate in fading channel and different signal-to-noise ratio scenarios. The simulation parameter settings are shown in the table below:

Using the Jakes channel model, 4 paths are customized. The delays are 0, 0.2*e-6, 0.4*e-6, and 0.6*e-6, and the unit is second; the path energy losses are 0dB, -2dB, -10dB and -20dB; Doppler frequency offset is -6KHz. The graphics of the simulation results are shown in Figure 5.

By comparing Fig. 4 with Fig. 5, it can be seen that adopting the technical solution of the present invention can solve the threshold problem of the fading channel, so as to obtain a harsh environment with a low signal-to-noise ratio (-10dB) and a Doppler frequency shift as high as 6000 Hz Under the timing synchronization hypothesis test statistic U. In this way, the communication receiver of DFT-S-OFDM utilizes the preamble symbol (the preamble symbol adopts the pseudo-random sequence with relatively good correlation, and the pseudo-random sequence is a definite sequence with certain random characteristics, which are generated by shift registers and have Good cross-correlation, good autocorrelation again. The numerator of U in the present invention has done cross-correlation operation, and denominator has done autocorrelation operation.) Statistical correlation characteristic, carries out serial sliding correlation (because receiver The local pseudo-random sequence of the transmitter is the same as the pseudo-random sequence of the transmitter, and the length is 1024; to find out the frame header of the leading symbol sent, the receiver performs the correlation calculation by sliding the local sequence serially and point by point with the receiver Signal correlation) operation, compare the calculated 1024 values with the threshold value U, if the value exceeds the threshold value U, it can be judged as the starting point of the leading symbol and achieve the synchronization goal. Then remove the length of the preamble symbol and the length of the cyclic prefix CP according to the frame structure, extract effective information for decoding, and obtain accurate transmission information.

In summary, a communication timing synchronization method and device of the present invention has the following beneficial effects: the value of the test statistic in DFT-S-OFDM timing synchronization in a fading channel can be determined, and then determined according to the test statistic The starting point of the communication frame, realizing the timing synchronization of the data frame can determine the threshold value of the test statistic of the timing synchronization of the DFT-S-OFDM communication system in the fading channel, and then determine the starting point of the communication frame according to the threshold value, and realize the timing synchronization of the data frame Timed synchronization. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial application value.

The above-mentioned embodiments only illustrate the principles and effects of the present invention, but are not intended to limit the present invention. Anyone skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical ideas disclosed in the present invention should still be covered by the claims of the present invention.

Claims (10)

1. a kind of communication timing synchronization method, is applied in DFT-S-OFDM systems, it is characterised in that the communication timing synchronization side Method includes：

Obtain sending signalReception signal phasor on Jing fading channel N bars footpath andThe sending signal is normalized N point samplings complex signal, that is, haveN For 2 whole power；

Node-by-node algorithm sending signal and the cross correlation value for receiving signalReceive the autocorrelation value of signalWhereinFor sending signal x_iConjugation,For receiving signal y_iConjugation, determine it is described mutually Maximum cross-correlation value R in the value of pass_yx(j)；

Statistic of test, the inspection are calculated with the autocorrelation value for receiving signal according to the value near the maximum cross-correlation value Statistic is tested for determining the threshold value of related Timing Synchronization, so that it is determined that the starting point of communication frame.

2. communication timing synchronization method according to claim 1, it is characterised in that：The computational methods of the statistic of test include： According to the cumulative of neighbouring 15 values of the maximum cross-correlation value and division operation, statistic of test is done with autocorrelation value $U\left(\stackrel{\&RightArrow;}{y}\right)=\frac{{\left|\frac{1}{N}\underset{i=j-8}{\overset{j+7}{\&Sigma;}}{R}_{yx}\left(i\right)\right|}^2}{\left|\frac{1}{N}\underset{i=1}{\overset{N}{\&Sigma;}}{y}_i{y}_i^{*}\right|},$ For receiving signal y_iConjugation.

3. communication timing synchronization method according to claim 1, it is characterised in that：The communication frame includes control frame and Frame； The structure of the communication frame includes leading symbol, Cyclic Prefix and data division.

4. communication timing synchronization method according to claim 3, it is characterised in that：The leading symbol is superior using correlated performance Pseudo-random sequence.

5. communication timing synchronization method according to claim 3, it is characterised in that：The length of the leading symbol is 1024.

6. a kind of communication timing synchronization device, is applied in DFT-S-OFDM systems, it is characterised in that：The communication timing synchronization dress Put including：

Coherent signal acquiring unit, for obtaining sending signalOn Jing fading channel N bars footpath Receive signalThe sending signal is normalized N point samplings complex signal, is had $\frac{1}{N}\underset{i=1}{\overset{N}{\&Sigma;}}|x_i{|}^2=1,$ N is 2 whole power；

Maximum cross-correlation value determining unit, for node-by-node algorithm sending signal and the cross correlation value for receiving signal For sending signal x_iConjugation, determine maximum cross-correlation value R in the cross correlation value_yx(j)；

Statistic of test computing unit, for calculating with signal autocorrelation value is received according to the value near the maximum cross-correlation value Statistic of test is obtained, the statistic of test is used for determining the threshold value of related Timing Synchronization, so that it is determined that the starting of communication frame Point.

7. communication timing synchronization device according to claim 6, it is characterised in that：Included according to described computational methods：According to The maximum cross-correlation value nearby 15 values cumulative and with receive signal autocorrelation valueDo division operation, Statistic of test For receiving signal y_iConjugation.

8. communication timing synchronization device according to claim 6, it is characterised in that：The communication frame includes control frame and Frame； The structure of the communication frame includes leading symbol, Cyclic Prefix and data division.

9. communication timing synchronization device according to claim 8, it is characterised in that：The leading symbol is superior using correlated performance Pseudo-random sequence.

10. communication timing synchronization device according to claim 8, it is characterised in that：The length of the leading symbol is 1024.