An improved method of timing synchronization for initial phase injection

Abstract

The application provides an improved timing synchronization method for initial phase injection, comprising the following steps: S1, performing square filtering on an input signal to estimate timing error and obtaining a square filtering timing error value; S2, taking the square filtering timing error value as an initial position of an interpolation point of a Gardner timing loop, and performing Gardner timing error estimation on optimal sampling data obtained after interpolation; S3, inputting the timing error value into a loop filter, a gain control filter and a selection controller, adjusting a loop coefficient through the selection controller, multiplying a sum of outputs of the loop filter and the gain control filter by the loop coefficient to obtain a control word of a numerically controlled oscillator; S4, the numerically controlled oscillator generates an update value of a fractional interval through overflow counting to change a position of an interpolation base point, and forms a closed-loop feedback timing synchronization loop, and the interpolation base point is iteratively adjusted to obtain optimal sampling data; and S5, performing downsampling filtering on the optimal sampling data to output optimal sampling data.

Description

Technical Field

[0001] This application relates to the field of communication technology, and more specifically, to an improved timing synchronization method for initial phase injection. Background Technology

[0002] In communication systems, signals are affected by the Doppler effect during channel transmission. Furthermore, clock mismatches between the transmitter and receiver can occur, resulting in frequency and phase offsets between the received and transmitted signals. When frequency or phase offsets exist, the sampling clock cannot sample the signal at the optimal sampling time, leading to deviations between the sampled values ​​and the ideal values. This deviation affects subsequent symbol decision-making during demodulation, degrading signal quality and increasing the bit error rate during decoding. Therefore, bit synchronization is necessary to compensate for and correct the frequency and phase offsets of the sampling clock.

[0003] The earliest bit synchronization method was the pilot insertion method, which requires inserting a pilot signal into the data frame. The receiver then uses this pilot signal for bit synchronization. Pilot signals consume a significant amount of transmission energy, increase spectrum resources, and affect signal throughput, thus they are rarely used in practical communication systems.

[0004] Currently, commonly used bit synchronization methods mainly include the square-filter timing estimation algorithm and the Gardner timing error estimation algorithm. The square-filter timing estimation algorithm is a feedforward structure estimation algorithm. This method first performs a square nonlinear transformation on the received signal, and then extracts the frequency component at 1 / T through digital filtering, thereby obtaining an estimate of the timing error. The square-filter timing estimation algorithm has a fast convergence speed, but it requires a high sampling rate from the ADC, at least four times oversampling, and its tracking performance is poor, unable to withstand large timing errors. The Gardner timing error estimation algorithm is a feedback structure estimation algorithm. This algorithm only requires two sampling points to calculate the timing error value for each symbol. The Gardner timing error estimation algorithm is widely used because of its simple bit synchronization loop structure and the advantage that its synchronization performance is not affected by carrier phase interference, but its convergence speed is slow and it is not suitable for burst transmissions. Summary of the Invention

[0005] This invention provides an improved timing synchronization method for initial phase injection, the timing synchronization method for initial phase injection comprising the following steps:

[0006] S1: Perform square filtering on the input signal to estimate the timing error, obtain the square filtering timing error value, and complete the clock initial phase capture;

[0007] S2: Use the above squared filter timing error value as the initial position of the Gardner timing loop interpolation point, and perform Gardner timing error estimation on the best sampled data obtained after interpolation.

[0008] S3: Input the Gardner timing error value calculated above into the loop filter, gain control filter and selection controller simultaneously. Adjust the loop coefficient through the selection controller. Multiply the sum of the outputs of the loop filter and gain control filter by the loop coefficient to obtain the control word of the numerically controlled oscillator.

[0009] S4: The numerically controlled oscillator generates an update value at fractional intervals by overflow counting, changes the position of the interpolation base point, forms a closed-loop feedback timing synchronization loop, and then performs cyclic iteration to continuously adjust the interpolation base point to obtain the best sampling data;

[0010] S5: Perform downsampling filtering on the above optimal sampled data and output the optimal sampled data after downsampling filtering.

[0011] Furthermore, step 1 also includes the following steps:

[0012] S11: Initialize the control word of the first numerically controlled oscillator and acquire input data simultaneously;

[0013] S12: Input data is fed into the interpolation filter and output under the control of the first numerically controlled oscillator. When the number of output data reaches the predetermined value, the initial phase of the clock is estimated.

[0014] S13: The initial phase estimate of the clock is calculated by the square filtering algorithm, and the initial phase estimate of the clock is used to complete the initialization of the second numerically controlled oscillator.

[0015] Furthermore, in step S13, the square filtering algorithm first performs a square nonlinear transformation on the received signal, and then extracts the frequency component at 1 / T through digital filtering, thereby obtaining an estimate of the timing deviation. The calculation formula is:

[0016]

[0017] Where r(k) represents the data output by the interpolation filter under the control of the first numerically controlled oscillator, k represents the sampling point, N represents the number of sampling points in one symbol period, L represents the symbol length, usually L is 64 to meet the requirements, and arg represents the angle taking operation.

[0018] When the number of output data reaches LN, the initial phase of the clock is estimated.

[0019] Furthermore, step S2 also includes the following steps:

[0020] S21: The input data is processed by the interpolation filter under the control of the second numerically controlled oscillator to obtain the interpolation sequence of the loop;

[0021] S22: Perform timing error estimation on the interpolation sequence according to the Gardner algorithm to obtain the timing error signal.

[0022] Furthermore, step S3 also includes the following steps:

[0023] S31: Input the timing error into the loop filter to filter out the high-frequency components, and at the same time input the timing error into the gain control filter;

[0024] S32: The selector determines the loop state by calculating the mean value of the timing error, and then adjusts the loop coefficient.

[0025] S33: The sum of the outputs of the loop filter and the gain control filter, multiplied by the loop coefficient, is used as the control word for the second numerically controlled oscillator.

[0026] Furthermore, step S4 also includes the following steps:

[0027] S41: The second numerically controlled oscillator determines the interpolation base point and fractional interval required by the interpolation filter by overflow counting;

[0028] S42: The interpolation filter uses the interpolation base point and fractional interval to complete a new round of interpolation calculation, thus forming a closed-loop feedback loop. Through iterative iteration, the position of the interpolation base point is continuously adjusted to obtain the optimal sampling data.

[0029] The beneficial effects of this application are:

[0030] This invention combines the advantages of the squared-filter timing estimation algorithm and the Gardner timing error estimation algorithm, using the squared-filter timing error value as the initial position of the Gardner algorithm interpolation point, thereby enabling the Gardner timing recovery loop to lock quickly and shortening the timing synchronization establishment time.

[0031] This invention adds a gain control filter, a selection controller, and loop coefficients to the traditional Gardner timing recovery loop. The sum of the outputs of the loop filter and the gain control filter, multiplied by the loop coefficients, is used as the control word for the numerically controlled oscillator. The selection controller is used to determine the loop state and adjust the loop coefficients accordingly. The improved loop structure can effectively reduce timing jitter errors caused by system self-noise during synchronization. Attached Figure Description

[0032] The advantages of the above and / or additional aspects of this application will become apparent and readily understood in the description of the embodiments in conjunction with the following drawings, wherein:

[0033] Figure 1 This is a flowchart of an improved timing synchronization method for initial phase injection provided by an embodiment of the present invention;

[0034] Figure 2 This is a schematic diagram of an improved timing synchronization device for initial phase injection provided in an embodiment of the present invention;

[0035] Figure 3 This is a diagram illustrating the update process of the NCO register phase value in an improved timing synchronization method for initial phase injection provided by an embodiment of the present invention.

[0036] Figure 4 This is a schematic diagram of the squared-filter timing error estimation algorithm in an improved initial phase injection timing synchronization method provided by an embodiment of the present invention.

[0037] Figure 5 This is a schematic diagram of the Gardner timing error detection algorithm in an improved initial phase injection timing synchronization method provided in an embodiment of the present invention.

[0038] Figure 6 This is a schematic diagram illustrating the working principle of the gain control filter in an improved initial phase injection timing synchronization method provided by an embodiment of the present invention.

[0039] Figure 7 This is a schematic diagram illustrating the working principle of the controller selected in an improved timing synchronization method for initial phase injection provided by an embodiment of the present invention.

[0040] Figure 8 This is a block diagram of the cubic interpolation filter in an improved initial phase injection timing synchronization method provided by an embodiment of the present invention. Detailed Implementation

[0041] To better understand the above-mentioned objectives, features, and advantages of this application, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of this application can be combined with each other.

[0042] In the following description, many specific details are set forth in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of this application is not limited to the specific embodiments disclosed below.

[0043] As attached Figure 1 As shown, an improved timing synchronization method for initial phase injection includes the following steps:

[0044] S1: Perform square filtering on the input signal to estimate the timing error, obtain the square filtering timing error value, and complete the clock initial phase capture;

[0045] Specifically, step S1 also includes:

[0046] S11: Initialize the first numerically controlled oscillator NCO1, thereby initializing the initial value of the NCO1 register, initializing the control word, and simultaneously sending the input data into data buffer 1;

[0047] S12: Close the switch to k1, retrieve data from data buffer 1 and enter interpolation filter 1. Under the control of the first numerically controlled oscillator NCO1, continuously store the data output by interpolation filter 1 into data buffer 2. When the number of stored data reaches LN, the initial phase of the clock can be estimated.

[0048] S13: The estimated initial phase of the clock is obtained by calculating the square filter algorithm. And complete the initialization of the numerically controlled oscillator NCO2.

[0049] Specifically, both the first numerically controlled oscillator NCO1 and the numerically controlled oscillator NCO2 are phase decrementers, which determine the interpolation base point m by overflow counting under the action of the step size control word ω(m). k In this system, the step size control word of the first numerically controlled oscillator NCO1 is a predetermined constant; the step size control word ω(m) of the numerically controlled oscillator NCO2 is provided by the loop filter. The function of the phase decrementer can be expressed by the formula:

[0050]

[0051] η(m) represents the value of the NCO register when the m-th sampling time arrives, η(m+1) represents the value of the NCO register when the (m+1)-th sampling time arrives, and mod1 represents the modulo 1 operation.

[0052] Appendix Figure 3 The update process of the phase values ​​of the NCO1 and NCO2 registers is intuitively shown, from which the following can be derived using the similar triangle rule:

[0053]

[0054] Where, μ k Denotes the fractional interval, m k T represents the interpolation base point. s This indicates the sampling clock period.

[0055] After shifting and deforming it, the fractional interval μ can be obtained. k The expression:

[0056]

[0057] Where, ω(m) k ) represents the step size control word of the loop filter output.

[0058] In this embodiment, since the input data is 4 times oversampled data, the control word ω of the numerically controlled oscillator NCO1 is... NCO1 (m) is set to a constant 1, and the initial value η of the NCO1 register is... NCO (1) Set to 1.

[0059] Specifically, the squared filtering algorithm in step S13 is as follows: Figure 4 As shown, this method first performs a squared nonlinear transformation on the received signal, and then extracts the frequency component at 1 / T through digital filtering, thereby obtaining an estimate of the timing deviation. The calculation formula is:

[0060]

[0061] Where r(k) represents the data output by the interpolation filter under the control of the first numerically controlled oscillator, k represents the sampling point, N represents the number of sampling points in one symbol period, L represents the symbol length (usually L = 64 is sufficient), and arg represents the angle taking operation. In this embodiment, the timing deviation estimate is calculated using the first 256 input symbols. That is, N is 4 and L is 64.

[0062] Obtain the estimated timing deviation value Then the numerically controlled oscillator NCO2 can be initialized, which is similar to that of NCO1, but for NCO2, the control word ω NC (m) is not a constant; its overflow period changes dynamically. Since N is 4, the initial value ω of the NCO2 control word is set. NCO2 (1) is 0.5, the initial value η of the NCO2 register NC (1) is After completing the initialization settings for NCO2, proceed to step S2.

[0063] S2: Use the above squared filter timing error value as the initial position of the Gardner timing loop interpolation point, and perform Gardner timing error estimation on the best sampled data obtained after interpolation.

[0064] Specifically, step S2 also includes:

[0065] S21: Close the switch to k2, and calculate the interpolation sequence of the loop by passing the data in the data buffer 1 through the interpolation filter 2 under the control of the numerically controlled oscillator NCO2;

[0066] S22: The timing error detector performs timing error estimation on the interpolation sequence according to the Gardner algorithm to obtain the timing error signal e(n).

[0067] Specifically, in step S22, the Gardner algorithm is used to estimate the timing error. The expression for the traditional Gardner timing error detection algorithm is as follows:

[0068]

[0069] Where e(n) is the calculated timing error value, y I (n), y Q (n) represents the symbol sampled value of the nth in-phase signal and the quadrature signal, respectively. I (n-1), y Q (n-1) represent the symbol sample values ​​of the (n-1)th in-phase signal and the quadrature signal, respectively. These represent the intermediate sample values ​​at the (n-1)th and nth sampling times of the in-phase and quadrature signals, respectively. (See attached image.) Figure 5 As shown in the diagram, in a), the intermediate sample value is zero, and the timing error output value is zero, which is the optimal sampling point for the loop; in b), the intermediate sample value is greater than zero, indicating that the sampling clock is ahead and the interpolation needs to be adjusted backward; in c), the intermediate sample value is less than zero, indicating that the sampling clock is behind and the interpolation needs to be adjusted forward.

[0070] S3: Input the Gardner timing error value calculated above into the loop filter, gain control filter and selection controller simultaneously. Adjust the loop coefficient through the selection controller. Multiply the sum of the outputs of the loop filter and gain control filter by the loop coefficient to obtain the control word of the numerically controlled oscillator.

[0071] Specifically, step S3 also includes:

[0072] S31: Input the detected timing error e(n) into the loop filter to filter out the high-frequency components, and at the same time input the timing error e(n) into the gain control filter;

[0073] S32: The selector determines the loop state by calculating the mean error, and then adjusts the loop coefficient accordingly;

[0074] S33: Multiply the sum of the outputs of the loop filter and the gain control filter by the loop coefficient as the control word ω(m) of the numerically controlled oscillator NCO2, and update the value of NCO register 2.

[0075] Furthermore, the loop filter described in step S31 primarily functions to filter out high-frequency interference components in the timing error signal. In this embodiment, a second-order active proportional-integral filter is used to implement the loop filtering function, and the corresponding transfer function expression is: Where coe1 and coe2 are the coefficients of the loop filter, and the specific calculation formula is as follows: ω n Let K represent the loop bandwidth, ξ represent the damping factor, and K represent the loop width. m It is the gain of the NCO, K d It is the phase detection gain of the timing error detector, f s This represents the operating frequency of the loop filter, i.e., the frequency of the local sampling clock at the receiver. The recursive equation for the loop filter is:

[0076] ω(n)=ω(n-1)+coe1·[e(n)-e(n-1)]+coe2·e(n)

[0077] Specifically, the working principle diagram of the gain control filter described in step S31 is attached. Figure 6 As shown, the filter sets an error threshold u. ref By detecting whether the timing error e(n) exceeds a threshold, if the continuous input exceeds a certain number m, the output error value e′(n) = sign(e(n))·(u ref Otherwise, the output error value e′(n) = 0. In this embodiment, after parameter simulation, m is set to 3, u ref The gain control filter performs best when set to 0.2.

[0078] Furthermore, the working principle diagram of the selection controller described in step S32 is attached. Figure 7 As shown, the controller determines the loop state by calculating the average error value. When the average value approaches zero, the timing synchronization loop enters the tracking state; otherwise, it remains in the capture state. When the loop is in the capture state, the loop coefficient is set to 1. In the tracking state, the loop coefficient should be between 0 and 1, requiring simulation experiments to comprehensively analyze timing jitter and synchronization time before finally selecting the appropriate loop coefficient value. In this embodiment, when the loop is in the tracking state, simulation experiments are used to comprehensively analyze timing jitter and synchronization time, ultimately setting the loop coefficient to 0.1.

[0079] S4: The numerically controlled oscillator generates an update value at fractional intervals by overflow counting, changes the position of the interpolation base point, forms a closed-loop feedback timing synchronization loop, and then performs cyclic iteration to continuously adjust the interpolation base point to obtain the best sampling data;

[0080] Specifically, step S4 also includes:

[0081] S41: The numerically controlled oscillator NCO2, under the control of ω(m), determines the interpolation base point m required by the interpolation filter 2 through overflow counting. k and fractional interval μ k ;

[0082] S42: Interpolation filter 2 utilizes m k and μ k A new round of interpolation calculations is completed, thus forming a closed-loop feedback circuit. Through iterative iteration, the position of the interpolation base point is continuously adjusted to obtain the optimal sampling data.

[0083] Specifically, the interpolation filter mentioned in steps S1 and S2 generally adopts a polynomial interpolation filter. Its basic principle is to approximate the interpolation point y(kT) with an Nth-order Lagrange polynomial function. i From the calculation formula, we obtain the expression for the Lagrange interpolation formula:

[0084]

[0085] Where C i (t) represents the Lagrange coefficient, and its specific expression is: Since the number N of interpolator tap coefficients involved in the interpolation point calculation must be even, we can set I1 = -N / 2 and I2 = N / 2 - 1. This is because only the unit impulse response of the interpolation filter needs to be within (μ... k +i)T s The sampled value h at time 1 I [(μ k +i)T s Therefore, let t μ =(μ k +i)T s Then we can obtain the expression for the Lagrange interpolation filter:

[0086] h I [(μ k +i)T s ] = C i (μ k )

[0087] in,

[0088] This example uses a cubic interpolation filter with a Farrow structure, the block diagram of which is attached. Figure 8 As shown, if the interpolation filter order N = 4, then I1 = -2, I2 = 1, and the cubic interpolation coefficients are... The formula for calculating the interpolation point is y(kT) i ) = C-2 (μ k )x(m k +2)+C -1 (μ k )x(m k +1)+C0(μ k )x(m k )+C1(μ k )x(m k -1).

[0089] S5: Perform downsampling filtering on the above optimal sampled data and output the optimal sampled data after downsampling filtering.

[0090] This invention presents an improved timing synchronization method for initial phase injection, employing a combination of a squared-filter timing estimation algorithm and a Gardner timing error estimation algorithm for signal timing synchronization. First, the signal's initial phase is captured through squared-filter error estimation. Then, the squared-filter timing error value is used as the initial position of the Gardner algorithm's interpolation point, enabling the Gardner timing recovery loop to lock quickly and shortening the timing synchronization setup time. Furthermore, a gain control filter, a selection controller, and loop coefficients are added to the traditional Gardner timing recovery loop, effectively reducing timing jitter errors caused by system self-noise during synchronization. Compared to the traditional Gardner timing recovery algorithm, this invention effectively shortens the synchronization setup time and reduces timing jitter errors.

[0091] The steps in this application can be rearranged, combined, or deleted according to actual needs.

[0092] Although this application has been disclosed in detail with reference to the accompanying drawings, it should be understood that these descriptions are merely exemplary and not intended to limit the application of this application. The scope of protection of this application is defined by the appended claims and may include various variations, modifications, and equivalents of the invention without departing from the scope and spirit of this application.

Claims

1. An improved method for timing synchronization of initial phase injection, characterized in that, The timing synchronization method for the initial phase injection includes the following steps: S1: Perform square filtering on the input signal to estimate the timing error, obtain the square filtering timing error value, and complete the clock initial phase capture; S2: Use the above squared filter timing error value as the initial position of the Gardner timing loop interpolation point, and perform Gardner timing error estimation on the best sampled data obtained after interpolation. S3: Input the Gardner timing error value calculated above into the loop filter, gain control filter and selection controller simultaneously. Adjust the loop coefficient through the selection controller. Multiply the sum of the outputs of the loop filter and gain control filter by the loop coefficient to obtain the control word of the numerically controlled oscillator. S4: The numerically controlled oscillator generates an update value at fractional intervals by overflow counting, changes the position of the interpolation base point, forms a closed-loop feedback timing synchronization loop, and then performs cyclic iteration to continuously adjust the interpolation base point to obtain the best sampling data; S5: Perform downsampling filtering on the above optimal sampling data and output the optimal sampling data after downsampling filtering; Step S3 includes the following steps: S31: Input the timing error into the loop filter to filter out the high-frequency components, and at the same time input the timing error into the gain control filter; Setting an error threshold in a gain control filter By measuring timing error The system checks whether the input exceeds a threshold. If the number of consecutive inputs exceeds a certain threshold (m), the system outputs an error value. Otherwise, output error value ; S32: The selector determines the loop state by calculating the mean value of the timing error, and then adjusts the loop coefficient. S33: The sum of the outputs of the loop filter and the gain control filter, multiplied by the loop coefficient, is used as the control word for the second numerically controlled oscillator.

2. The timing synchronization method for initial phase injection according to claim 1, characterized in that, Step 1 also includes the following steps: S11: Initialize the control word of the first numerically controlled oscillator and acquire input data simultaneously; S12: Input data is fed into the interpolation filter and output under the control of the first numerically controlled oscillator. When the number of output data reaches the predetermined value, the initial phase of the clock is estimated. S13: The initial phase estimate of the clock is calculated by the square filtering algorithm, and the initial phase estimate of the clock is used to complete the initialization of the second numerically controlled oscillator.

3. The timing synchronization method for initial phase injection according to claim 2, characterized in that, In step S13, the square filtering algorithm first performs a square nonlinear transformation on the received signal, and then extracts the frequency component at 1 / T through digital filtering, thereby obtaining an estimate of the timing deviation. The calculation formula is: ； in, This represents the data output by the interpolation filter under the control of the first numerically controlled oscillator. Indicates the sampling point. This represents the number of sampling points within one symbol period. The symbol length is indicated; usually, 64 L is sufficient. arg represents the angle operation. When the number of output data reaches LN, the initial phase of the clock is estimated.

4. The timing synchronization method for initial phase injection according to claim 1, characterized in that, Step S2 also includes the following steps: S21: The input data is processed by the interpolation filter under the control of the second numerically controlled oscillator to obtain the interpolation sequence of the loop; S22: Perform timing error estimation on the interpolation sequence according to the Gardner algorithm to obtain the timing error signal.

5. The timing synchronization method for initial phase injection according to claim 1, characterized in that, Step S4 also includes the following steps: S41: The second numerically controlled oscillator determines the interpolation base point and fractional interval required by the interpolation filter by overflow counting; S42: The interpolation filter uses the interpolation base point and fractional interval to complete a new round of interpolation calculation, thus forming a closed-loop feedback loop. Through iterative iteration, the position of the interpolation base point is continuously adjusted to obtain the optimal sampling data.

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