CN113315733B - A time-frequency synchronization method, communication system and storage medium - Google Patents

Abstract

The invention discloses a time-frequency synchronization method, a communication system and a medium. The method includes: a signal transmitting device obtains a synchronization sequence; the synchronization sequence is composed of a plurality of identical sequence units, and the sequence units are composed of parallel information symbols; Copy the synchronization sequence according to the number of frequency factors, and multiply the copied synchronization sequence by the spreading factor to obtain the spread spectrum sequence; perform inverse Fourier transform on the spread spectrum sequence to obtain the time domain sequence of the synchronization sequence, and convert the time domain sequence to the time domain sequence. The sequence is sent to the signal receiving device, so that the signal receiving device despreads the time domain sequence to obtain the synchronization sequence, and uses the sequence units in the synchronization sequence to perform time-frequency synchronization. The invention uses a synchronization sequence composed of multiple identical sequence units to perform time-frequency synchronization, so as to ensure that the synchronization sequence contains the repetitive structure required for time-frequency synchronization; The synchronization sequence is recovered by despreading the spreading sequence.

Description

A time-frequency synchronization method, communication system and storage medium

technical field

The present invention relates to the field of mobile communication systems, in particular to a time-frequency synchronization method, a communication system and a storage medium.

Background technique

The multi-carrier spread spectrum system is improved from the existing OFDM system, and the original OFDM symbol sequence can be spread spectrum gain to achieve the effect of improving the sensitivity of the OFDM receiver. In the communication link of the multi-carrier spread spectrum system, time-frequency synchronization is an important link. However, the multi-carrier spread spectrum system performs the spread spectrum operation on the parallel information symbol sequence in the signal transmission, so that the signal bandwidth obtained after despreading varies with the spread spectrum factor, which cannot be performed by the existing time-frequency synchronization method. Therefore, it is necessary to redesign the time-frequency synchronization method of the multi-carrier spread spectrum system.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a time-frequency synchronization method, a communication system and a storage medium, which can perform time-frequency synchronization by using a synchronization sequence including a repeating structure required for time-frequency synchronization, and simultaneously perform spread spectrum processing on the synchronization sequence, and further Make sure that the signal receiving device can despread the spreading sequence to restore the synchronization sequence.

In order to solve the above-mentioned technical problems, the present invention provides a time-frequency synchronization method, comprising:

，且所述并行信息符号的信号值同时存在零和非零值时，所述同步序列为短同步序列；The signal transmitting device obtains a synchronization sequence; the synchronization sequence is composed of a plurality of identical sequence units, and the sequence units are composed of parallel information symbols; when the number of parallel information symbols in the sequence unit is 1, and the parallel information symbols When the value of the signal is not zero, the synchronization sequence is a long synchronization sequence; when the number of parallel information symbols in the sequence unit is

, and when the signal value of the parallel information symbol has both zero and non-zero values, the synchronization sequence is a short synchronization sequence;

Duplicating the synchronization sequence according to a preset number of spreading factors, and multiplying the copied synchronization sequence by the spreading factor to obtain a spreading sequence;

Perform an inverse Fourier transform on the spread spectrum sequence to obtain a time domain sequence of the synchronization sequence, and send the time domain sequence to a signal receiving device, so that the signal receiving device can perform an inverse Fourier transform on the time domain sequence. The synchronization sequence is obtained by despreading, and time-frequency synchronization is performed using the sequence elements in the synchronization sequence.

Optionally, the acquiring synchronization sequence includes:

obtaining the long synchronization sequence and the short synchronization sequence;

Correspondingly, duplicating the synchronization sequence according to the preset number of spreading factors, and multiplying the copied synchronization sequence by the spreading factor to obtain a spreading sequence, including:

Replicate the long synchronization sequence and the short synchronization sequence according to the preset number of spreading factors, and multiply the replicated long synchronization sequence and the replicated short synchronization sequence by the spreading factor respectively to obtain the long spreading factor. frequency sequences and short spreading sequences;

Correspondingly, performing an inverse Fourier transform on the spread spectrum sequence to obtain a time-domain sequence of the synchronization sequence, and sending the time-domain sequence to a signal receiving device, includes:

performing the inverse Fourier transform on the long spreading sequence and the short spreading sequence to obtain a long time domain sequence and a short time domain sequence;

splicing the long time domain sequence and the short time domain sequence so that the short time domain sequence is located in the front of the long time domain sequence to obtain a total time domain sequence, and sending the total time domain sequence to the signal receiving device.

Optionally, the signal receiving device performs despreading processing on the time domain sequence to obtain the synchronization sequence, and performs time-frequency synchronization by using sequence elements in the synchronization sequence, including:

The signal receiving device performs the despreading process on the received time domain sequence by using the spreading factor to obtain the synchronization sequence;

Time-frequency synchronization is performed on the sequence units in the synchronization sequence by using the symbol timing estimation method and the frequency offset estimation method.

Optionally, performing time-frequency synchronization on sequence units in the synchronization sequence by using a symbol timing estimation method and a frequency offset estimation method includes:

Fourier transform is performed on the synchronization sequence, and the value of each parallel information symbol included in the transformed synchronization sequence is used to determine the type of the synchronization sequence;

When the type of the synchronization sequence is the short synchronization sequence, use the symbol timing estimation method and the frequency offset estimation method to perform first time-frequency synchronization on the sequence elements in the synchronization sequence, and determine the initial frequency offset estimation scope;

When the type of the synchronization sequence is the long synchronization sequence and the initial frequency offset estimation range is determined, within the initial frequency offset range, use the symbol timing estimation method and the frequency offset estimation method to The sequence units in the synchronization sequence perform second time-frequency synchronization to determine the final frequency offset estimation range.

The present invention also provides a communication system, comprising: a signal transmitting device and a signal receiving device, wherein,

，且所述并行信息符号的信号值同时存在零和非零值时，所述同步序列为短同步序列；依照预设的扩频因子的数量复制所述同步序列，并将复制后的同步序列与所述扩频因子相乘，得到扩频序列；将所述扩频序列进行反向傅里叶变换得到所述同步序列的时域序列，并将所述时域序列发送至所述信号接收设备；The signal transmitting device is used to obtain a synchronization sequence; the synchronization sequence is composed of a plurality of identical sequence units, and the sequence units are composed of parallel information symbols; when the number of parallel information symbols in the sequence unit is 1, and When the signal value of the parallel information symbol is not zero, the synchronization sequence is a long synchronization sequence; when the number of parallel information symbols in the sequence unit is

, and when the signal value of the parallel information symbol has both zero and non-zero values, the synchronization sequence is a short synchronization sequence; the synchronization sequence is copied according to the preset number of spreading factors, and the copied synchronization sequence Multiply with the spreading factor to obtain a spreading sequence; perform an inverse Fourier transform on the spreading sequence to obtain a time domain sequence of the synchronization sequence, and send the time domain sequence to the signal receiver equipment;

The signal receiving device is configured to perform despreading processing on the time domain sequence to obtain the synchronization sequence, and perform time-frequency synchronization by using sequence units in the synchronization sequence.

Optionally, the signal transmitting device is further configured to acquire a long synchronization sequence and a short synchronization sequence; copy the long synchronization sequence and the short synchronization sequence according to the preset number of spreading factors, and respectively copy the copied long synchronization sequence and the short synchronization sequence. Multiplying the long synchronization sequence and the replicated short synchronization sequence with the spreading factor to obtain a long spreading sequence and a short spreading sequence; performing an inverse Fourier transformation on the long spreading sequence and the short spreading sequence transform to obtain a long time domain sequence and a short time domain sequence; splicing the long time domain sequence and the short time domain sequence, so that the short time domain sequence is located in the front of the long time domain sequence, to obtain a total time-domain sequence, and sending the total time-domain sequence to the signal receiving device.

Optionally, the signal receiving device is further configured to perform the despreading process on the received time domain sequence by using the spreading factor to obtain a synchronization sequence; The sequence units in the synchronization sequence perform the time-frequency synchronization.

The present invention also provides a storage medium, where computer-executable instructions are stored in the storage medium, and when the computer-executable instructions are loaded and executed by a processor, the above-mentioned time-frequency synchronization method is implemented.

，且所述并行信息符号的信号值同时存在零和非零值时，所述同步序列为短同步序列。The present invention provides a time-frequency synchronization method, including: a signal transmitting device obtains a synchronization sequence; the synchronization sequence is composed of a plurality of identical sequence units, and the sequence units are composed of parallel information symbols; Quantitatively copy the synchronization sequence, and multiply the copied synchronization sequence by the spreading factor to obtain a spread spectrum sequence; perform an inverse Fourier transform on the spread spectrum sequence to obtain a time domain sequence of the synchronization sequence , and send the time domain sequence to the signal receiving device, so that the signal receiving device despreads the time domain sequence to obtain the synchronization sequence, and uses the sequence elements in the synchronization sequence to perform time-frequency synchronization; wherein, when the number of parallel information symbols in the sequence unit is 1, and the signal value of the parallel information symbols is not zero, the synchronization sequence is a long synchronization sequence; when the parallel information symbols in the sequence unit are The number of symbols is

, and when the signal values of the parallel information symbols have both zero and non-zero values, the synchronization sequence is a short synchronization sequence.

It can be seen that the signal transmitting device in the present invention replicates the synchronization sequence according to the number of spreading factors, and multiplies the replicated synchronization sequence by the spreading factor to obtain the spreading sequence. In other words, the signal in the present invention The transmitting device also performs spread spectrum processing on the synchronization sequence, and uses the spread spectrum obtained by the spread spectrum for subsequent data conversion and data transmission, which ensures that the signal receiving device can despread the spread spectrum sequence to restore the synchronization sequence; at the same time, The synchronization sequence used in the present invention is composed of a plurality of identical sequence units, which can ensure that the synchronization sequence contains a specific repetitive structure, and can flexibly adjust the parallel information symbols in the synchronization sequence to obtain long synchronization sequences and short synchronization sequences. , not only can ensure that the signal receiving equipment can use the related method of time-frequency synchronization to synchronize the synchronization sequence, ensure that the multi-carrier spread spectrum system can perform time-frequency synchronization normally, and can also use different types of synchronization sequences to perform time-frequency synchronization with different precisions. Time-frequency synchronization improves the flexibility of time-frequency synchronization. The present invention also provides a communication system and a storage medium, which have the above beneficial effects.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to the provided drawings without creative work.

1 is a flowchart of a time-frequency synchronization method provided by an embodiment of the present invention;

2 is a schematic diagram of generating a time-domain sequence by using a synchronization sequence according to an embodiment of the present invention;

3 is a schematic diagram of a transmitter of a multi-carrier spread spectrum system according to an embodiment of the present invention;

4 is a schematic diagram of a receiving end of a multi-carrier spread spectrum system according to an embodiment of the present invention;

5 is a schematic diagram of a classic delay correlation synchronization algorithm provided by an embodiment of the present invention;

6 is a schematic diagram of an IFFT property corresponding to a short synchronization sequence provided by an embodiment of the present invention;

FIG. 7 is another schematic diagram of generating a time-domain sequence by using a synchronization sequence according to an embodiment of the present invention;

FIG. 8 is another schematic diagram of generating a time-domain sequence by using a synchronization sequence according to an embodiment of the present invention;

9 is a schematic diagram of a synchronization sequence based on a short and long repetition structure provided by an embodiment of the present invention;

FIG. 10 is a structural block diagram of a communication system according to an embodiment of the present invention.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, but not all embodiments. 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.

The multi-carrier spread spectrum system is improved from the existing OFDM system, and the original OFDM symbol sequence can be spread spectrum gain to achieve the effect of improving the sensitivity of the OFDM receiver. In the communication link of the multi-carrier spread spectrum system, time-frequency synchronization is an important link. However, the multi-carrier spread spectrum system performs the spread spectrum operation on the parallel information symbol sequence in the signal transmission, so that the signal bandwidth obtained after despreading varies with the spread spectrum factor, which cannot be performed by the existing time-frequency synchronization method. Therefore, it is necessary to redesign the time-frequency synchronization method of the multi-carrier spread spectrum system. In view of this, the present invention provides a time-frequency synchronization method, which can perform time-frequency synchronization by using a synchronization sequence including a repetitive structure required for time-frequency synchronization, and also performs spectrum spread processing on the synchronization sequence, thereby ensuring that the signal receiving device can The synchronization sequence is recovered by despreading the spreading sequence. Please refer to FIG. 1. FIG. 1 is a flowchart of a time-frequency synchronization method provided by an embodiment of the present invention. The method may include:

，且并行信息符号的信号值同时存在零和非零值时，同步序列为短同步序列。S101. The signal transmitting device acquires a synchronization sequence; the synchronization sequence is composed of multiple identical sequence units, and the sequence units are composed of parallel information symbols; when the number of parallel information symbols in the sequence unit is 1, and the signal value of the parallel information symbols is not zero When , the synchronization sequence is a long synchronization sequence; when the number of parallel information symbols in the sequence unit is

, and the signal values of the parallel information symbols have both zero and non-zero values, the synchronization sequence is a short synchronization sequence.

，其中

表示幂。需要说明的是，本发明实施例并不限定

的具体取值，可根据实际应用需求进行调整。进一步，本发明实施例并不限定每一序列单元可包含的并行信息符号的通路数量，同样可根据实际应用需求进行调整。可以理解的是，当总通路数量K的取值为2的幂次时，每一序列单元可包含的并行信息符号的通路数量也可以为2的幂次，只要该通路数量能够整除总通路数量K即可；同样可以理解的是，通路数量除以总通路数量K得到的除数便是序列单元的数量。进一步，本发明实施例也不限定每个序列单元所包含的并行信息符号的信号值，该信号值既可以为零，也可以为非零值；当然，若每个序列单元仅包含一个并行信息符号时，为了确保时频同步有效，该并行信息符号的信号值需要为非零值。In the embodiment of the present invention, a synchronization sequence composed of multiple identical sequence units is used for time-frequency synchronization, which can ensure that the synchronization sequence has multiple repeated specific structures, and can be used for time-frequency synchronization. The sequence unit used in the present invention is composed of parallel information symbols. Since the sequence units are all the same, in other words, the number of parallel information symbols contained in each sequence unit is the same, and the signal values of the corresponding parallel information symbols between the sequence units are the same. Also the same. The embodiments of the present invention do not limit the generation method of parallel information symbols, and reference may be made to the related technology of OFDM (Orthogonal Frequency Division Multiplexing, orthogonal frequency division multiplexing technology). For example, parallel information symbols can be obtained by serial-parallel transformation of information symbols. It can be understood that the parallel information symbols have a parallel structure (ie, a multi-channel structure). The embodiment of the present invention does not limit the total number of channels K of all parallel information symbols in the synchronization signal, which can be adjusted according to actual application requirements. In order to facilitate bisection, the value of K can be set to a power of 2, that is,

,in

represents a power. It should be noted that the embodiments of the present invention are not limited

The specific value of , can be adjusted according to actual application requirements. Further, the embodiment of the present invention does not limit the number of channels of parallel information symbols that can be included in each sequence unit, and can also be adjusted according to actual application requirements. It can be understood that when the value of the total number of channels K is a power of 2, the number of channels of parallel information symbols that each sequence unit can contain can also be a power of 2, as long as the number of channels can divide the total number of channels. K is sufficient; it is also understandable that the divisor obtained by dividing the number of channels by the total number of channels K is the number of sequence units. Further, the embodiment of the present invention also does not limit the signal value of the parallel information symbol included in each sequence unit, and the signal value may be either zero or a non-zero value; of course, if each sequence unit contains only one parallel information symbol In order to ensure effective time-frequency synchronization, the signal value of the parallel information symbol needs to be a non-zero value.

Further, because the shorter the synchronization sequence, the larger the estimation range, but the lower the estimation accuracy, and the longer the synchronization sequence, the higher the estimation accuracy, but the smaller the estimation range, in order to further improve the efficiency of time domain synchronization, meet different accuracy requirements For time-frequency synchronization requirements, the structure of the sequence unit in the synchronization sequence can be further improved to use synchronization sequences of different lengths to perform time domain synchronization with different precisions.

In a possible situation, when the number of parallel information symbols in the sequence unit is 1, and the signal value of the parallel information symbols is not zero, the synchronization sequence is a long synchronization sequence.

In the situation shown in Figure 2, since the signal values of the parallel information symbols in the synchronization sequence are not zero (all parallel information symbols in the figure are all white), in this case, the minimum repetitive structure in the synchronization sequence is is the parallel information symbol itself. Since the length of the time domain sequence formed by the synchronization sequence is the length of one OFDM symbol, the sequence length is long and the range of frequency offset estimation is only the frequency offset estimation range of 0.5 subcarriers, so this synchronization sequence is set as a long synchronization sequence.

，且并行信息符号的信号值同时存在零和非零值时，同步序列为短同步序列。In another possible case, when the number of parallel information symbols contained in the sequence unit is

, and the signal values of the parallel information symbols have both zero and non-zero values, the synchronization sequence is a short synchronization sequence.

，

，则其对应的傅里叶变换为：Assuming a discrete sequence of numbers

,

, then its corresponding Fourier transform is:

表示偶数序列对应的傅立叶变换，

表示奇数序列对应的傅立叶变换，

表示傅立叶变换因子。在此基础上，假设

具有以下特性，即其奇数序号

，

所对应的

有值，而偶数序号

，

所对应的

取值为0。则根据上述傅里叶变换所示性质，可以得到：in,

represents the Fourier transform corresponding to the even sequence,

represents the Fourier transform corresponding to the odd sequence,

represents the Fourier transform factor. On this basis, it is assumed that

has the characteristic that its odd ordinal number

,

corresponding to

has value, and even ordinal number

,

corresponding to

The value is 0. Then according to the properties shown by the above Fourier transform, we can get:

At the same time you can get:

Therefore, if the sequence unit in the synchronization sequence is set to contain two parallel information symbols, and the parallel information symbols of odd numbers have a non-zero signal value, while the parallel information symbols of even numbers have a signal value of zero, the length of the synchronization sequence can be defined as Shortened to 0.5 OFDM symbol length. Based on the above characteristics, after the signal transmitting device performs IFFT (Inverse Fast Fourier Transform, inverse Fourier Transform) transformation on the synchronization sequence, the synchronization sequence can have the IFFT property as shown in FIG. 6 . Since the length of the synchronization sequence is only 0.5 OFDM symbol length, and the frequency offset estimation range is the frequency offset estimation range of 1 subcarrier, the above synchronization sequence can be set as a short synchronization sequence. The specific setting process is shown in Figure 7. 7 is another schematic diagram of generating a time domain sequence by using a synchronization sequence according to an embodiment of the present invention. It is precisely because the short synchronization sequence has the above-mentioned properties that the signal receiving device can perform Fourier transform on the received synchronization sequence, thereby determining the type of the synchronization sequence.

Further, the short synchronization sequence can also have other forms. For example, the sequence unit in the synchronization sequence is set to include two parallel information symbols, wherein the parallel information symbols of even serial numbers have a non-zero signal value, and the parallel information symbols of odd serial numbers have a signal value of Zero; of course, a sequence unit may also contain multiple parallel information symbols. When the number of parallel information symbol channels in the sequence unit is a power of 2, a sequence unit with a length of 4 or 8 can also be constructed, and the values of the parallel information symbols in the sequence unit are set to have both zero and non-zero values, so as to further Reduce the length of the sync sequence. As shown in Figure 8, a sequence unit with a length of 4 can be set, and the signal value of the first parallel information symbol in the unit is set to a non-zero value, and the signal values of other parallel information symbols are set to 0. A synchronization sequence with a length of 0.25 OFDM symbols can be obtained.

Further, it should be noted that the embodiment of the present invention does not limit the synchronization sequence to be a long synchronization sequence, a short synchronization sequence, or a combination of a long synchronization sequence and a short synchronization sequence, which can be set according to actual application requirements. Since the long synchronization sequence and the short synchronization sequence correspond to frequency offset estimation ranges of different precisions, the combination of the two can achieve the application effect of rough estimation first and then accurate estimation, which can improve the efficiency of time-frequency synchronization. Therefore, in the embodiment of the present invention , the synchronization sequence can be a combination of a long synchronization sequence and a short synchronization sequence.

S102 , copy the synchronization sequence according to the preset number of spreading factors, and multiply the copied synchronization sequence by the spreading factor to obtain a spreading sequence.

It should be noted that, the embodiment of the present invention does not limit the specific spreading factor, and for details, reference may be made to the related technology of multi-carrier spreading. The embodiment of the present invention also does not limit the specific quantity of the spreading factor, which can be adjusted according to actual application requirements. It should be noted that the product of the number of spreading factors and the total number of channels of parallel information symbols in the synchronization sequence should be equal to the length of one OFDM symbol.

S103: Perform inverse Fourier transform on the spread spectrum sequence to obtain a time-domain sequence of the synchronization sequence, and send the time-domain sequence to a signal receiving device, so that the signal receiving device performs despreading processing on the time-domain sequence to obtain a synchronization sequence, and Time-frequency synchronization is performed using sequence units in the synchronization sequence.

The embodiments of the present invention do not limit the specific process of an inverse Fourier transform (IFFT, Inverse Fast Fourier Transform), and reference may be made to related technologies.

The process of generating the corresponding time-domain sequence by using the synchronization sequence will be described in detail below. Please refer to FIG. 2. FIG. 2 is a schematic diagram of generating a time-domain sequence using a synchronization sequence according to an embodiment of the present invention. Taking four spreading factors as an example, C[0] to C[3] represent spreading factors, The sequence on the far left of the figure is the synchronization sequence, and N represents the length of one OFDM symbol. Copy the synchronization sequence into four copies, place them in the sub-carrier channels determined by the spreading factor, and multiply the copied synchronization sequence with the corresponding spreading factor to obtain the spreading sequence, and finally perform the IFFT transformation on the spreading sequence. , the time domain sequence of the synchronization sequence can be obtained.

It can be understood that, after obtaining the time domain sequence, the sequence can also be subjected to OFDM modulation to obtain a corresponding modulated baseband signal, and finally the modulated baseband signal is sent to the signal receiving device. It can also be understood that the signal receiving device can also perform OFDM demodulation on the received modulated baseband signal. The embodiments of the present invention do not limit the specific manners of OFDM modulation and OFDM demodulation, and for details, reference may be made to related technologies of OFDM.

Further, the embodiments of the present invention do not limit the specific despreading processing steps of the time domain sequence by the signal receiving device. Reference may be made to related technologies of multi-carrier spreading. For example, the same spreading factor can be used to despread the time domain sequence. The embodiment of the present invention also does not limit the specific time domain synchronization process of the synchronization sequence by the signal receiving device, and for details, reference may be made to the related technology of time domain synchronization.

Further, it can be understood that in order to perform time domain synchronization, the synchronization sequence needs to have good autocorrelation and cross-correlation characteristics. Therefore, in the embodiment of the present invention, a synchronization sequence composed of a plurality of identical sequence units is used for timing synchronization, and these sequence units can meet the above-mentioned autocorrelation and cross-correlation requirements, and it is precisely these sequence units that are used to effectively Realize time domain synchronization of multi-carrier spread spectrum system. It should be noted that the embodiment of the present invention does not limit the specific manner of using the sequence unit of the synchronization sequence to perform time domain synchronization, and reference may be made to the related technology of time domain synchronization. The sequence unit is time-domain synchronized. It should be noted that the embodiments of the present invention do not limit the related content of the symbol timing estimation method and the frequency offset estimation method, and reference may be made to the related art.

。因此，所产生的调制基带信号

可以表示为The following briefly introduces the related content of multi-carrier spreading and despreading. In a possible situation, a signal transmitter of a multi-carrier spread spectrum system is shown in FIG. 3 , which is a schematic diagram of a transmitter of a multi-carrier spread spectrum system according to an embodiment of the present invention. For spread spectrum, the information symbols are converted into K channels of parallel information symbols (ie S[0] to S[K-1]) after serial-to-parallel conversion, and the K channels of parallel information symbols are regarded as a unit, and then each unit is Use the copy module to copy M copies, where M is the length of the spreading sequence. On this basis, each unit is first matched with an element of a spreading sequence (that is, any one of C(0) to C(M-1)) Multiply, and then use N -point IFFT for OFDM modulation, where

. Thus, the resulting modulated baseband signal

It can be expressed as

in,

表示指数运算，j表示

，t表示时刻。令

Represents exponential operation, j represents

, t represents time. make

but

Further, one can get

是

以周期为N的循环移位，因此，根据离散傅里叶变换（Discrete Fourier transform, DFT）的线性性质和循环移位性质有：As can be seen,

Yes

Circular shift with period N , therefore, according to the linear properties and cyclic shift properties of discrete Fourier transform (DFT):

as well as

相乘），在此基础上进行线性叠加（

操作），至此，即实现了解扩，完成了信号能量聚集，获得了扩频增益。在此基础上，利用窄带低通滤波器滤除带外噪声、镜像和干扰的影响，使信号中的干扰和噪声分量显著下降。而后利用通用OFDM系统的时频同步、信道估计等技术实现信号解调。Among them, IDFT (Inverse Discrete Fourier transform) is an inverse discrete Fourier transform. It can be seen that the frequency domain spread spectrum corresponds to the spectral shift in the time domain. Therefore, for the transmitting end of the multi-carrier spread spectrum system shown in FIG. 3 , the multi-carrier spread spectrum system is further provided with the receiving end of the multi-carrier spread spectrum system as shown in FIG. 4 , and FIG. Structural block diagram of the receiving end of the carrier spread spectrum system. Using the property of frequency domain spread spectrum corresponding to the spectrum shift in time domain, the multi-carrier spread spectrum system receiver first performs despreading operation, that is, firstly obtains M received signals through the replication module, and then compares each channel of received signals with the corresponding spread spectrum. The sequence elements (i.e. C(0) to C(M-1)) are multiplied together, followed by the corresponding spectral shift (i.e. with

Multiply), and then perform linear superposition on this basis (

operation), at this point, the despreading is realized, the signal energy aggregation is completed, and the spread spectrum gain is obtained. On this basis, a narrow-band low-pass filter is used to filter out the influence of out-of-band noise, image and interference, so that the interference and noise components in the signal are significantly reduced. Then, the time-frequency synchronization and channel estimation techniques of the general OFDM system are used to realize signal demodulation.

In a possible situation, the signal receiving device performs a despreading operation on the time domain sequence to obtain a synchronization sequence, and uses the sequence elements in the synchronization sequence to perform time-frequency synchronization, including:

Step 11: The signal receiving device uses the spreading factor to despread the received time domain sequence to obtain a synchronization sequence;

Step 12: Use the symbol timing estimation method and the frequency offset estimation method to perform time-frequency synchronization on the sequence units in the synchronization sequence.

可表示为：The following briefly introduces the related content of the symbol timing estimation method and the frequency offset estimation method. Taking the classic delay correlation synchronization algorithm as an example, the synchronization sequence is composed of two completely equal sequences in the time domain. Please refer to FIG. 5 , which is a schematic diagram of the classic delay correlation synchronization algorithm provided by an embodiment of the present invention. The metric function is constructed by delaying the correlation operation to obtain the best timing sampling point, and its metric function

can be expressed as:

in:

表示接收信号，

表示复数共轭运算，d表示滑动相关窗第一个采样点的序号，N表示一个OFDM符号的长度。则此时符号定时估计为：

Indicates the received signal,

represents the complex conjugate operation, d represents the sequence number of the first sampling point of the sliding correlation window, and N represents the length of one OFDM symbol. Then the symbol timing is estimated as:

便是对接收到的训练序列

进行延迟相关运算的结果。此外，其频偏估计的值也可以通过理想定时点处的延迟相关值来获得：in,

is the received training sequence

The result of performing a delay correlation operation. In addition, the value of its frequency offset estimation can also be obtained by the delay correlation value at the ideal timing point:

表示复数的相位，范围为

。可以看出，频偏估计的范围与同步序列的长度（即序列单元的结构）有关，同步序列越短，估计范围越大，但是估计精度越低；同步序列越长，估计精度越高，但估计范围越小。in,

represents the phase of a complex number in the range

. It can be seen that the range of frequency offset estimation is related to the length of the synchronization sequence (that is, the structure of the sequence unit). The shorter the synchronization sequence, the larger the estimation range, but the lower the estimation accuracy; the longer the synchronization sequence, the higher the estimation accuracy, but The smaller the estimated range.

Based on the above embodiment, the signal transmitting device in the present invention replicates the synchronization sequence according to the number of spreading factors, and multiplies the replicated synchronization sequence by the spreading factor to obtain the spreading sequence. In other words, the present invention The signal transmitting equipment in the device also performs spread spectrum processing on the synchronization sequence, and uses the spread spectrum obtained by the spread spectrum for subsequent data conversion and data transmission, which ensures that the signal receiving equipment can despread the spread spectrum sequence to restore the synchronization sequence. At the same time, the synchronization sequence used in the present invention is composed of a plurality of identical sequence units, which can ensure that the synchronization sequence contains a specific repetitive structure, and can flexibly adjust the parallel information symbols in the synchronization sequence to obtain long synchronization sequences and The short synchronization sequence can not only ensure that the signal receiving equipment can use the related method of time-frequency synchronization to perform time-frequency synchronization on the synchronization sequence, and ensure that the multi-carrier spread spectrum system can perform time-frequency synchronization normally, but also can use different types of synchronization sequences. Time-frequency synchronization with different precision improves the flexibility of time-frequency synchronization.

Based on the above embodiment, since the long synchronization sequence and the short synchronization sequence correspond to frequency offset estimation ranges of different precisions, when the two are combined, the application effect of rough estimation first and then accurate estimation can be achieved, which can improve the efficiency of time-frequency synchronization. In this embodiment of the present invention, the synchronization sequence may be a combination of a long synchronization sequence and a short synchronization sequence. The following describes the process of simultaneously using the long synchronization sequence and the short synchronization sequence to perform time-frequency synchronization.

In one possible case, a synchronization sequence is obtained, including:

S201, obtaining a long synchronization sequence and a short synchronization sequence;

Correspondingly, copy the synchronization sequence according to the preset number of spreading factors, and multiply the copied synchronization sequence by the spreading factor to obtain the spreading sequence, which may include:

S202. Copy the long synchronization sequence and the short synchronization sequence according to the preset number of spreading factors, and multiply the copied long synchronization sequence and the copied short synchronization sequence by the spreading factor respectively to obtain the long spreading sequence and the short synchronization sequence. Spreading sequence.

Correspondingly, performing inverse Fourier transform on the spread spectrum sequence to obtain the time-domain sequence of the synchronization sequence, and sending the time-domain sequence to the signal receiving device, may include:

S203: Perform inverse Fourier transform on the long spreading sequence and the short spreading sequence to obtain a long time domain sequence and a short time domain sequence.

S204, splicing the long time domain sequence and the short time domain sequence, so that the short time domain sequence is located at the front of the long time domain sequence, to obtain a total time domain sequence, and send the total time domain sequence to the signal receiving device.

In a possible situation, the signal receiving device performs a despreading operation on the time domain sequence to obtain a synchronization sequence, and performs time-frequency synchronization on the synchronization sequence, which may include:

S301. The signal receiving device performs despreading processing on the received time domain sequence by using the spreading factor to obtain a synchronization sequence.

S302. When the type of the synchronization sequence is a short synchronization sequence, use the symbol timing estimation method and the frequency offset estimation method to perform first time-frequency synchronization on the sequence elements in the synchronization sequence, and determine the initial frequency offset estimation range.

S303. When the type of the synchronization sequence is a long synchronization sequence and the initial frequency offset estimation range is determined, within the initial frequency offset range, use the symbol timing estimation method and the frequency offset estimation method to perform a second time-frequency analysis on the sequence units in the synchronization sequence Synchronize to determine the final frequency offset estimation range.

Based on the above embodiment, considering that the shorter the synchronization sequence is, the larger the estimation range is, but the lower the estimation accuracy is, and the longer the synchronization sequence is, the higher the estimation accuracy is, but the smaller the estimation range is. In order to further improve the efficiency of time domain synchronization, this The signal transmitting device in the embodiment of the invention can spliced and transmit the short synchronization sequence and the long synchronization sequence, so that the signal receiving device first uses the short synchronization sequence to perform initial time-frequency synchronization, determines the initial frequency offset estimation range, and then performs frequency offset Within the estimated range, the long synchronization sequence is used to further perform time-frequency synchronization to determine the final frequency offset estimation range, which can effectively improve the efficiency and accuracy of time-frequency synchronization.

The communication system and storage medium provided by the embodiments of the present invention are introduced below. The communication system and storage medium described below and the time-frequency synchronization method described above can be referred to each other correspondingly.

Please refer to FIG. 10. FIG. 10 is a structural block diagram of a communication system provided by an embodiment of the present invention. The system may include: a signal transmitting device 1001 and a signal receiving device 1002, wherein,

，且并行信息符号的信号值同时存在零和非零值时，同步序列为短同步序列；依照预设的扩频因子的数量复制同步序列，并将复制后的同步序列与扩频因子相乘，得到扩频序列；将扩频序列进行反向傅里叶变换得到同步序列的时域序列，并将时域序列发送至信号接收设备1002；The signal transmitting device 1001 is used to obtain a synchronization sequence; the synchronization sequence is composed of a plurality of identical sequence units, and the sequence units are composed of parallel information symbols; when the number of parallel information symbols in the sequence unit is 1, and the signal values of the parallel information symbols are not When it is zero, the synchronization sequence is a long synchronization sequence; when the number of parallel information symbols in the sequence unit is

, and when the signal values of the parallel information symbols have both zero and non-zero values, the synchronization sequence is a short synchronization sequence; the synchronization sequence is copied according to the preset number of spreading factors, and the copied synchronization sequence is multiplied by the spreading factor to obtain a spread spectrum sequence; perform inverse Fourier transform on the spread spectrum sequence to obtain a time domain sequence of the synchronization sequence, and send the time domain sequence to the signal receiving device 1002;

The signal receiving device 1002 is configured to perform a despreading operation on a time domain sequence to obtain a synchronization sequence, and use the synchronization sequence to perform time-frequency synchronization.

Optionally, the signal transmitting device 1001 is also used to obtain the long synchronization sequence and the short synchronization sequence; copy the long synchronization sequence and the short synchronization sequence according to the preset number of spreading factors, and respectively copy the copied long synchronization sequence and the copied long synchronization sequence. Multiply the short synchronization sequence and the spreading factor to obtain the long spreading sequence and the short spreading sequence; perform the inverse Fourier transform on the long spreading sequence and the short spreading sequence to obtain the long time domain sequence and the short time domain sequence sequence; splicing the long time domain sequence and the short time domain sequence, so that the short time domain sequence is located in the front of the long time domain sequence, to obtain the total time domain sequence, and send the total time domain sequence to the signal receiving device 1002 .

Optionally, the signal receiving device 1002 is further configured to perform despread processing on the received time-domain sequence by using a spreading factor to obtain a synchronization sequence; and use the symbol timing estimation method and the frequency offset estimation method to perform despreading processing on the sequence unit included in the synchronization sequence. Time-frequency synchronization is performed.

Optionally, the signal receiving device 1002 is further configured to perform despread processing on the received time domain sequence by using a spreading factor to obtain a synchronization sequence; perform Fourier transform on the synchronization sequence, and perform Fourier transform on the synchronization sequence, The value of each parallel information symbol of , determines the type of the synchronization sequence; when the type of the synchronization sequence is a short synchronization sequence, the first time-frequency synchronization is performed on the sequence units in the synchronization sequence by using the symbol timing estimation method and the frequency offset estimation method to determine the initial Frequency offset estimation range; when the type of the synchronization sequence is a long synchronization sequence and the initial frequency offset estimation range is determined, within the initial frequency offset range, the symbol timing estimation method and the frequency offset estimation method are used to perform the first step on the sequence units in the synchronization sequence. Two time-frequency synchronization, determine the final frequency offset estimation range.

Embodiments of the present invention further provide a storage medium, where a computer program is stored on the storage medium, and when the computer program is executed by a processor, the steps of the time-frequency synchronization method in any of the foregoing embodiments are implemented.

Since the embodiments of the storage medium part correspond to the embodiments of the time-frequency synchronization method part, the embodiments of the storage medium part refer to the description of the embodiments of the time-frequency synchronization method part, which will not be repeated here.

The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other. As for the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant part can be referred to the description of the method.

Professionals may further realize that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two, in order to clearly illustrate the possibilities of hardware and software. Interchangeability, the above description has generally described the components and steps of each example in terms of functionality. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Skilled artisans may implement the described functionality using different methods for each particular application, but such implementations should not be considered beyond the scope of the present invention.

The steps of a method or algorithm described in conjunction with the embodiments disclosed herein may be directly implemented in hardware, a software module executed by a processor, or a combination of the two. Software modules can be placed in random access memory (RAM), internal memory, read only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other in the technical field. in any other known form of storage medium.

A time-frequency synchronization method, a communication system and a storage medium provided by the present invention have been introduced in detail above. The principles and implementations of the present invention are described herein by using specific examples, and the descriptions of the above embodiments are only used to help understand the method and the core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can also be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims (8)

1. A time-frequency synchronization method is characterized by comprising the following steps:

the signal transmitting equipment acquires a synchronization sequence; the synchronous sequence is composed of a plurality of identical sequence units, and the sequence units are composed of parallel information symbols; when the number of the parallel information symbols in the sequence unit is 1 and the signal value of the parallel information symbols is notWhen the time is zero, the synchronization sequence is a long synchronization sequence; when the number of the parallel information symbols in the sequence unit is as

When the signal value of the parallel information symbol has zero and non-zero values at the same time, the synchronization sequence is a short synchronization sequence;

copying the synchronous sequence according to the number of preset spreading factors, and multiplying the copied synchronous sequence by the spreading factors to obtain a spreading sequence;

and performing inverse Fourier transform on the spread spectrum sequence to obtain a time domain sequence of the synchronous sequence, sending the time domain sequence to signal receiving equipment so that the signal receiving equipment performs de-spreading processing on the time domain sequence to obtain the synchronous sequence, and performing time-frequency synchronization by using a sequence unit in the synchronous sequence.

2. The time-frequency synchronization method according to claim 1, wherein the acquiring the synchronization sequence comprises:

acquiring the long synchronization sequence and the short synchronization sequence;

correspondingly, the copying the synchronization sequence according to the number of the preset spreading factors, and multiplying the copied synchronization sequence by the spreading factors to obtain a spreading sequence includes:

copying the long synchronization sequence and the short synchronization sequence according to the number of preset spreading factors, and multiplying the copied long synchronization sequence and the copied short synchronization sequence by the spreading factors to obtain a long spreading sequence and a short spreading sequence;

correspondingly, the performing inverse fourier transform on the spreading sequence to obtain a time domain sequence of the synchronization sequence, and sending the time domain sequence to a signal receiving device includes:

performing the inverse Fourier transform on the long spreading sequence and the short spreading sequence to obtain a long time domain sequence and a short time domain sequence;

and splicing the long time domain sequence and the short time domain sequence to enable the short time domain sequence to be positioned in front of the long time domain sequence to obtain a total time domain sequence, and sending the total time domain sequence to the signal receiving equipment.

3. The time-frequency synchronization method according to claim 1, wherein the signal receiving device performs despreading processing on the time-domain sequence to obtain the synchronization sequence, and performs time-frequency synchronization by using sequence units in the synchronization sequence, including:

the signal receiving equipment performs the despreading processing on the received time domain sequence by using the spreading factor to obtain the synchronization sequence;

and carrying out time-frequency synchronization on the sequence units in the synchronization sequence by utilizing a symbol timing estimation method and a frequency offset estimation method.

4. The time-frequency synchronization method according to claim 3, wherein the performing time-frequency synchronization on the sequence units in the synchronization sequence by using the symbol timing estimation method and the frequency offset estimation method comprises:

when the type of the synchronization sequence is the short synchronization sequence, performing first time-frequency synchronization on sequence units in the synchronization sequence by using the symbol timing estimation method and the frequency offset estimation method to determine an initial frequency offset estimation range;

when the type of the synchronization sequence is the long synchronization sequence and the initial frequency offset estimation range is determined, within the initial frequency offset range, performing second time-frequency synchronization on sequence units in the synchronization sequence by using the symbol timing estimation method and the frequency offset estimation method, and determining a final frequency offset estimation range.

5. A communication system, comprising: a signal transmitting apparatus and a signal receiving apparatus, wherein,

the signal transmitting equipment is used for acquiring a synchronization sequence; the synchronization sequence is composed of a plurality of identical sequence units, and the sequence units are composed of parallel information symbolsNumber composition; when the number of the parallel information symbols in the sequence unit is 1 and the signal value of the parallel information symbols is not zero, the synchronization sequence is a long synchronization sequence; when the number of the parallel information symbols in the sequence unit is as

When the signal value of the parallel information symbol has zero and non-zero values at the same time, the synchronization sequence is a short synchronization sequence; copying the synchronous sequence according to the number of preset spreading factors, and multiplying the copied synchronous sequence by the spreading factors to obtain a spreading sequence; performing inverse Fourier transform on the spread spectrum sequence to obtain a time domain sequence of the synchronous sequence, and sending the time domain sequence to the signal receiving equipment;

and the signal receiving equipment is used for carrying out de-spreading processing on the time domain sequence to obtain the synchronization sequence and carrying out time-frequency synchronization by utilizing the sequence unit in the synchronization sequence.

6. The communication system according to claim 5, wherein the signal transmitting apparatus is further configured to obtain a long synchronization sequence and a short synchronization sequence; copying the long synchronization sequence and the short synchronization sequence according to the number of preset spreading factors, and multiplying the copied long synchronization sequence and the copied short synchronization sequence by the spreading factors to obtain a long spreading sequence and a short spreading sequence; performing inverse Fourier transform on the long spreading sequence and the short spreading sequence to obtain a long time domain sequence and a short time domain sequence; and splicing the long time domain sequence and the short time domain sequence to enable the short time domain sequence to be positioned in front of the long time domain sequence to obtain a total time domain sequence, and sending the total time domain sequence to the signal receiving equipment.

7. The communication system according to claim 5, wherein the signal receiving apparatus is further configured to perform the despreading process on the received time domain sequence by using the spreading factor to obtain a synchronization sequence; and performing the time-frequency synchronization on the sequence unit in the synchronization sequence by using a symbol timing estimation method and a frequency offset estimation method.

8. A storage medium having stored thereon computer-executable instructions which, when loaded and executed by a processor, carry out a time-frequency synchronization method according to any one of claims 1 to 4.

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