A Synchronization Method and System for OTFS Signals

Abstract

The present invention discloses a synchronization method and system for OTFS signals. The synchronization method includes: S1 obtaining a synchronization sequence according to the frame structure of the OTFS waveform, and using the synchronization sequence with a length of L as the synchronization signal at the transmitting end and the matching signal at the receiving end; S2 performing correlation processing on the received signal and the synchronization sequence to obtain a correlation sequence, and obtaining a synchronization point through the correlation sequence; S3 obtaining the starting point of the received signal according to the synchronization point to achieve timing synchronization at the receiving end; S4 obtaining a frequency deviation according to the timing synchronization result, and achieving carrier synchronization according to the frequency deviation. The present invention shortens the length of the local synchronization sequence, thereby reducing the amount of computation for correlation calculation; performing delay multiplication on the correlated result, with low data storage and few multiplier consumptions; using multiple groups of adjacent synchronization sequences to calculate the frequency deviation, improving the performance of frequency deviation estimation.

Description

Technical Field

[0001] The present invention belongs to the field of electric communication technology, and more specifically, relates to a synchronization method and system for OTFS (Orthogonal Time Frequency Space) signals. Background Art

[0002] In a communication system, the receiving end usually needs to obtain accurate synchronization information of the signal, which is specifically divided into timing synchronization information and carrier synchronization information. Among them, the timing synchronization information is the accurate starting moment of the received signal, and the carrier synchronization information is the frequency deviation between the received signal and the transmitted signal. By using a long known synchronization sequence and performing a correlation operation with a known matching waveform at the receiving end, a better synchronization result can be obtained under low signal-to-noise ratio conditions. However, the longer the synchronization sequence, the higher the computational complexity, and excellent synchronization effects usually come at the cost of more computing resources. Summary of the Invention

[0003] Aiming at the defects of the prior art, the purpose of the present invention is to provide a synchronization method for OTFS signals, aiming to solve the problems of relatively complex existing synchronization operations and a large amount of computing resources.

[0004] The present invention provides a synchronization method for OTFS signals, including the following steps:

[0005] S1 Obtain a synchronization sequence according to the frame structure of the OTFS waveform, and use the synchronization sequence with a length of L as the synchronization signal at the transmitting end and the matching signal at the receiving end;

[0006] S2 Perform correlation processing on the received signal and the synchronization sequence to obtain a correlation sequence, and obtain a synchronization point through the correlation sequence;

[0007] S3 Obtain the starting point of the received signal according to the synchronization point to achieve timing synchronization at the receiving end;

[0008] S4 Obtain the frequency deviation according to the timing synchronization result, and achieve carrier synchronization according to the frequency deviation.

[0009] Wherein, the sampling rate and the number of FFT points of the synchronization sequence are both consistent with the OTFS waveform.

[0010] Furthermore, step S2 is specifically:

[0011] Perform a correlation operation on the received signal and the synchronization sequence, and obtain a first correlation sequence C by dividing the correlation value by the energy value of the received signal;

[0012] Shift the first correlation sequence C by 4L and multiply it by itself to obtain a second correlation sequence C1;

[0013] Shift the second correlation sequence C1 by 2L and multiply it by itself to obtain a third correlation sequence C2;

[0014] Shift the third correlation sequence C2 by 4L and multiply it by itself to obtain a fourth correlation sequence C3;

[0015] There is a maximum peak in the fourth correlation sequence C3, and the position corresponding to this peak is the synchronization point.

[0016] Further preferably, the received signal can be autocorrelated with a step size of L according to the following formula:

[0017]

[0018] where k represents the sampling point number, L represents the synchronization sequence length, j represents the imaginary part, T is the transmission data period, Δf is the frequency deviation, θ is the phase deviation, and n k is Gaussian white noise with a mean of zero and a variance of σ 2 and x(k) is the transmitted data, y(k)=x(k)e j(2πΔfkT+θ) +n k is the received signal; when the training sequence structure is x(k)=x(k + L), then:

[0019] Further preferably, randomly select two adjacent groups of synchronization sequences to perform conjugate multiplication to obtain seven groups of conjugate multiplication values, and calculate the phase and take the average to obtain the frequency deviation.

[0020] where the estimated value of the frequency deviation is obtained according to the following formula

[0021]

[0022] The present invention also provides a synchronization system for OTFS signals, including a timing synchronization module and a carrier synchronization module; the timing synchronization module is used to perform correlation processing on the received signal and the synchronization sequence to obtain the starting point of the received signal and achieve timing synchronization at the receiving end; the carrier synchronization module is used to obtain the frequency deviation according to the timing synchronization result and achieve carrier synchronization according to the frequency deviation.

[0023] Furthermore, the timing synchronization module includes: a synchronization sequence acquisition unit, a correlation processing unit, and a synchronization unit; the synchronization sequence acquisition unit is used to obtain the synchronization sequence according to the frame structure of the OTFS waveform and use the synchronization sequence with a length of L as the synchronization signal at the transmitting end and the matching signal at the receiving end; the correlation processing unit is used to perform correlation processing on the received signal and the synchronization sequence to obtain a correlation sequence and obtain the synchronization point through the correlation sequence; the synchronization unit is used to obtain the starting point of the received signal according to the synchronization point and achieve timing synchronization at the receiving end.

[0024] Among them, the sampling rate and the number of FFT points of the synchronization sequence are both consistent with the OTFS waveform.

[0025] Further preferably, the carrier synchronization module obtains an estimated value of the frequency deviation according to the following formula

[0026]

[0027] Through the above technical solutions conceived by the present invention, compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) In traditional synchronization, usually the complete transmitted sequence is correlated with the received sequence. The transmitted sequence in the present invention is composed of 8 identical synchronization sequences, which shortens the length of the synchronization sequence that needs to perform correlation operations (the length that needs to do correlation is 1 / 8 of the complete transmission length), thereby reducing the amount of computation of the correlation calculation.

[0029] (2) The present invention performs delay multiplication on the correlated result, which only requires 3 multipliers and 7*L storage units, with low data storage and few multipliers consumed.

[0030] (3) The present invention uses multiple groups of adjacent synchronization sequences to calculate the frequency deviation. 8 synchronization sequences can calculate 7 groups of frequency deviation values. After averaging the 7 groups of frequency deviation values, the final frequency deviation estimated value can be obtained, which improves the performance of the frequency deviation estimation compared to the traditional frequency deviation estimation algorithm that only performs one calculation. Description of the Drawings

[0031] Figure 1 It is a schematic flowchart of the implementation process of the OTFS signal synchronization method provided by the embodiment of the present invention;

[0032] Figure 2 It is a schematic diagram of timing synchronization calculation in the OTFS signal synchronization method provided by the embodiment of the present invention;

[0033] Figure 3 It is a schematic diagram of carrier synchronization calculation in the OTFS signal synchronization method provided by the embodiment of the present invention;

[0034] Figure 4 It is a flowchart of the FPGA implementation of timing synchronization calculation provided by the embodiment of the present invention;

[0035] Figure 5 It is a flowchart of the FPGA implementation of carrier synchronization calculation provided by the embodiment of the present invention. Detailed Embodiment

[0036] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] The present invention relates to a method applicable to OTFS signals for synchronizing received signals by constructing a synchronization header using 8 groups of synchronization sequences, which can solve the problems of relatively complex existing synchronization operations and large computational resources.

[0038] The present invention designs a group of local synchronization sequences, and the generation method of the sequences is similar to the designed OTFS signals, so as to ensure the consistency between the synchronization segment and the waveform segment. After repeating the synchronization sequence 8 times and adding CP, the synchronization header to be sent is formed. As Figure 1 shown, the receiving end correlates the local synchronization sequence with the received signal. Since the local synchronization sequence is actually only about 1 / 8 of the length of the synchronization signal, the computational complexity of the correlation operation can be greatly reduced. Then, after adding the correlation values with multiple delays, the timing synchronization peak value is obtained, thereby realizing timing synchronization. After successful timing synchronization, according to the timing synchronization peak value, conjugate multiplication is performed on two adjacent groups of received synchronization sequences, a total of 7 groups of conjugate multiplication values are obtained, and the mean value is calculated after taking their phases, so that the received frequency deviation can be obtained, thereby performing carrier synchronization.

[0039] Specifically, the synchronization method for OTFS signals provided by the present invention includes the following steps:

[0040] (1) Design a synchronization sequence according to the frame structure of the OTFS waveform. The indexes such as the sampling rate and the number of FFT points of the sequence are the same as those of the OTFS waveform. The synchronization sequence with a length of L is stored locally as the synchronization signal at the transmitting end and the matching signal at the receiving end;

[0041] (2) As Figure 2 shown, the receiving end correlates the received signal with the known local synchronization sequence, and calculates the correlation value divided by the energy value of the received signal. This process obtains the first correlation sequence C, which contains 8 peaks; the first correlation sequence C is shifted by 4L and multiplied by itself to obtain the second correlation sequence C1, which contains 4 peaks; then C1 is shifted by 2L and multiplied by itself to obtain the third correlation sequence C2, which contains 2 peaks; finally, C2 is shifted by 4L and multiplied by itself to obtain the fourth correlation sequence C3. There will be a maximum peak in C3, and the position corresponding to this peak is the synchronization point.

[0042] (3) After the timing synchronization is completed, according to the timing synchronization peak value, the starting point of the received signal can be known. Assuming that the ideal transmitted data is x(k), the data received by the receiver is y(k), and the received signal can be expressed as y(k) = x(k)e j(2 πΔfkT+θ) +n k, where T is the transmission data period, Δf is the frequency deviation, θ is the phase deviation, and n k is Gaussian white noise with a mean of zero and a variance of σ 2 . The autocorrelation of the received signal is performed with a step size of L. Without considering noise, the correlation operation is performed as follows:

[0043]

[0044] where the training sequence structure is x(k) = x(k + L), then:

[0045] Taking the phase of the above equation can obtain the estimated value of the frequency deviation:

[0046]

[0047] As Figure 3 shown, select the conjugate multiplication of two adjacent groups of received synchronization sequences, a total of 7 groups of conjugate multiplication values are obtained, and the mean value is calculated after taking the phase, then the received frequency deviation can be obtained, and thus carrier synchronization can be performed.

[0048] The following is a further description of the present invention based on an embodiment of FPGA processing, but this embodiment should not be construed as a limitation of the present invention; the details are described as follows with reference to the accompanying drawings:

[0049] As Figure 1 shown, the synchronization system of the OTFS signal includes a timing synchronization module and a carrier synchronization module. Among them, the carrier synchronization module needs to use the calculation result of the timing synchronization module.

[0050] The timing synchronization module completes the timing synchronization function at the receiving end by correlating the received signal with the local waveform, that is, finding the accurate starting time of the received signal;

[0051] The carrier synchronization module selects the conjugate multiplication of two adjacent groups of received synchronization sequences according to the timing synchronization result, a total of 7 groups of conjugate multiplication values are obtained, the mean value is taken after calculating the phase, and the received frequency deviation can be obtained, and thus carrier synchronization can be performed.

[0052] As Figure 4As shown in the figure, the working process of the timing synchronization module is as follows: After the received signal is subjected to sliding window multiplication and accumulation with the local correlation sequence (i.e., correlation operation), it is divided by the current signal energy to obtain the first correlation sequence C. This process can be completed using the filter IP core in the FPGA, with relatively low resource consumption; then the first correlation sequence C is delayed by 4L and multiplied by itself to obtain the second correlation sequence C1. This process consumes 4L length registers and 1 multiplier; then C1 is delayed by 2L and multiplied by itself to obtain the third correlation sequence C2. This process consumes 2L length registers and 1 multiplier; finally, C2 is delayed by L and multiplied by itself to obtain the fourth correlation sequence C3. This process consumes L length registers and 1 multiplier. There will be a maximum peak in C3, and the position corresponding to this peak is the synchronization point.

[0053] The working process of the carrier synchronization module is as follows: After timing synchronization is completed, the starting position of the received signal is known, that is, the corresponding positions of the 8-segment synchronization sequence are known. After the received signal is delayed by L points, the conjugate multiplication and accumulation of the synchronization sequence N and the synchronization sequence N + 1 are completed (N = 1 to 7), and a total of 7 groups of correlation values of adjacent synchronization sequences are obtained. This process consumes L length registers and 1 multiplier; then the phases of the above 7 groups of correlation values are calculated, and the average value Φ of the 7 groups of phases is obtained. This process can be completed using the IP core in the FPGA; finally, according to the phase Φ, the frequency deviation Δf is calculated.

[0054] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A synchronization method for OTFS signals, characterized in that, it includes the following steps: S1 Obtain a synchronization sequence according to the frame structure of the OTFS waveform, and use the synchronization sequence with length L as the synchronization signal at the transmitting end and the matching signal at the receiving end; S2 Perform correlation processing on the received signal and the synchronization sequence to obtain a correlation sequence, and obtain a synchronization point through the correlation sequence; S3 Obtain the starting point of the received signal according to the synchronization point to achieve timing synchronization at the receiving end; S4 Obtain the frequency deviation according to the timing synchronization result, and achieve carrier synchronization according to the frequency deviation; Step S2 is specifically: Perform correlation operation on the received signal and the synchronization sequence, and obtain the first correlation sequence C by dividing the correlation value by the energy value of the received signal; Multiply the first correlation sequence C by itself after shifting it by 4L to obtain the second correlation sequence C1; Multiply the second correlation sequence C1 by itself after shifting it by 2L to obtain the third correlation sequence C2; Multiply the third correlation sequence C2 by itself after shifting it by L to obtain the fourth correlation sequence C3; There is a maximum peak in the fourth correlation sequence C3, and the position corresponding to this peak is the synchronization point; Repeat the synchronization sequence 8 times and add CP to form the synchronization header to be sent.

2. The synchronization method according to claim 1, characterized in that, the sampling rate and the number of FFT points of the synchronization sequence are both consistent with the OTFS waveform.

3. The synchronization method according to claim 1, characterized in that, Perform autocorrelation operation on the received signal with a step size of L according to the following formula: Among them, k represents the sampling point serial number, L represents the synchronization sequence length, j represents the imaginary part, T is the transmission data period, Δf is the frequency deviation, θ is the phase deviation, and n k is Gaussian white noise with a mean of zero and a variance of σ 2 and x(k) is the transmitted data, y(k) = x(k)e j(2 πΔfkT+θ) +n k is the received signal; when the training sequence structure is x(k) = x(k + L), then:

4. The synchronization method according to claim 1, characterized in that, Arbitrarily select two adjacent groups of synchronization sequences to perform conjugate multiplication to obtain seven groups of conjugate multiplication values, and calculate the phase and take the average value respectively to obtain the frequency deviation.

5. The synchronization method according to claim 4, characterized in that, An estimated value of the frequency deviation is obtained according to the following formula f s = 1 / T, where L represents the length of the synchronization sequence and T is the transmission data period.

6. An OTFS signal synchronization system, characterized in that, it includes a timing synchronization module and a carrier synchronization module; The timing synchronization module is used to perform correlation processing on the received signal and the synchronization sequence, obtain the starting point of the received signal, and achieve timing synchronization at the receiving end; The carrier synchronization module is used to obtain the frequency deviation according to the timing synchronization result, and achieve carrier synchronization according to the frequency deviation; The timing synchronization module includes: a synchronization sequence acquisition unit, a correlation processing unit and a synchronization unit; The synchronization sequence acquisition unit is used to obtain a synchronization sequence according to the frame structure of the OTFS waveform, and use the synchronization sequence with length L as the synchronization signal at the transmitting end and the matching signal at the receiving end; The correlation processing unit is used to perform correlation processing on the received signal and the synchronization sequence to obtain a correlation sequence, and obtain a synchronization point through the correlation sequence; The synchronization unit is used to obtain the starting point of the received signal according to the synchronization point to achieve timing synchronization at the receiving end; Repeat the synchronization sequence 8 times and add CP to form the synchronization header to be sent; Specifically, the correlation processing unit performs the following steps: Perform correlation operation on the received signal and the synchronization sequence, and obtain the first correlation sequence C by dividing the correlation value by the energy value of the received signal; Shift the first correlation sequence C by 4L and multiply it by itself to obtain a second correlation sequence C1; Shift the second correlation sequence C1 by 2L and multiply it by itself to obtain a third correlation sequence C2; Shift the third correlation sequence C2 by L and multiply it by itself to obtain a fourth correlation sequence C3; There is a maximum peak in the fourth correlation sequence C3, and the position corresponding to this peak is the synchronization point.

7. The synchronization system according to claim 6, wherein, the sampling rate and the number of FFT points of the synchronization sequence are both consistent with the OTFS waveform.

8. The synchronization system according to claim 7, wherein, The carrier synchronization module obtains an estimated value of the frequency deviation according to the following formula f s = 1 / T, where L represents the length of the synchronization sequence and T is the transmission data period.

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