An inter-cabin OFDM wireless communication system frame synchronization method and a frame synchronization detection module

Abstract

The application discloses a kind of inter-cabin OFDM wireless communication system frame synchronization method and frame synchronization detection module.Frame synchronization is the first step of receiver demodulator baseband processing, i.e.to carry out frame header detection to received wireless signal, determine the starting position of frame using preamble physical characteristics, to detect the arrival of valid data packet.Preamble is known short training sequence for transceiver, and frame synchronization detection is carried out using its good correlation characteristics and repeatability characteristics, and local correlation and autocorrelation processing are carried out on input signal in receiving end, and threshold value is compared in a manner, threshold value is greater than threshold value for many times, peak value is generated, and the interval between peak value is a group of short training sequence length, i.e.to consider that frame start is found, and accurate frame synchronization process is completed.Accuracy of frame synchronization directly affects OFDM symbol positioning performance, and its synchronization performance is the key to affect normal work of demodulator.

Description

TECHNICAL FIELD

[0001] The application discloses an inter-cabin OFDM wireless communication system frame synchronization method and a frame synchronization detection module, and belongs to the field of wireless communication signal processing. BACKGROUND

[0002] The inter-cabin data transmission usually adopts a slip ring electrical signal transmission mode. However, the slip ring has the following problems in use: (1) the service life is easily affected by the rotating wear and deformation; (2) the slip ring has the inherent characteristic of instantaneous open circuit, and has unreliable factors. For high-speed (such as more than 20 Mbps) data transmission requirements, the data communication interruption, frame loss and packet loss caused by the instantaneous open circuit characteristic of the slip ring will be very obvious.

[0003] In view of the above problems possibly existing in the slip ring communication and the demand for high-speed and reliable data transmission, the OFDM multicarrier modulation and demodulation processing technology is combined on the basis of the traditional coding and modulation processing. The OFDM signal transceiving is realized through an antenna, a wireless transmission link is formed, the rate bottleneck and communication interruption problem of the traditional slip ring wired link are effectively solved, and the system anti-multipath performance and reliability are improved.

[0004] The inter-cabin receiver receives the OFDM signal through an antenna, first filters and extracts the input signal, restores the baseband sample data, sends the baseband data to a demodulator for frame synchronization, and determines the frame start. According to the data transmission frame format characteristics, the continuous symbol sequence correlation characteristics in the known physical frame header are fully utilized for accurate detection, and then OFDM demodulation and decoding are performed and the result is output. Therefore, it can be seen that the frame synchronization detection is the key to the subsequent OFDM demodulation and decoding. SUMMARY

[0005] The technical solution of the application is to overcome the shortcomings of the prior art, provide an inter-cabin OFDM wireless communication system frame synchronization method and a frame synchronization detection module, solve the physical frame header frame synchronization problem of the inter-cabin OFDM receiver in a low signal-to-noise ratio and interference environment, accurately determine the frame start position, and reduce the false synchronization and OFDM symbol synchronization performance loss.

[0006] The technical solution of the application is: an inter-cabin OFDM wireless communication system frame synchronization method, which comprises the following steps:

[0007] S1, storing the received input signal to a buffer and performing complex conjugate correlation with the repeated short training sequence in the preamble, accumulating and summing the complex conjugate correlation results in the observation window period to obtain the correlation value in the observation window period;

[0008] S2, accumulating and summing the energy of the input signal in the observation window period to obtain the energy value in the observation window period;

[0009] S3, calculate the ratio of the local correlation value in the observation window period and the square of the energy value in the observation window period, and record the ratio as a discrimination value;

[0010] S4, compare the discrimination value with a preset threshold value, if the discrimination value is greater than the preset threshold value, it is considered that the discrimination value generates a peak value, and the position of the input signal corresponding to the peak value in the buffer is recorded;

[0011] S5, repeat steps S1-S4 until M peak values are generated, and compare the difference between the positions of the input signals corresponding to adjacent peak values in the buffer with a group of short training sequence lengths, if the difference is a group of short training sequence lengths, it is considered that the frame start is found, and the accurate frame synchronization is completed, and M is greater than or equal to 1.

[0012] Preferably, the observation window period is continuous N preamble periods, 1≤M≤L-N, and L is the number of groups of continuous repeated short training sequences in the preamble.

[0013] Preferably, the frame start position is:

[0014] The position of the Mth peak value in the buffer is (M-1+N)×a group of short training sequence lengths.

[0015] Preferably, the preset threshold value is 0.45-0.55.

[0016] Preferably, the energy of the input signal is calculated by calculating the modulus value of the input signal and squaring.

[0017] Another technical scheme of the present application is a frame synchronization detection module of an inter-cabin OFDM wireless communication system, the detection module comprising a local correlation branch, a self-correlation branch and a decision module.

[0018] The local correlation branch performs complex conjugate correlation summation on the input signal and the short training sequence in the preamble stored in the buffer within the observation window period, then calculates the modulus fourth power of the local correlation value in the observation window period to obtain the correlation value in the observation window period.

[0019] The self-correlation branch calculates the energy value of the input signal in the window period.

[0020] The decision module records the ratio of the correlation value in the observation window period and the energy value as a discrimination value, compares the discrimination value with a preset threshold value, if the discrimination value is greater than the preset threshold value, it is considered that the discrimination value generates a peak value, and the position of the input signal corresponding to the peak value in the buffer is recorded, the difference between the positions of the input signals corresponding to adjacent peak values in the buffer is compared with a group of short training sequence lengths, if the difference is a group of short training sequence lengths, it is considered that the frame start is found, and the accurate frame synchronization is completed, M is greater than or equal to 1, 1≤M≤L-N, and L is the number of groups of continuous repeated short training sequences in the preamble.

[0021] Preferably, the observation window period is continuous N preamble periods, 1≤M≤L-N, L is the number of groups of continuous repeated short training sequences in the preamble.

[0022] Preferably, the preset threshold is 0.45-0.55.

[0023] Preferably, the energy of the received input signal is calculated by calculating the modulus of the input signal and squaring.

[0024] Preferably, the frame start position is:

[0025] The Mth peak corresponds to the position -(M-1+N)×a group of short training sequence lengths in the cache.

[0026] The present application has the following advantages compared with the prior art:

[0027] The present application aims at multiple continuous correlation peak points that may occur in the frame synchronization processing process, the peak points are all greater than the threshold, and the peak points are separated by a group of short training sequence sample points. By judging whether the interval sample points between the multiple continuous correlation peak points greater than the threshold meet the above characteristics, the false synchronization judgment can be strengthened, the frame synchronization accuracy can be improved, and the receiver synchronization demodulation performance can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The figure is a wireless communication physical frame structure block diagram of the embodiment of the present application.

[0029] Figure 2 The figure is a local correlation and autocorrelation two-branch comparison threshold block diagram of the embodiment of the present application.

[0030] Figure 3 The figure is a frame synchronization implementation block diagram of the embodiment of the present application.

[0031] Figure 4 The figure is a frame synchronization simulation effect block diagram of the embodiment of the present application.

[0032] Figure 5 The figure is a multiple continuous peak point characteristic block diagram of the embodiment of the present application. DETAILED DESCRIPTION

[0033] The present application will be further described below in combination with the drawings.

[0034] The application provides a frame synchronization method and a frame synchronization detection module for an inter-cabin wireless communication system. In the inter-cabin wireless communication system, the OFDM modulation and demodulation technology is usually used due to the complex closed and semi-closed application environment inside and outside the satellite cabin and the influence of multipath interference. In order to accurately locate the OFDM symbol for subsequent OFDM demodulation, the receiving end needs to complete the accurate frame synchronization process first. The frame synchronization is the first step of the baseband processing of the receiver demodulator, that is, the frame header detection of the received wireless signal is performed, the starting position of the frame is determined by using the physical characteristics of the preamble, and the arrival of the effective data packet is detected. The preamble is composed of a short training sequence known by the transceiver, and the transceiver is known. The receiving end can use the good correlation characteristics and the repetitive characteristics for frame synchronization detection. The input signal is processed by local correlation and autocorrelation in the receiving end, and the threshold value is compared. When the threshold value is greater than the threshold value for multiple times, a peak value is generated, and the interval between the peak values is a group of short training sequence lengths. It is considered that the frame starting point is found, and the accurate frame synchronization process is completed.

[0035] As shown in Figure 1 In a specific embodiment of the application, the inter-cabin wireless transmission physical frame structure is composed of a preamble, signaling and an effective data field. In order to better complete the frame synchronization, the training sequence with good correlation performance is selected to form the preamble, including a short training sequence and a long training sequence. The short training sequence L-STF is composed of ten groups of identical symbols: STS1-STS10. The data field is composed of an integer OFDM symbol of payload data and padding data.

[0036] The application provides an inter-cabin OFDM wireless communication system frame synchronization method, which comprises the following steps:

[0037] S1, the received input signal is stored in the buffer and is complex conjugate correlated with the repeated short training sequence in the preamble. The complex conjugate correlation results in the observation window period are accumulated and summed to obtain the correlation value in the observation window period.

[0038] S2, the energy of the input signal in the observation window period is accumulated and summed to obtain the energy value in the observation window period. The energy of the received input signal is calculated by calculating the modulus value of the input signal and squaring.

[0039] S3, the ratio of the modulus fourth power of the local correlation value in the observation window period to the square of the energy value in the observation window period is calculated, and is recorded as a discrimination value.

[0040] S4, the discrimination value is compared with the preset threshold value. If the discrimination value is greater than the preset threshold value, it is considered that the discrimination value generates a peak value, and the position of the input signal corresponding to the peak value in the buffer is recorded.

[0041] S5, repeating steps S1-S4 until M peaks appear, comparing the difference between the positions of the input signals corresponding to adjacent peaks in the buffer in the M peaks to see if the difference is the length of a group of short training sequences, if so, it is considered that the frame start is found, and the accurate frame synchronization is completed, and M is greater than or equal to 1.

[0042] The observation window period is a continuous N preamble period, 1≤M≤L-N, and L is the number of groups of short training sequences continuously repeated in the preamble.

[0043] The frame start position is:

[0044] The position corresponding to the Mth peak in the buffer is (M-1+N)×the length of a group of short training sequences.

[0045] As shown in Figure 2 In a specific embodiment of the present application, a method of comparing thresholds in two branches of local correlation and autocorrelation is adopted, the local correlation branch is the complex conjugate correlation sum of the input signal and the local known data in the window period, and the fourth power of the local correlation value in the window period is calculated; the autocorrelation branch is the square of the modulus value of the input signal, and the energy sum of the input signal in the window period is obtained, and the square of the energy value in the window period is calculated; finally, the data interval between the peaks is continuously and slidingly judged to be fixed to accurately synchronize the frame start.

[0046] Based on the above method, the present application further provides a frame synchronization detection module for an inter-cabin OFDM wireless communication system, which comprises a local correlation branch, an autocorrelation branch, and a decision module;

[0047] The local correlation branch is to perform complex conjugate correlation sum on the input signal and the short training sequence in the preamble stored in the buffer in the observation window period, and calculate the fourth power of the local correlation value in the window period to obtain the correlation value in the observation window period.

[0048] The autocorrelation branch is to calculate the energy value of the input signal in the window period, and the energy of the input signal is calculated by calculating the square of the modulus value of the input signal.

[0049] The decision module records the ratio of the correlation value in the observation window period to the energy value as a discrimination value, compares the discrimination value with a preset threshold, if the discrimination value is greater than the preset threshold, it is considered that the discrimination value produces a peak, the position of the input signal corresponding to the peak in the buffer is recorded, the difference between the positions of the input signals corresponding to adjacent peaks in the M peaks is compared to see if the difference is the length of a group of short training sequences, if so, it is considered that the frame start is found, and the accurate frame synchronization is completed, M is greater than or equal to 1, 1≤M≤L-N, and L is the number of groups of short training sequences continuously repeated in the preamble.

[0050] The observation window period is a continuous N preamble period, 1≤M≤L-N, and L is the number of groups of short training sequences continuously repeated in the preamble.

[0051] The preset threshold is 0.45 to 0.55.

[0052] The frame start position is:

[0053] The Mth peak corresponds to a position in the cache that is -(M-1+N) × the length of a short training sequence.

[0054] like Figure 3 As shown, in a specific embodiment of the present invention, frame synchronization detection mainly consists of two branches: buffering, local correlation, and autocorrelation, as well as a decision module. It mainly involves operations such as buffering, correlation, summation, modulo 4, and energy square. Given that a set of short training sequence STS symbols has 16 sample data points, a sharp correlation peak will appear after 16 sample data points. If a set of known symbols is used to perform sliding correlation with 10 sets of repeated STS, 10 sharp correlation peaks will appear consecutively, with an interval of 16 sample data points between the peaks. Window C is the complex conjugate correlation between the received input signal and the local short training sequence data. The sample length is four groups of 4*STS symbols, with a length of 4*16=64. The sum is accumulated and then the modulus is raised to the fourth power. Window P is the energy calculation for the autocorrelation of the received signal. The sum is accumulated and squared, and the sample length is the same as that of window C. The ratio of the two is used and compared with a threshold of 0.5. The comparison is not based on a single value being greater than the threshold. The sliding continues until the threshold is found to be greater than 0.5 three times in a row. The peak position is recorded each time. It is determined whether the difference between the three sequence numbers is D, where D is the length of a set of STS sequence samples, which is 16 in this case. The frame synchronization detection is then considered complete. The buffer is backtracked to determine the start position of the entire frame and output it.

[0055] Frame start position = position in buffer corresponding to the Mth peak - (M-1+N)×D, where in this example M=3, N=4, D=16.

[0056] like Figure 4 As shown, using the local 4 sets of STS as the correlation window, after frame synchronization processing with the received data, the decision threshold will show 7 sets of very high sharp peaks in 10 consecutive short training sequence positions. The comparison threshold on both sides will decrease successively. In other data segments, the correlation comparison threshold is very low and there are no peaks. At this time, the threshold decision threshold is set to 0.5.

[0057] like Figure 5 As shown, within the threshold range, the seven related peaks all satisfy the characteristic of being 16 sample data points apart (the length of a set of STS data). This continuous feature can be used to strengthen the judgment of missynchronization and determine the accuracy of frame synchronization.

[0058] In summary, the method of the application adopts the processing mode that the local correlation and the autocorrelation two branches are compared with the threshold value and are greater than the threshold value; the local correlation branch is the complex conjugate correlation summation of the input signal and the local known data in the window period, and the fourth power of the local correlation value in the window period is calculated; the autocorrelation branch is the modulus value of the input signal and the square, and the energy sum of the input signal in the window period is obtained, and the square of the energy value in the window period is calculated; the method can continuously appear multiple correlation peak points, and the peak points are different by a group of STS sample intervals, the difference sample number between the correlation peak values greater than the threshold value for multiple times is determined, the false synchronization judgment is strengthened, the frame synchronization accuracy is determined, and the synchronization demodulation performance of the receiving end is met under the condition of low signal-to-noise ratio.

Claims

1. An inter- cabin OFDM wireless communication system frame synchronization method, characterized by It comprises the following steps: S1, store the received input signal to the buffer and perform complex conjugate correlation with the repeated short training sequence in the preamble, accumulate and sum the complex conjugate correlation results in the observation window period to obtain the correlation value in the observation window period; S2, accumulate and sum the energy of the input signal in the observation window period to obtain the energy value in the observation window period; S3, calculate the ratio of the local correlation value in the observation window period to the square of the energy value in the observation window period, and record it as the discrimination value; S4, compare the discrimination value with the preset threshold value, if the discrimination value is greater than the preset threshold value, it is considered that the discrimination value produces a peak value, and the position of the input signal corresponding to the peak value in the buffer is recorded; S5, repeat steps S1-S4 until M peak values appear, compare the difference between the positions of the input signals corresponding to adjacent peak values in the buffer, if it is a group of short training sequence length, it is considered that the frame start is found, and the accurate frame synchronization is completed, M is greater than or equal to 1.

2. The method of Claim 1, wherein The observation window period is continuous N preamble periods, 1≤M≤L-N, and L is the number of groups of continuous repeated short training sequences in the preamble.

3. The method of Claim 1, wherein The frame start position is: The position of the Mth peak value in the cache-(M-1+N)×a group of short training sequence length.

4. The method of Claim 1, wherein The preset threshold value is 0.45-0.

55.

5. The method of Claim 1, wherein The energy of the received input signal is calculated by calculating the modulus value of the input signal and squaring.

6. An inter- cabin OFDM wireless communication system frame synchronization detection module characterized by It comprises a local correlation branch, an autocorrelation branch and a decision module; The local correlation branch, the input signal is correlated with the short training sequence in the preamble stored in the buffer and summed in the observation window period, and the modulus fourth power of the local correlation value in the window period is calculated to obtain the correlation value in the observation window period; The autocorrelation branch, the energy value of the input signal in the window period; The decision module, the ratio of the correlation value in the observation window period to the energy value is recorded as the discrimination value, the discrimination value is compared with the preset threshold value, if the discrimination value is greater than the preset threshold value, it is considered that the discrimination value produces a peak value, and the position of the input signal corresponding to the peak value in the buffer is recorded, the difference between the positions of the input signals corresponding to adjacent peak values in the buffer is compared, if it is a group of short training sequence length, it is considered that the frame start is found, and the accurate frame synchronization is completed, M is greater than or equal to 1, 1≤M≤L-N, and L is the number of groups of continuous repeated short training sequences in the preamble.

7. The frame synchronization detection module for inter- cabin OFDM wireless communication system of claim 6, wherein, The observation window period is continuous N preamble periods, 1≤M≤L-N, and L is the number of groups of continuous repeated short training sequences in the preamble.

8. The frame synchronization detection module for inter- cabin OFDM wireless communication system of claim 6, wherein, The preset threshold value is 0.45-0.

55.

9. The frame synchronization detection module for inter- cabin OFDM wireless communication system of claim 6, wherein, The energy of the received input signal is calculated by calculating the modulus value of the input signal and squaring.

10. The frame synchronization detection module for inter- cabin OFDM wireless communication system of claim 6, wherein, The frame start position is: The position of the Mth peak value in the cache-(M-1+N)×a group of short training sequence length.

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