Synchronization point calculation method based on LTE-V2X

Abstract

The invention discloses a synchronization point calculation method based on LTE-V2X, which belongs to the technical field of measurement, and comprises the following steps: receiving an LTE-V2X baseband signal; when the power is triggered and a baseband signal is switched from an idle state to an effective signal, the instantaneous power of the signal is obviously increased. By setting a reasonable power threshold, the jump can be detected so as to obtain a coarse synchronization point. DMRS time domain sequences on four time slots of a PSCCH channel are utilized; intercepting four kinds of reference signals, and calculating a fine synchronization point; and calculating a final synchronization point of the LTE-V2X. According to the method, the accuracy of LTE-V2X synchronization point calculation can be improved, the error of the system is reduced, the initial position of the service channel can be accurately found under the condition of no broadcast channel, and the robustness of the system is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of synchronization point calculation, and in particular relates to a synchronization point calculation method based on LTE-V2X. Background Art

[0002] In LTE-V2X (Vehicle-to-Everything) communications, vehicles exchange low-latency, high-reliability information, such as collision warning and cooperative driving, over a direct link (PC5 interface). Because V2X communications typically operate in high-speed mobile scenarios and lack the precise synchronization support of cellular networks (such as eNBs), receivers must rely on physical layer signals (such as the DMRS of the PSCCH) to autonomously synchronize time and frequency to ensure correct demodulation of subsequent data.

[0003] In traditional LTE cellular communications, the terminal (UE) can quickly complete time and frequency synchronization through the primary synchronization signal (PSS) and the secondary synchronization signal (SSS). However, in LTE-V2X Mode 4 (distributed scheduling):

[0004] 1. No broadcast synchronization signal: Vehicle-to-vehicle communication does not rely on base stations and cannot use PSS / SSS.

[0005] 2. Dynamic topology changes: The high-speed movement of vehicles causes rapid changes in the channel. Traditional correlation-based synchronization methods (such as sliding correlation) are susceptible to Doppler frequency shift and multipath interference.

[0006] To address these issues, the present invention proposes a synchronization method based on multi-symbol DMRS joint verification. First, coarse synchronization is achieved using time-domain correlation. Frequency-domain analysis is then used to precisely locate the first valid signal path, avoiding multipath interference. Finally, the synchronization results from the four symbols are combined, and a majority voting statistical method is used to determine the final synchronization point. This method maintains high accuracy in high-speed mobility scenarios with moderate computational complexity, effectively improving synchronization reliability in V2X communications. Summary of the Invention

[0007] In response to the above-mentioned problems existing in the prior art, the present invention proposes a synchronization point calculation method based on LTE-V2X, which has a reasonable design, solves the shortcomings of the prior art, and has good effects.

[0008] A synchronization point calculation method based on LTE-V2X includes the following steps:

[0009] Step 1: Obtain LTE-V2X baseband signal data;

[0010] Step 2: Calculate the number of RBs and RB offsets for PSCCH and PSSCH channels through blind detection.

[0011] Step 3: Calculate the coarse synchronization point using power triggering;

[0012] Step 4: Calculate the precise synchronization point using the PSCCH 4 DMRS sequences;

[0013] Step 5: Calculate the final synchronization point of LTE-V2X.

[0014] Furthermore, step 3 includes the following sub-steps:

[0015] Step 3.1: Calculate the instantaneous power of the signal, specifically:

[0016] For the received signal Y[n], calculate the instantaneous power P[n] at each sampling point, as shown in formula (1):

[0017] P[n]=|Y[n]| 2 =Real(Y[n]) 2 +Imag(Y[n]) 2 (1)

[0018] Calculate the short-time average power of the signal, specifically:

[0019] The power is smoothed by sliding the window to reduce the influence of noise, as shown in formula (2):

[0020]

[0021] in, is the short-time average power of the signal, L is the length of the rectangular window, P[nk] is the instantaneous power of the nkth sampling point, and n is the sequence number of the current sampling point;

[0022] Step 3.2: Set the empirical threshold, specifically:

[0023] According to the statistical characteristics of noise power and signal power, the threshold T is set as shown in formula (3):

[0024]

[0025] in, is the empirical coefficient, is the noise power;

[0026] Setting an adaptive threshold based on dynamically estimated background noise power;

[0027] Step 3.3: The triggering condition for synchronization point detection is: When , it is determined as a potential synchronization point; to avoid false triggering due to noise fluctuations, the power is required to continuously exceed the threshold for N sampling points before synchronization is confirmed;

[0028] Step 3.4: If the signal contains a known synchronization header, further accurately locate the synchronization point through cross-correlation after the power trigger. If there is a lag in the power trigger, adjust the synchronization point offset based on system parameters.

[0029] Furthermore, step 4 includes the following sub-steps:

[0030] Step 4.1: Coarse timing synchronization, find the starting position of the PSCCH subframe, specifically:

[0031] First, the autocorrelation of the received signal r[n] within the sliding window is calculated, as shown in formula (4):

[0032]

[0033] Among them, R[d] is the received signal sampling sequence, d is the number of sampling points between two adjacent DMRS symbols, m is the number of sampling points, N sym The number of sampling points between two adjacent DMRS symbols is determined by the OFDM symbol length and CP length;

[0034] Then find the autocorrelation peak d peak Position, that is, the starting position of the PSCCH subframe, as shown in formula (5):

[0035]

[0036] Step 4.2: Precise timing synchronization, using the frequency domain channel response of the DMRS to eliminate intra-symbol timing errors, specifically includes the following steps:

[0037] Step 4.2.1: Perform FFT on the synchronized DMRS symbol to extract the frequency domain pilot Y[k];

[0038] Step 4.2.2: Compare with the locally generated ideal DMRS sequence X[k] and calculate the channel response H[k], as shown in formula (6):

[0039]

[0040] Step 4.2.3: Perform IFFT on H[k] to obtain the time-domain channel impulse response h[n];

[0041] Step 4.2.4: Find the main path position n peak , as shown in formula (7):

[0042]

[0043] The main path position corresponds to the precise timing offset within the symbol, adjusting the sampling point alignment;

[0044] Furthermore, in step 5, the synchronization point is confirmed by majority voting, specifically:

[0045] For the i-th DMRS symbol of PSCCH, i=1,2,3,4, follow step 4.2 to get {n peak1 ,n peak2 ,n peak3 ,n peak4}, the synchronization point that appears the most times is taken as the final synchronization point sync_point.

[0046] Beneficial technical effects brought about by the present invention:

[0047] The method of the present invention obtains the coarse synchronization point, fine synchronization point values, and the final synchronization point value. Compared with the traditional timing synchronization without downsampling, the method of the present invention can reduce the system load, especially when processing large amounts of data, which helps to avoid system overload and improve the stability and performance of the system. Since downsampling reduces the amount of data, data can be transmitted faster and the transmission efficiency is improved. This is very useful for remote data synchronization or data transmission under limited network bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is an overall flow chart of a synchronization point calculation method based on LTE-V2X in the present invention;

[0049] Figure 2 This is a flowchart of LTE-V2X coarse synchronization in the present invention;

[0050] Figure 3 This is a flowchart of LTE-V2X fine synchronization in the present invention; DETAILED DESCRIPTION

[0051] The specific implementation of the present invention will be further described below with reference to specific embodiments:

[0052] A synchronization point calculation method based on LTE-V2X, such as Figure 1 As shown, the following steps are included:

[0053] Step 1: Obtain LTE-V2X baseband signal data;

[0054] Step 2: Calculate the number of RBs and RB offsets for PSCCH and PSSCH channels through blind detection.

[0055] Step 3: Use power trigger to calculate the coarse synchronization point, such as Figure 2 As shown, it includes the following sub-steps:

[0056] Step 3.1: Calculate the instantaneous power of the signal, specifically:

[0057] For the received signal Y[n], calculate the instantaneous power P[n] at each sampling point, as shown in formula (1):

[0058] P[n]=|Y[n]| 2 =Real(Y[n]) 2 +Imag(Y[n]) 2 (1)

[0059] Calculate the short-time average power of the signal, specifically:

[0060] The power is smoothed by a sliding window (such as a rectangular window of length L) to reduce the influence of noise, as shown in formula (2):

[0061]

[0062] in, is the short-time average power of the signal, L is the length of the rectangular window, P[nk] is the instantaneous power of the nkth sampling point, and n is the sequence number of the current sampling point;

[0063] Step 3.2: Set the empirical threshold, specifically:

[0064] According to the statistical characteristics of noise power (idle period) and signal power, the threshold T is set as shown in formula (3):

[0065]

[0066] in, is the empirical coefficient (such as 3 to 10), is the noise power;

[0067] Improve robustness by setting adaptive thresholds based on dynamically estimated background noise power (e.g., using the silent period of the signal preamble);

[0068] Step 3.3: Synchronization point detection;

[0069] The trigger condition is: When , it is determined to be a potential synchronization point;

[0070] Anti-shake processing: To avoid false triggering due to noise fluctuations, the power must exceed the threshold for N sampling points before synchronization is confirmed;

[0071] Step 3.4: Accurate synchronization correction;

[0072] Correlation peak assistance: If the signal contains a known synchronization header, the synchronization point can be further accurately located through cross-correlation after power triggering;

[0073] Delay compensation: If there is a lag in the power trigger, the synchronization point offset needs to be adjusted according to the system parameters.

[0074] Step 4: Use the PSCCH 4 DMRS sequences to calculate the precise synchronization point, such as Figure 3 As shown, it includes the following sub-steps:

[0075] Step 4.1: Coarse timing synchronization, find the starting position of the PSCCH subframe, specifically:

[0076] Use the time domain periodicity of DMRS to perform autocorrelation detection, and then find the autocorrelation peak position, that is, the starting position of the PSCCH subframe;

[0077] First, the autocorrelation of the received signal r[n] within the sliding window is calculated, as shown in formula (4):

[0078]

[0079] Among them, R[d] is the received signal sampling sequence, d is the number of sampling points between two adjacent DMRS symbols, m is the number of sampling points, N sym is the number of sampling points between two adjacent DMRS symbols, which is determined by the OFDM symbol length and the CP length; L is the correlation window length (usually the CP length or the DMRS symbol length).

[0080] Then find the autocorrelation peak d peak Position, that is, the starting position of the PSCCH subframe, as shown in formula (5):

[0081]

[0082] Step 4.2: Precise timing synchronization, using the frequency domain channel response of the DMRS to eliminate intra-symbol timing errors, specifically includes the following steps:

[0083] Step 4.2.1: Perform FFT on the synchronized DMRS symbol to extract the frequency domain pilot Y[k];

[0084] Step 4.2.2: Compare with the locally generated ideal DMRS sequence X[k] and calculate the channel response H[k], as shown in formula (6):

[0085]

[0086] Step 4.2.3: Perform IFFT on H[k] to obtain the time-domain channel impulse response h[n];

[0087] Step 4.2.4: Find the main path position n peak , as shown in formula (7):

[0088]

[0089] The main path position corresponds to the precise timing offset within the symbol, which adjusts the sampling point alignment.

[0090] Step 5: Calculate the final synchronization point of LTE-V2X;

[0091] The synchronization point is confirmed by majority vote, specifically:

[0092] For the i-th DMRS symbol of PSCCH, i=1,2,3,4, follow step 4.2 to get {n peak1 ,n peak2 ,n peak3 ,n peak4}, the synchronization point that appears the most times is taken as the final synchronization point sync_point.

[0093] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A synchronization point calculation method based on LTE-V2X, characterized by: The steps include: Step 1: Obtain LTE-V2X baseband signal data; Step 2: Calculate the number of RBs and RB offsets for PSCCH and PSSCH channels through blind detection. Step 3: Calculate the coarse synchronization point using power triggering; Step 4: Calculate the precise synchronization point using the PSCCH 4 DMRS sequences; Step 5: Calculate the final synchronization point of LTE-V2X.

2. The synchronization point calculation method based on LTE-V2X according to claim 1, characterized in that: Step 3 includes the following sub-steps: Step 3.1: Calculate the instantaneous power of the signal, specifically: For the received signal Y[n], calculate the instantaneous power P[n] at each sampling point, as shown in formula (1): P[n]=|Y[n]| 2 =Real(Y[n]) 2 +Imag(Y[n]) 2 (1) Calculate the short-time average power of the signal, specifically: The power is smoothed by sliding the window to reduce the influence of noise, as shown in formula (2): in, is the short-time average power of the signal, L is the length of the rectangular window, P[nk] is the instantaneous power of the nkth sampling point, and n is the sequence number of the current sampling point; Step 3.2: Set the empirical threshold, specifically: According to the statistical characteristics of noise power and signal power, the threshold T is set as shown in formula (3): in, is the empirical coefficient, is the noise power; Setting an adaptive threshold based on dynamically estimated background noise power; Step 3.3: The triggering condition for synchronization point detection is: When , it is determined as a potential synchronization point; to avoid false triggering due to noise fluctuations, the power is required to continuously exceed the threshold for N sampling points before synchronization is confirmed; Step 3.4: If the signal contains a known synchronization header, further accurately locate the synchronization point through cross-correlation after the power trigger. If there is a lag in the power trigger, adjust the synchronization point offset based on system parameters.

3. The synchronization point calculation method based on LTE-V2X according to claim 1, characterized in that: Step 4 includes the following sub-steps: Step 4.1: Coarse timing synchronization, find the starting position of the PSCCH subframe, specifically: First, the autocorrelation of the received signal r[n] within the sliding window is calculated, as shown in formula (4): Among them, R[d] is the received signal sampling sequence, d is the number of sampling points between two adjacent DMRS symbols, m is the number of sampling points, N sym The number of sampling points between two adjacent DMRS symbols is determined by the OFDM symbol length and CP length; Then find the autocorrelation peak d peak Position, that is, the starting position of the PSCCH subframe, as shown in formula (5): Step 4.2: Precise timing synchronization, using the frequency domain channel response of the DMRS to eliminate intra-symbol timing errors, specifically includes the following steps: Step 4.2.1: Perform FFT on the synchronized DMRS symbol to extract the frequency domain pilot Y[k]; Step 4.2.2: Compare with the locally generated ideal DMRS sequence X[k] and calculate the channel response H[k], as shown in formula (6): Step 4.2.3: Perform IFFT on H[k] to obtain the time-domain channel impulse response h[n]; Step 4.2.4: Find the main path position n peak , as shown in formula (7): The main path position corresponds to the precise timing offset within the symbol, which adjusts the sampling point alignment.

4. The synchronization point calculation method based on LTE-V2X according to claim 3, characterized in that: In step 5, the synchronization point is confirmed by majority voting, specifically: For the i-th DMRS symbol of PSCCH, i=1,2,3,4, follow step 4.2 to get {n peak1 ,n peak2 ,n peak3 ,n peak4 }, the synchronization point that appears the most times is taken as the final synchronization point sync_point.

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