WO2021022969A1 - 穿钢数能同传系统中数据传输链路符号定时同步的方法 - Google Patents

穿钢数能同传系统中数据传输链路符号定时同步的方法 Download PDF

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WO2021022969A1
WO2021022969A1 PCT/CN2020/101050 CN2020101050W WO2021022969A1 WO 2021022969 A1 WO2021022969 A1 WO 2021022969A1 CN 2020101050 W CN2020101050 W CN 2020101050W WO 2021022969 A1 WO2021022969 A1 WO 2021022969A1
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timing
symbol
steel
training sequence
transmission system
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French (fr)
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刘涛
李长林
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北京科技大学
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2602—Signal structure
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2662—Symbol synchronisation

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  • the invention relates to the technical field of ultrasonic communication, in particular to a method for symbol timing synchronization of a data transmission link in a steel-piercing digital energy simultaneous transmission system.
  • Ultrasound has the characteristics of low attenuation and high speed when it is transmitted in metal because of its good directionality and strong penetrating power. Therefore, ultrasonic waves can be used as the carrier of information transmission, and the metal channel can be used as the medium of information transmission to realize the transmission of data inside and outside the metal container.
  • the steel-piercing signal transmission system is a system established for the problem that traditional communication methods cannot be transmitted in thick metal walls. It breaks through the bottleneck of wired transmission communication and traditional radio frequency communication, and can be widely used in industrial fields.
  • Fig. 1 is a schematic diagram of ultrasonic communication through a metal plate.
  • This system includes: a transmitting transducer 1, a couplant 2, a metal wall 3, and a receiving transducer 4.
  • the transmitting transducer 1 on the left side of the metal wall 3 converts the electrical signal into an ultrasonic signal, the ultrasonic signal passes through the metal wall 3 to the receiving transducer 4 at the receiving end, and the receiving transducer 4 restores the ultrasonic signal to an electrical signal.
  • the transmitting transducer 1 and the receiving transducer 4 are symmetrically placed on both sides of the metal wall 3, and the transducer and the metal wall 3 are connected by a couplant 2.
  • FIG. 2 shows a schematic diagram of the basic architecture of the OFDM system.
  • the DSP module at the transmitter includes symbol modulation, inverse Fourier transform, cyclic prefix insertion, and up-conversion processes.
  • the input signal passes through the DSP at the transmitting end and then passes through the DAC module to obtain an analog signal.
  • the analog signal is converted into an ultrasonic signal through the metal wall by the transmitting transducer.
  • the DSP module at the receiving end includes symbol demodulation, Fourier transform, cyclic prefix removal, down-conversion and signal synchronization processes. After passing through the metal wall, the ultrasonic signal is converted into an electric signal by the receiving transducer on the other side. The electric signal passes through the peak-to-average power ratio suppression module and then passes through the low noise amplifier, and then obtains the output signal through the receiving end DSP.
  • OFDM has the advantages of high spectrum utilization, simple implementation, and effective resistance to frequency selective fading and multipath effects during signal transmission.
  • Each carrier in OFDM is orthogonal to each other.
  • Each carrier has an integer number of carrier periods in one symbol time.
  • the spectrum zero of each carrier overlaps with the zeros of adjacent carriers, which reduces the interference between carriers. Due to the partial overlap between the carriers, the frequency band utilization is improved.
  • the orthogonal sub-carriers in the OFDM system can be modulated and demodulated using fast Fourier transform.
  • the guard interval is added to the transmitting end of the OFDM system mainly to eliminate inter-symbol interference caused by multipath.
  • the method is to fill the cyclic prefix in the OFDM symbol guard interval, so that signals with a delay less than the guard interval will not cause inter-symbol interference during the demodulation process.
  • FIG. 3 is a schematic diagram of three situations of OFDM timing synchronization results, showing several possible situations of symbol timing deviation.
  • Case 1 The timing is accurate. In this case, the predicted starting point of the OFDM symbol is consistent with the precise position. The OFDM symbols can be recovered completely without introducing interference.
  • Case 3 Timing is lagging, in this case the predicted OFDM symbol start point is slightly later than the precise position.
  • the receiving end FFT window will cover part of the current OFDM symbol data and the next OFDM symbol cyclic prefix or part of the data. At this time, part of the data information will be lost.
  • the most serious thing is that the orthogonality between sub-carriers is destroyed, and then inter-symbol interference and inter-carrier interference are introduced into the system.
  • Figure 4 shows a schematic diagram of the traditional symbol timing synchronization Schmidl&D.Cox algorithm measurement function curve.
  • Schmidl and D. Cox, etc. designed a training sequence with the same first half and second half, which combined with related operations to complete OFDM symbol synchronization.
  • d is the first time sample corresponding to the sliding window
  • the total length of the training sequence is N
  • the length of the sequence symbol L is both N/2
  • the received signal is r(d)
  • r * (d) and r(d) is mutually conjugate
  • P sc (d) is the correlation summation formula
  • R sc (d) is the energy value of the second half of the sequence.
  • Figure 5 is a schematic diagram of another traditional symbol timing synchronization Minn algorithm metric function curve.
  • Minn et al. improved the structure of the training sequence in response to the "peak plateau" problem in the Schmidl&D.Cox algorithm.
  • d is the first time sample corresponding to the sliding window
  • the total length of the training sequence is N
  • the length L of the sequence symbols is N/4
  • -B is the negative structure of B.
  • the purpose of the present invention is to provide a method for synchronizing the symbol timing of a data transmission link in a steel-penetrating energy simultaneous transmission system, which mainly solves the symbol timing problem, thereby improving the overall performance of the steel-penetrating energy simultaneous transmission system.
  • the embodiment of the present invention provides a method for symbol timing synchronization of data transmission links in a steel-through data transmission system, which includes the following steps:
  • the structure of the training sequence includes symbol differences and conjugate relationships
  • the structure of the training sequence is:
  • the total length of the training sequence is N
  • the length L of each sequence symbol is N/4
  • B is conjugate with A
  • -A and -B are negative structures of A and B, respectively.
  • the timing measurement calculation is performed by the following formula:
  • d is the first time sample value corresponding to the sliding window
  • r * (d) and r(d) are conjugate each other
  • P g (d) is the value of the related item in the sequence symbol
  • R g (d) is The energy value of the training sequence.
  • the method further includes:
  • an adaptive threshold based on the real-time signal power value is used for boundary judgment.
  • the step of boundary judgment includes:
  • the method further includes:
  • timing mean square error function MSE Use the timing mean square error function to evaluate the performance of the algorithm.
  • the timing mean square error function MSE is defined as follows:
  • n is the number of simulations
  • observed m represents the m-th observation value
  • set m represents the m-th actual set value
  • the invention designs a new training sequence structure and proposes a new timing measurement calculation method, which solves the platform effect of the Schmidl&D.Cox algorithm and the large synchronization error of the Minn algorithm, improves the accuracy of timing synchronization, and improves the number of steel penetrations.
  • the symbol timing synchronization problem of the data link in the simultaneous transmission system can improve the overall performance of the simultaneous transmission system.
  • Figure 1 is a schematic diagram of ultrasonic communication through a metal plate
  • FIG. 2 is a schematic diagram of the basic architecture of an OFDM system
  • Figure 3 is a schematic diagram of three situations of OFDM timing synchronization results
  • Figure 4 is a schematic diagram of the metric function curve of the Schmidl&D.Cox algorithm
  • Figure 5 is a schematic diagram of the metric function curve of the Minn algorithm
  • Figure 6 is a flowchart of a method for symbol timing synchronization of data transmission links in a steel-through data transmission system provided by an embodiment of the present invention
  • FIG. 7 is a schematic diagram of a synchronization symbol structure of a training sequence in an embodiment of the present invention.
  • FIG. 8 is a schematic diagram of the timing measurement curve of the method of the present invention under a multipath channel and a Gaussian channel when the signal-to-noise ratio is high;
  • Fig. 9 is a schematic diagram of a timing measurement curve of the method of the present invention under a multipath channel at a low signal-to-noise ratio
  • FIG. 10 is a schematic diagram of the principle of adaptive threshold technology in an embodiment of the present invention.
  • FIG. 11 is a schematic diagram of a timing measurement curve in a multipath channel when the signal-to-noise ratio is 10dB after the adaptive threshold technology is introduced in an embodiment of the present invention
  • FIG. 12 is a schematic diagram of a timing measurement curve under a multipath channel when the signal-to-noise ratio is -5dB after the adaptive threshold technology is introduced in an embodiment of the present invention
  • FIG. 13 is a schematic diagram of comparison of timing synchronization mean square error curves of different algorithms in an embodiment of the present invention.
  • the embodiment of the present invention provides a method for synchronizing the symbol timing of the data transmission link in the simultaneous transmission system of the steel penetration data. As shown in FIG. 6, the method includes the following steps:
  • the structure of the training sequence includes symbol differences and conjugate relationships
  • the present invention designs a new training sequence structure in the improved algorithm to improve the timing estimation performance of the algorithm.
  • the designed new training sequence structure introduces symbol differences and conjugate relationships, and enhances the autocorrelation of the training sequence.
  • the structure of the new training sequence is:
  • the total length of the training sequence is N
  • the length L of each sequence symbol is N/4
  • B is conjugate with A
  • -A and -B are negative structures of A and B, respectively.
  • timing measurement calculation is performed by the following formula:
  • d is the first time sample value corresponding to the sliding window
  • r * (d) and r(d) are conjugate each other
  • P g (d) is the value of the related item in the sequence symbol
  • R g (d) is The energy value of the training sequence.
  • the present invention proposes a new timing measurement calculation method for the new training sequence structure, solves the defects of the traditional synchronization timing algorithm, and improves the accuracy of timing synchronization.
  • the simulation results show that in the Gaussian channel and multipath channel with high signal-to-noise ratio, the improved algorithm not only overcomes the ambiguity in timing estimation caused by the phenomenon of Schmidl&D.Cox algorithm platform, but also avoids the low timing synchronization accuracy caused by the multi-peak phenomenon of Minn algorithm.
  • the problem has a good timing effect.
  • the signal transmission channel through steel is a multipath channel, and there may be an environmental condition with low signal-to-noise ratio in the signal transmission system through steel.
  • Figure 9 is a schematic diagram of the timing measurement curve of the improved algorithm under a multipath channel when the signal-to-noise ratio is low. It can be seen from the figure that in the multipath channel with low signal-to-noise ratio, there are many interference peaks in the timing measurement curve of the improved algorithm, and the interference peaks may cause misjudgment in synchronization decision.
  • the method further includes:
  • an adaptive threshold based on the real-time signal power value is used for boundary judgment.
  • the steps for boundary decision include:
  • the scaling factor ⁇ and the fixed threshold value ⁇ can be obtained through previous simulation and engineering experience, and the average power P of the received signal is obtained by smooth filtering.
  • the simulation result is shown in Fig. 12.
  • the timing measurement curve has many high peak points in the multipath channel, so the threshold-based symbol start boundary decision may have a certain deviation.
  • the method of the present invention introduces the relationship between the length of the interval between the two peaks, and according to the judgment condition of whether the interval between the two peaks is 1/2 the length of the synchronization symbol, the starting position of the data symbol can still be accurately determined. Therefore, the method of the present invention still has better timing synchronization performance in a multipath environment with low signal-to-noise ratio after introducing the adaptive threshold technology.
  • the method of the present invention also includes:
  • timing mean square error function MSE Use the timing mean square error function to evaluate the performance of the algorithm.
  • the timing mean square error function MSE is defined as follows:
  • n is the number of simulations
  • observed m represents the m-th observation value
  • set m represents the m-th actual set value
  • the timing mean square error function is an important criterion for evaluating the performance of synchronization algorithms.
  • the present invention simulates the synchronization performance of the Schmidl&D.Cox algorithm, the Minn algorithm and the improved algorithm of the present invention based on the mean square error function, and verifies the synchronization performance of the algorithm under a multipath channel within a certain signal-to-noise ratio range.
  • the relevant parameters are as follows:
  • the number of subcarriers is 256; the signal-to-noise ratio SNR ranges from -5dB to 10dB; the noise type is Gaussian white noise; and the channel is a multipath channel.
  • the specific implementation of the present invention has the following beneficial effects:
  • the present invention solves the platform effect of the Schmidl&D.Cox algorithm by designing a new training sequence structure in the improved algorithm, introducing symbol differences and conjugate relations, and proposing a new timing measurement method. It has the defect of large synchronization error with Minn algorithm; in addition, in view of the low signal-to-noise environment of the steel-piercing signal transmission system, the method of the present invention introduces an adaptive threshold technology based on real-time signal power value, so that the timing synchronization accuracy rate is low. The noise ratio is improved, and the overall performance of the simultaneous transmission system of the number of steel penetration is improved.

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Abstract

本发明提供一种穿钢数能同传系统中数据传输链路符号定时同步的方法，所述方法包括：首先，设计新的训练序列结构来提高算法的定时估计性能，设计的新的训练序列结构中引入了符号差别和共轭关系，增强了训练序列的自相关性；其次，针对本发明设计的训练序列结构提出了新的定时测度计算方法，解决了传统同步定时算法的缺陷，提升了定时同步的准确率；最后，本发明方法还引入基于实时信号功率值的自适应门限技术，在穿钢信号传输系统中出现信噪比较低的情况下使符号定时同步效果得到改善。本发明能够提升符号定时同步的准确率，进而改善穿钢数能同传系统的整体性能。

Description

穿钢数能同传系统中数据传输链路符号定时同步的方法 技术领域
本发明涉及超声波通信技术领域，特别涉及一种穿钢数能同传系统中数据传输链路符号定时同步的方法。
背景技术
在工业领域经常需要对密闭容器进行通信和监测，比如潜水艇舱体内外信息传递、管道压力监测等，因此需要有可靠稳定的通信要求。
根据现有的通信方式，若使用有线传输技术需要在容器壁或舱壁上穿孔，该方法除费用高昂以外，还会破坏容器或舱壁的完整结构。另外，由于金属密闭容器具有电磁屏蔽效应，电磁波无法穿透金属壁进行有效的信号传输。
超声波因其方向性好、穿透力强的特性，在金属中传输时具备衰减小、速度快的特点。因此可以用超声波作为信息传输的载体，金属信道作为信息传输的媒介，实现金属容器内外数据的传输。
穿钢信号传输系统是针对传统通信方式无法在金属厚壁中传输的问题而建立的系统，突破了有线传输通信和传统射频通信的瓶颈，能够广泛应用于工业领域。
如图1所示为超声波穿金属板通信示意图，此系统包括：发射换能器1、耦合剂2、金属壁3、接收换能器4。金属壁3左侧的发射换能器1将电信号转换为超声波信号，超声波信号穿过金属壁3到达接收端的接收换能器4，接收换能器4将超声波信号还原为电信号。发射换能器1与接收换能器4对称放置在金属壁3的两侧，换能器与金属壁3之间通过耦合剂2相连。
如图2所示为OFDM系统基本架构示意图。发送端的DSP模块包含了符号调制、傅里叶反变换、插入循环前缀、上变频过程。输入信号经过发送端DSP后经过DAC模块得到模拟信号，模拟信号通过发射换能器转换为超声波信号穿过金属壁。
接收端的DSP模块包含了符号解调、傅里叶变换、去除循环前缀、下变频和信号同步过程。穿过金属壁后的超声波信号经过另一侧的接收换能器重新转换为电信号，电信号经过峰均功率比抑制模块之后通过低噪声放大器，再经由接收端DSP得到输出信号。
OFDM具有频谱利用率高、实现简单以及有效抵抗信号传输过程中的频率选择性衰落和多径效应等优点。
OFDM中的各个载波是相互正交的，每个载波在一个符号时间内有整数个载波周期，每个载波的频谱零点和相邻载波的零点重叠，这样便减小了载波间的干扰。由于载波间有部分重叠，提高了频带利用率。OFDM系统中正交的子载波可以利用快速傅利叶变换实现调制和解调。
在OFDM系统的发射端加入保护间隔，主要是为了消除多径所造成的符号间干扰。其方法是在OFDM符号保护间隔内填入循环前缀，这样时延小于保护间隔的信号就不会在解调过程中产生符号间干扰。
在穿钢数能同传系统中，不同同步方式对系统的影响不尽相同，本发明主要解决符号定时偏差问题。多径效应导致信号在金属壁中传输的距离不同，接收端需要准确地判断信号的起始时刻来解调信号。依据OFDM符号首部起点预测位置的不同，符号定时偏差对系统性能的影响则不尽相同。如图3所示为OFDM定时同步结果的3种情形示意图，展示了符号定时偏差可能出现的几种情况。
情形1：定时准确，此情况下预测的OFDM符号起始点和精确位置一致。可以完全恢复OFDM符号且不会引入干扰。
情形2：定时超前，此情况下预测的OFDM符号起始点比精确位置略早。由于循环前缀是由同步符号末尾部分复制而来，因此，FFT窗口仍然可以包含完整的符号信息。
情形3：定时滞后，此情况下预测的OFDM符号起始点比精确位置略晚。接收端FFT窗口将会覆盖当前OFDM符号数据的一部分以及下一个OFDM符号循环前缀或数据的一部分。这时，数据信息的一部分就会丢失，最为严重的是子载波间的正交性遭到破坏，进而在系统中引入符号间干扰和载波间干扰。
由上述分析可知，在穿钢数能同传系统数据链路中对符号定时同步进行研 究具有重要意义，其直接决定着整个系统的数据传输性能。
如图4所示为传统符号定时同步Schmidl&D.Cox算法度量函数曲线示意图。1997年，Schmidl与D.Cox等设计了一种前半部分和后半部分完全相同的训练序列，结合相关运算完成OFDM的符号同步。
Schmidl&D.Cox算法的序列结构为：
S SC＝[A A]
Schmidl&D.Cox算法的定时度量函数为：
Figure PCTCN2020101050-appb-000001
Figure PCTCN2020101050-appb-000002
Figure PCTCN2020101050-appb-000003
上述式中，d为滑动窗口对应的第一个时间样值，训练序列的总长度为N，序列符号的长度L均为N/2，接收信号为r(d)，r *(d)和r(d)互为共轭，P sc(d)为相关求和公式，R sc(d)为后半部分序列的能量值。
对Schmidl&D.Cox算法进行仿真，仿真结果如图4所示，相关参数如下：子载波数为256；信噪比SNR＝10dB；所述信道为高斯信道。
Schmidl&D.Cox算法存在“峰值平台”的问题，具有定时估计模糊的缺陷。
如图5所示为另一传统符号定时同步Minn算法度量函数曲线示意图。2000年，Minn等人针对Schmidl&D.Cox算法中存在的“峰值平台”问题，改进了训练序列的结构。
Minn算法的序列结构为：
S m＝[B B -B -B]
Minn算法的定时度量函数为：
Figure PCTCN2020101050-appb-000004
Figure PCTCN2020101050-appb-000005
Figure PCTCN2020101050-appb-000006
上述式中，d为滑动窗口对应的第一个时间样值，训练序列的总长度为N，序列符号的长度L均为N/4，-B为B的负值结构。P m(d)为序列符号中相关项的值，当k＝0时，计算前两段序列的相关性，当k＝1时，计算后两段序列的相关性，R m(d)为训练序列的能量值，用于对符号定时度量的归一化。
对Minn算法进行仿真，仿真结果如图5所示，相关参数如下：子载波个数为256；信噪比SNR＝10dB；所述信道为高斯信道。
然而，Minn算法的多峰现象造成定时同步准确率较低。
发明内容
本发明的目的在于提供一种穿钢数能同传系统中数据传输链路符号定时同步的方法，主要是解决符号定时问题，从而提升穿钢数能同传系统的整体性能。
为解决上述技术问题，本发明的实施例提供一种穿钢数能同传系统中数据传输链路符号定时同步的方法，包括以下步骤：
生成训练序列，所述训练序列的结构中包括符号差别和共轭关系；
根据所述训练序列进行定时测度计算。
优选地，所述训练序列的结构为：
S g＝[A -B -A B]
其中，所述训练序列的总长度为N，每个序列符号的长度L均为N/4，B与A共轭，-A和-B分别为A和B的负值结构。
优选地，通过以下公式进行定时测度计算：
Figure PCTCN2020101050-appb-000007
Figure PCTCN2020101050-appb-000008
其中，d为滑动窗口对应的第一个时间样值，r *(d)和r(d)互为共轭，P g(d)为序列符号中相关项的值，R g(d)为所述训练序列的能量值。
优选地，所述方法还包括：
当系统的信噪比低于预设值时，利用基于实时信号功率值的自适应门限进行边界判决。
优选地，进行边界判决的步骤包括：
计算相关度量值M和自适应阈值V，其中V＝αP+β，α为缩放系数，β为固定门限阈值，P为接收信号的平均功率；
判断是否检测到峰值点，若M＞V，则认为检测到峰值点，进入下一步；
进行峰值点记录，记录所有大于自适应阈值的峰值点；
进行边界判决，从首个峰值点开始，对每个峰值点做时序判断，判断是否存在与当前峰值点间隔为1/2个序列符号长度的峰值点，若存在，则当前峰值点对应的采样点为数据的起始边界，否则返回第一步。
优选地，所述方法还包括：
利用定时均方误差函数评价算法性能，定时均方误差函数MSE的定义如下：
Figure PCTCN2020101050-appb-000009
其中，n为仿真次数，observed m表示第m次的观测值，set m表示第m次实际设定值。
本发明的上述技术方案的有益效果如下：
本发明设计了新的训练序列结构并提出新的定时测度计算方法，解决了Schmidl&D.Cox算法的平台效应和Minn算法同步误差较大的缺陷，提升了定时同步的准确率，改善了穿钢数能同传系统中数据链路的符号定时同步问题，进而改善穿钢数能同传系统的整体性能。
附图说明
图1是超声波穿金属板通信示意图；
图2是OFDM系统基本架构示意图；
图3是OFDM定时同步结果的三种情形示意图；
图4是Schmidl&D.Cox算法度量函数曲线示意图；
图5是Minn算法的度量函数曲线示意图；
图6是本发明实施例提供的用于穿钢数能同传系统中数据传输链路符号定时同步的方法的流程图；
图7是本发明实施例中的训练序列的同步符号结构示意图；
图8是高信噪比时多径信道与高斯信道下本发明方法的定时度量曲线示意图；
图9是低信噪比时多径信道下本发明方法的定时度量曲线示意图；
图10是本发明实施例中自适应门限技术的原理示意图；
图11是本发明实施例中引入自适应门限技术后的信噪比为10dB时多径信道下定时度量曲线示意图；
图12是本发明实施例中引入自适应门限技术后的信噪比为-5dB时多径信道下定时度量曲线示意图；
图13是本发明实施例中不同算法的定时同步均方误差曲线对比示意图。
具体实施方式
为使本发明要解决的技术问题、技术方案和优点更加清楚，下面将结合附图及具体实施例进行详细描述。
本发明的实施例提供了一种穿钢数能同传系统中数据传输链路符号定时同步的方法，如图6所示，该方法包括以下步骤：
生成训练序列，所述训练序列的结构中包括符号差别和共轭关系；
根据所述训练序列进行定时测度计算。
本发明在改进算法中设计新的训练序列结构来提高算法的定时估计性能，设计的新训练序列的结构中引入了符号差别和共轭关系，增强了训练序列的自 相关性。
进一步地，如图7所示，新的训练序列的结构为：
S g＝[A -B -A B]
其中，训练序列的总长度为N，每个序列符号的长度L均为N/4，B与A共轭，-A和-B分别为A和B的负值结构。
进一步地，通过以下公式进行定时测度计算：
Figure PCTCN2020101050-appb-000010
Figure PCTCN2020101050-appb-000011
其中，d为滑动窗口对应的第一个时间样值，r *(d)和r(d)互为共轭，P g(d)为序列符号中相关项的值，R g(d)为所述训练序列的能量值。
本发明针对新的训练序列结构提出了新的定时测度计算方法，解决了传统同步定时算法的缺陷，提升了定时同步的准确率。
对本发明方法进行仿真，仿真结果如图8所示，相关参数如下：
子载波数为256；信噪比SNR＝10dB；噪声类型为高斯白噪声；延时为34个采样点；所述信道为高斯信道和多径信道。
仿真结果说明在高信噪比的高斯信道和多径信道下，改进算法既克服了Schmidl&D.Cox算法平台现象导致的定时估计模糊缺陷，又避免了Minn算法多峰现象造成的定时同步准确率低的问题，具有较好的定时效果。
穿钢信号传输信道为多径信道，穿钢信号传输系统中可能会存在信噪比较低的环境状况。
进一步地，在多径信道下验证算法的准确性。相关参数如下：
子载波数256；信噪比SNR＝-5dB；噪声类型为高斯白噪声；延时为34个采样点，所述信道为多径信道。
在低信噪比环境下，同步序列的相关性会受到较大的破坏，进而降低本发明方法的同步性能。如图9所示为低信噪比时在多径信道下改进算法的定时度量曲线示意图。从图中可以得知，在低信噪比的多径信道下，改进算法的定时度量曲线出现了许多干扰峰值，干扰峰值可能会导致同步判决时的误判。
为了解决上述问题，提高本发明方法在低信噪比环境下的同步性能，进一步地，所述方法还包括：
当系统的信噪比低于预设值时，利用基于实时信号功率值的自适应门限进行边界判决。
具体地，参考图10，进行边界判决的步骤包括：
计算相关度量值M和自适应阈值V，其中V＝αP+β，α为缩放系数，β为固定门限阈值，P为接收信号的平均功率；
判断是否检测到峰值点，若M＞V，则认为检测到峰值点，进入下一步；
进行峰值点记录，记录所有大于自适应阈值的峰值点；
进行边界判决，从首个峰值点开始，对每个峰值点做时序判断，判断是否存在与当前峰值点间隔为1/2个序列符号长度的峰值点，若存在，则当前峰值点对应的采样点为数据的起始边界，否则返回第一步。
其中，缩放系数α和固定门限阈值β可以通过前期的仿真和工程经验得到，接收信号的平均功率P使用平滑滤波的方式得到。
在高信噪比环境时，验证多径信道下算法的同步性能，相关参数如下：
子载波数256；信噪比SNR＝10dB；噪声类型为高斯白噪声；延时为34个采样点；所述信道为多径信道。
仿真结果如图11所示，定时度量曲线中出现了两个明显峰值，且第一个峰值出现在准确定时点(第34个采样点)处，观察两个峰值间的间隔，满足间隔差为1/2个同步符号长度(128个采样点)的时序关系。因此，本发明方法引入自适应门限技术后在信噪比较好的多径环境下有着较好的定时同步效果。
进一步地，在低信噪比环境时，验证多径信道下算法的同步性能，相关参 数如下：
子载波数256；信噪比SNR＝-5dB；噪声类型为高斯白噪声；延时为34个采样点；所述信道为多径信道。
仿真结果如图12所示，在低信噪比环境下，定时度量曲线在多径信道中出现了很多高峰值点，因此基于阈值的符号起始边界判决可能会出现一定的偏差。本发明方法引入了两峰值间的间隔长度关系，依据两峰值之间的间隔是否为1/2个同步符号长度这一判决条件，仍然可以准确地判断出数据符号的起始位置。因此，本发明方法引入自适应门限技术后在信噪比较低的多径环境下仍然有着较好的定时同步性能。
进一步地，本发明方法还包括：
利用定时均方误差函数评价算法性能，定时均方误差函数MSE的定义如下：
Figure PCTCN2020101050-appb-000012
其中，n为仿真次数，observed m表示第m次的观测值，set m表示第m次实际设定值。
定时均方误差函数是评价同步算法性能的重要标准。本发明基于均方误差函数对Schmidl&D.Cox算法、Minn算法以及本发明改进算法的同步性能进行仿真，在一定信噪比范围内验证多径信道下算法的同步性能，相关参数如下：
子载波数256；信噪比SNR范围为-5dB到10dB；噪声类型为高斯白噪声；所述信道为多径信道。
仿真结果如图13所示。由图可知，Schmidl&D.Cox算法在不同信噪比环境下的定时均方误差明显比其他算法大，其定时同步性能较差。在低信噪比的环境下，本发明方法的定时同步准确率和稳定性均优于其他算法。
本发明的具体实施方式具有以下有益效果：本发明通过在改进算法中设计新的训练序列结构，引入符号差别和共轭关系，并提出新的定时测度方法，解决了Schmidl&D.Cox算法的平台效应和Minn算法同步误差较大的缺陷；另外，针对穿钢信号传输系统存在信噪比较低的环境，本发明方法引入基于实时信号功率值的自适应门限技术，使定时同步准确率在低信噪比条件下得到改善，进 而提升穿钢数能同传系统的整体性能。
以上所述是本发明的优选实施方式，应当指出，对于本技术领域的普通技术人员来说，在不脱离本发明所述原理的前提下，还可以做出若干改进和润饰，这些改进和润饰也应视为本发明的保护范围。

Claims (6)

  1. 一种穿钢数能同传系统中数据传输链路符号定时同步的方法，其特征在于，包括以下步骤：
    生成训练序列，所述训练序列的结构中包括符号差别和共轭关系；
    根据所述训练序列进行定时测度计算。
  2. 根据权利要求1所述的穿钢数能同传系统中数据传输链路符号定时同步的方法，其特征在于，所述训练序列的结构为：
    S g＝[A -B -A B]
    其中，所述训练序列的总长度为N，每个序列符号的长度L均为N/4，B与A共轭，-A和-B分别为A和B的负值结构。
  3. 根据权利要求2所述的穿钢数能同传系统中数据传输链路符号定时同步的方法，其特征在于，通过以下公式进行定时测度计算：
    Figure PCTCN2020101050-appb-100001
    Figure PCTCN2020101050-appb-100002
    其中，d为滑动窗口对应的第一个时间样值，r *(d)和r(d)互为共轭，P g(d)为序列符号中相关项的值，R g(d)为所述训练序列的能量值。
  4. 根据权利要求1-3中任一项所述的穿钢数能同传系统中数据传输链路符号定时同步的方法，其特征在于，所述方法还包括：
    当系统的信噪比低于预设值时，利用基于实时信号功率值的自适应门限进行边界判决。
  5. 根据权利要求4所述的穿钢数能同传系统中数据传输链路符号定时同步的方法，其特征在于，进行边界判决的步骤包括：
    计算相关度量值M和自适应阈值V，其中V＝αP+β，α为缩放系数，β为固定门限阈值，P为接收信号的平均功率；
    判断是否检测到峰值点，若M＞V，则认为检测到峰值点，进入下一步；
    进行峰值点记录，记录所有大于自适应阈值的峰值点；
    进行边界判决，从首个峰值点开始，对每个峰值点做时序判断，判断是否存在与当前峰值点间隔为1/2个序列符号长度的峰值点，若存在，则当前峰值点对应的采样点为数据的起始边界，否则返回第一步。
  6. 根据权利要求1-3中任一项所述的穿钢数能同传系统中数据传输链路符号定时同步的方法，其特征在于，所述方法还包括：
    利用定时均方误差函数评价算法性能，定时均方误差函数MSE的定义如下：
    Figure PCTCN2020101050-appb-100003
    其中，n为仿真次数，observed m表示第m次的观测值，set m表示第m次实际设定值。
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