A two-branch synchronization method applicable to medium-voltage carrier systems

Abstract

The present invention provides a two-diversity synchronization method applicable to a medium-voltage carrier system. A linear frequency modulation signal is used as a synchronization symbol, and opposite polarities are represented by different phases. The channel signal-to-noise ratio is improved through the concept of diversity, and the synchronization law is obtained by solving the correlation coefficients of two adjacent sliding windows at the receiving end to verify whether synchronization is triggered. Through the improved synchronization process, the present invention improves the synchronization performance, can meet the communication limit under the current single-subcarrier state, and enables the synchronization not to restrict the overall application of the OFDM system.

Description

Technical Field

[0001] The present invention belongs to the technical field of power line communication, and particularly relates to a two-diversity synchronization method applicable to a medium-voltage carrier system. Background Art

[0002] At present, the power line communication field has advanced to multi-carrier modulation technology. The OFDM (Orthogonal Frequency Division Multiplexing) technology has received extensive attention due to its many advantages such as high spectrum utilization rate and strong anti-interference ability. The performance of the OFDM system has been improved for a relatively long time at present, and the performance has approached the best ideal state. Compared with the single-carrier state, the synchronization performance has become the key problem restricting the performance of the OFDM system, which requires the system to improve the performance in terms of synchronization problems.

[0003] There are mainly four ways to achieve OFDM synchronization: 1. Maximum likelihood estimation of frequency offset. Assuming that timing synchronization has been completed, by transmitting two identical OFDM blocks, the maximum likelihood function can be obtained according to the properties of the FFT. However, the capture range of this maximum likelihood estimation is ±1 / 2 sub-carrier interval. If the capture range is to be increased, the synchronization accuracy must be sacrificed. 2. Estimate timing synchronization based on pilot symbols and cyclic prefix. Since the OFDM system uses pilot symbols for channel estimation, pilot symbols and cyclic prefix are simultaneously used for timing estimation. At the same time, for the case of high signal-to-noise ratio, the estimation mainly depends on the cyclic prefix; for the case of low signal-to-noise ratio, it mainly depends on the pilot symbols. 3. Use the cyclic prefix to achieve symbol boundary synchronization. The introduction of the cyclic prefix (Cyclic Prefix) is an important feature of the OFDM system. Its basic idea is to form a guard interval by introducing a cyclic prefix, thereby effectively combating ISI and ICI caused by multipath delay. The method is to insert the latter part of the OFDM symbol into the beginning part of the symbol in the time domain to form a cyclic prefix. The length of the guard interval should be greater than the maximum multipath delay spread. One type is to subtract the received signal delayed by N sampling points from the received signal. Using the properties of the cyclic prefix, the result after subtraction should be approximately zero in a specific time period. Then, timing synchronization is completed using this property. Another type is to use the correlation between the cyclic prefix and the signal separated by N sampling points to obtain a joint estimation of timing and frequency offset. 4. Use special training symbols for synchronization. The synchronization technology based on the cyclic prefix is very suitable for tracking or self-synchronization, and there are no special training symbols available at this time. For packet transmission, there are great disadvantages because accurate synchronization requires averaging a large number of OFDM symbols to obtain correlation peaks and appropriate signal-to-noise ratio SNR. In high-speed packet transmission, the synchronization time requirement is as short as possible, preferably only equivalent to the time length of a few OFDM symbols. To achieve this, special training symbols with known data for the receiving end can be used to achieve synchronization through the received complete training symbols. Summary of the Invention

[0004] To solve the deficiencies or defects existing in the above-mentioned prior art, the present invention proposes a two-branch synchronization method applicable to medium-voltage carrier systems, which improves the signal-to-noise ratio through diversity, increases the synchronization success rate under low signal-to-noise ratio, and at the same time eliminates the state where some synchronization symbols are not diversified during the two-branch process through a special arrangement and combination method. To achieve the purpose of overall improving the synchronization success rate.

[0005] To achieve the above purpose, the present invention provides a two-branch synchronization method applicable to medium-voltage carrier systems, including the following steps:

[0006] Step 1: The synchronization signal used at the transmitting end of the carrier machine is a linear frequency modulation signal. The transmitting end generates a synchronization signal with a length of 9 symbols.

[0007] Step 2: At the receiving end, two-branch diversity processing is performed on the received noise and signal in real time. The two-branch diversity is implemented through two non-adjacent sliding windows. The length of the two sliding windows is one symbol, and the distance between them is one symbol. The data after two-branch diversity processing is obtained by summing the data within the two sliding windows separated by one symbol length.

[0008] The principle is as follows: The synchronization signal uses the same linear frequency modulation signal, and the polarities of the symbols of different signals are different. The phase inversion is represented by 1 and -1. The two synchronization signals with the same polarity are added to obtain a linear frequency modulation signal with twice the amplitude; the noise in the system is all Gaussian distributed random noise, and the added noise amplitude after adding two independent segments of noise does not show an accumulative result; the signal-to-noise ratio of the synchronization signal is improved through the above two-branch diversity processing.

[0009] The principle of two-branch diversity is as follows. Before two-branch diversity, the signal-to-noise ratio SNR of the synchronization signal is as follows:

[0010] ,

[0011] For the synchronized data after two-branch diversity processing, the formula for the increased signal-to-noise ratio is as follows:

[0012] ,

[0013] is the amplitude of the signal, is the scale parameter of the noise,

[0014] However, the signal after two-branch diversity generates 9 synchronization headers with low signal-to-noise ratio before and after the new synchronization header. In order to avoid the superposition of noise and signal to generate "small signals" with low signal-to-noise ratio, the polarity arrangement of the newly designed new synchronization sequence is: [0, 0, 1, 1, -1, 1, -1, 1 -1, 1, 1, 0, 0], where 0 represents noise and carrier data, and its polarity is not restricted.

[0015] Considering the distinction of uplink and downlink communication synchronization, the polarity arrangement of the new synchronization sequence for the two-branch diversity scheme of downlink communication is [0, 0, -1, 1, 1, 1, 1, 1, 1, 1, -1, 0, 0];

[0016] The superposition method of the two branches is the sliding accumulation of the front and rear windows. There is a symbol length distance between the two windows. The arrangement of the synchronization header after the two branches is [1, 1, 0, 1, -1, 1, -1, 1, 0, 1, 1]. Among them, the amplitudes of the first four and the last four synchronization headers with polarity 1 are the same as those of the original synchronization header, and the amplitudes of the remaining synchronization header symbols are twice the original amplitude;

[0017] The arrangement of the corresponding synchronization header after the two branches of the downlink communication is [-1, 1, 0, 1, 1, 1, 1, 1, 0, 1, -1];

[0018] Step 3: At the receiving end, use the front and rear two adjacent sliding windows to solve the correlation coefficient of the two-branch data obtained in Step 2 in real time to verify whether the obtained rule conforms to the rule of successful synchronization. By solving the correlation coefficient of the front and rear two adjacent sliding windows, the length of the sliding window is one symbol length, and the two sliding windows are adjacent. The correlation coefficient solving formula is:

[0019]

[0020] X represents the window that is earlier in time; Y represents the later window, where is the covariance, which is simplified to XY, 2 , and the expression form used in the denominator in the present invention is .

[0021] Further, the rule obtained after obtaining the correlation coefficient in Step 3 is that when it satisfies more than the system-set time and is lower than the negative threshold or higher than the positive threshold, the synchronization is triggered successfully.

[0022] Further, the threshold is set to 0.1367, and it is considered that the synchronization is successful only when it satisfies being lower than the negative threshold or higher than the positive threshold for 4 consecutive symbol lengths.

[0023] The beneficial effects of the present invention are as follows: The present invention improves the signal-to-noise ratio through the diversity method, improves the synchronization success rate under low signal-to-noise ratio, and at the same time eliminates the state where some synchronization symbols do not have diversity during the two-branch process through a special arrangement and combination method. To achieve the purpose of overall improving the synchronization success rate. Description of the Drawings

[0024] Figure 1 is the flow chart of the present invention.

[0025] Figure 2 is the explanatory diagram of the newly designed synchronization sequence of the present invention.

[0026] Figure 3 is the explanatory diagram of the new synchronization sequence of the downlink communication of the present invention.

[0027] Figure 4This is an explanatory diagram of the synchronization header arrangement after the diversity of the present invention.

[0028] Figure 5 This is an explanatory diagram of the synchronization header arrangement after the diversity of the downlink communication of the present invention.

[0029] Figure 6 This is the final law diagram of the correlation coefficient obtained by the receiving end of the present invention.

[0030] Figure 7 This is a comparison diagram of the synchronization performance of the present invention and the existing synchronization performance effects. Specific embodiments

[0031] Next, in combination with the accompanying drawings in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0032] Embodiment:

[0033] As Figure 1 shown, the technical solution of the present invention is as follows:

[0034] Step 1: The synchronization signal used by the transmitting end of the carrier machine is a linear frequency modulation signal. A linear frequency modulation signal under the base frequency signal is used to generate a synchronization signal at the transmitting end, with a length of 9 symbols;

[0035] Step 2: At the receiving end, the received noise and signal are subjected to diversity processing in real time, and its implementation method needs to be completed through two non-adjacent sliding windows. The length of the two sliding windows is one symbol, and the distance is one symbol. The data after diversity processing is obtained by summing the data in the two sliding windows separated by one symbol length.

[0036] The principle is as follows: The synchronization signal uses the same linear frequency modulation signal. The difference between symbols lies in different polarities, and 1 and -1 are used to represent the phase inversion. Adding two synchronization signals with the same polarity can obtain a linear frequency modulation signal with twice the amplitude; for noise, the noise in the system is all random noise that satisfies the Gaussian distribution, and the added noise amplitude after adding two independent segments of noise will not show an accumulative result; after signal diversity processing, the purpose of enhancing the signal energy and reducing the noise energy can be achieved, and the comprehensive result is to improve the signal-to-noise ratio of the synchronization signal, so that it can achieve the performance of a high signal-to-noise ratio state under low signal-to-noise ratio conditions.

[0037] The principle of improving the diversity synchronization performance is as follows. Before diversity, the signal-to-noise ratio of the synchronization signal is as follows:

[0038]

[0039] The synchronized data after two-branch processing, and the formula for the increase in its signal-to-noise ratio is as follows:

[0040]

[0041] However, the two-branch will generate 9 synchronization headers with lower signal-to-noise ratios before and after the new synchronization header respectively (because these synchronization headers only accumulate noise and there is no signal accumulation). In order to avoid the "small signal" with low signal-to-noise ratio caused by the superposition of noise and signal, a new synchronization sequence is redesigned, as Figure 2 shown. Considering the distinction of uplink and downlink communication synchronization, the new synchronization sequence of the two-branch scheme for downlink communication is as Figure 3 shown. The specific two-branch superposition method is the sliding accumulation of the front and rear two windows, and there is a symbol length distance between the two windows. The arrangement method of the synchronization headers after two-branch is as Figure 4 shown. The arrangement method of the synchronization headers after two-branch corresponding to downlink communication is as Figure 5 shown.

[0042] Step 3: At the receiving end, use two adjacent sliding windows before and after to solve the correlation coefficient of the two-branch data obtained in Step 2 in real time to verify whether the obtained law conforms to the law of successful synchronization, which is obtained by solving the correlation coefficient of the two sliding windows. The length of the sliding window is one symbol length, and the two sliding windows are adjacent. The correlation coefficient solving formula is:

[0043]

[0044] where X represents the window that is earlier in time; Y represents the later window. The numerator is the covariance, which is simplified to XY. Currently, several common denominator expression forms in the literature are X 2 , Y 2 , . The expression form adopted by the denominator used in the present invention is .

[0045] Furthermore, if the law finally obtained after obtaining the correlation coefficient in Step 3 satisfies being lower than the negative threshold or higher than the positive threshold for a long time, then the synchronization is successful. The specific law schematic diagram is as Figure 6 shown..

[0046] Furthermore, the recognition of the relevant law mentioned in Step 3 at the receiving end is as Figure 6 shown. Its threshold is set to 0.1367, and it must satisfy being lower than the negative threshold or higher than the positive threshold for 4 consecutive symbol lengths (distinguishing uplink and downlink communication) to be considered as successful synchronization. The comparison of the synchronization performance after two-branch and without two-branch with the existing synchronization performance effect is as Figure 7As shown, it can be seen that the success rate of the signal after diversity is significantly improved compared to that of the signal without diversity.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Those of ordinary skill in the art can still modify or equivalently replace the specific implementation manners of the present invention with reference to the above embodiments. Any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention are within the scope of the claims of the present invention pending approval.

Claims

1. A two-branch synchronization method applicable to medium-voltage carrier systems, characterized in that, it includes the following steps: Step 1: The synchronization signal used by the transmitting end of the carrier machine is a linear frequency modulation signal. The transmitting end generates a synchronization signal with a length of 9 symbols; Step 2: At the receiving end, the received noise and signals are processed in real time by two branches. The two branches are implemented through two non-adjacent sliding windows. The length of the two sliding windows is one symbol, and the distance between them is one symbol. The data after two-branch processing is obtained by summing the data within the two sliding windows separated by one symbol length; The synchronization signal uses the same linear frequency modulation signal. The symbols of different signals have different polarities, and 1 and -1 are used to represent the phase inversion. Nine low signal-to-noise ratio synchronization headers are generated before and after the new synchronization header for the signal after two branches. To avoid the generation of "small signals" with low signal-to-noise ratio caused by the superposition of noise and signals, the polarity arrangement of the newly designed new synchronization sequence is: [0, 0, 1, 1, -1, 1, -1, 1, -1, 1, 1, 0, 0], where 0 represents noise and carrier data, and its polarity is not restricted; Considering the distinction of uplink and downlink communication synchronization, the polarity arrangement of the new synchronization sequence for the two-branch scheme of downlink communication is [0, 0, -1, 1, 1, 1, 1, 1, 1, 1, -1, 0, 0]; The superposition method of the two branches is the sliding accumulation of the front and rear two windows. There is a symbol length distance between the two windows. The arrangement of the synchronization headers after two branches is [1, 1, 0, 1, -1, 1, -1, 1, 0, 1, 1]. Among them, the amplitudes of the front and rear four synchronization headers with a polarity of 1 are the same as the amplitude of the original synchronization header, and the amplitudes of the remaining synchronization header symbols are twice the original amplitude; The corresponding arrangement of the synchronization headers after two branches of downlink communication is [-1, 1, 0, 1, 1, 1, 1, 1, 0, 1, -1]; Step 3: At the receiving end, the correlation coefficient is solved in real time using two adjacent sliding windows for the two-branch data obtained in Step 2 to verify whether the obtained law conforms to the law of successful synchronization. By solving the correlation coefficient for two adjacent sliding windows, the length of the sliding window is one symbol length, and the two sliding windows are adjacent. The correlation coefficient solving formula is: where ρ represents the correlation coefficient, X represents the data within the front window in terms of time, Y represents the data within the rear window, cov(·) represents the covariance calculation function, and D 2 (·) represents the variance calculation function.

2. A two-branch synchronization method applicable to medium-voltage carrier systems according to claim 1, characterized in that, the law obtained after obtaining the correlation coefficient in Step 3 is that the duration of the obtained correlation coefficient exceeds the duration set by the system, and when the theoretical correlation coefficient is 1, the obtained correlation coefficient is higher than the positive threshold, and when the theoretical correlation coefficient is -1, the obtained correlation coefficient is lower than the negative threshold, then it is considered that the synchronization is successful. The duration set by the system is the duration of the transmitted symbol.

3. A two-branch synchronization method applicable to medium-voltage carrier systems according to claim 1, characterized in that, the absolute value of the threshold is 0.1367, that is, the positive threshold is 0.1367 and the negative threshold is -0.1367. For uplink communication, it is considered that the synchronization is successful only when it continuously satisfies being lower than the negative threshold for 4 symbol lengths. For downlink communication, it is considered that the synchronization is successful only when it continuously satisfies being higher than the positive threshold for 4 symbol lengths.

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