CN107276951B

CN107276951B - Carrier synchronization method and device

Info

Publication number: CN107276951B
Application number: CN201610216953.0A
Authority: CN
Inventors: 不公告发明人
Original assignee: Shenzhen Kuang Chi Hezhong Technology Ltd
Current assignee: Liaoning Power Energy Development Group Co ltd
Priority date: 2016-04-08
Filing date: 2016-04-08
Publication date: 2021-08-06
Anticipated expiration: 2036-04-08
Also published as: CN107276951A

Abstract

The invention provides a carrier synchronization method, which comprises the following steps: performing a cross-correlation operation on two LAS codes extracted from a received signal to obtain a frequency offset of a carrier between a receiving end and a transmitting end, wherein the received signal is a time domain signal from the transmitting end and comprises a training sequence based on the LAS codes; and performing frequency offset correction on the received signal based on the frequency offset. The invention improves the frequency deviation precision of the system and reduces the error rate of the whole system.

Description

Carrier synchronization method and device

Technical Field

The present invention relates generally to wireless communication systems, and more particularly, to a carrier synchronization method and apparatus.

Background

Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and so on. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Examples of such multiple-access networks include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, orthogonal FDMA (ofdma) networks, and single carrier FDMA (SC-FDMA) networks.

With the increasing demand of global mobile communication, the frequency resources of wireless communication are becoming more and more tight. Therefore, in addition to the above-described conventional high spectrum utilization wireless communication system based on TDM (time division multiplexing), FDM (frequency division multiplexing), a more aggressive communication scheme with higher utilization of the spectrum has been proposed.

An Overlapped Time Division Multiplexing (OvTDM) system is one such scheme for improving the spectrum efficiency of the system. In an OvTDM system, the symbols do not need to be isolated from each other, but may overlap strongly. In other words, the OvTDM system artificially introduces overlap between symbols, and uses a plurality of symbols to transmit data sequences in parallel in the time domain, thereby greatly improving the spectrum utilization rate.

An Overlapped Frequency Division Multiplexing (OvFDM) system is another scheme for improving the spectral efficiency of a system. In an OvFDM system, there may be a stronger overlap between sub-carrier bands than orthogonal frequency division multiplexing, OFDM. The frequency spectrum utilization rate is further improved on the basis of the OFDM system through the higher overlapping degree among the sub-frequency bands in the frequency domain.

Although the OvTDM system and the OvFDM system have corresponding receiving demodulation schemes to eliminate interference caused by overlapping of signals in the time domain or the frequency domain, a great improvement in the spectrum utilization rate still puts higher demands on the signal reception.

Therefore, the OvTDM system and the OvFDM system require a higher performance network access scheme. The m-sequence carrier synchronization method adopted by the existing communication system cannot meet the requirement.

Disclosure of Invention

The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

The invention aims to provide a carrier synchronization method and a carrier synchronization device to solve the problems that when the existing communication system adopts m sequences for carrier synchronization, the carrier frequency offset deviation is large and the synchronization result is inaccurate due to poor autocorrelation and cross-correlation characteristics.

According to an aspect of the present invention, there is provided a carrier synchronization method, including:

performing a cross-correlation operation on two LAS codes extracted from a received signal to obtain a frequency offset of a carrier between a receiving end and a transmitting end, wherein the received signal is a time domain signal from the transmitting end and comprises a training sequence based on the LAS codes; and

a frequency offset correction is performed on the received signal based on the frequency offset.

In one example, the training sequence includes two LAS short codes [ X ]_las]_SNAnd SN is the length of the LAS short code, wherein the performing a cross-correlation operation on the two LAS codes extracted from the received signal to obtain a frequency offset of a carrier between the receiving end and the transmitting end includes:

performing a cross-correlation operation on the two LAS short codes extracted from the received signal to obtain a coarse frequency offset of a carrier between a receiving end and a transmitting end, an

The performing frequency offset correction on the received signal based on the frequency offset includes:

performing a first frequency offset correction on the received signal based on the coarse frequency offset.

In one example, the training sequence includes [0 ]]_SN,[X_las]_SN,[0]_SN,[X_las]_SNWherein [0 ]]_SNIs a 0 sequence of length SN.

In one example, the training sequence also includes two LAS long codes [ X ]_las]_LNLN is the length of the LAS long code, wherein the performing cross-correlation operation on the two LAS codes extracted from the received signal to obtain the frequency offset of the carrier between the receiving end and the transmitting end further comprises:

performing a cross-correlation operation on two LAS long codes extracted from the received signal subjected to the primary frequency offset correction to obtain a fine frequency offset of a carrier between a receiving end and a transmitting end, an

The performing frequency offset correction on the received signal based on the frequency offset further comprises:

and performing secondary frequency offset correction on the received signal subjected to the primary frequency offset correction based on the coarse frequency offset and the fine frequency offset.

In one example, the performing secondary frequency offset correction on the received signal subjected to the primary frequency offset correction based on the coarse frequency offset and the fine frequency offset includes:

and performing the secondary frequency offset correction on the received signal subjected to the primary frequency offset correction based on the sum of the coarse frequency offset and the fine frequency offset.

In one example, the training sequence includes [0 ]]_SN,[X_las]_SN,[0]_SN,[X_las]_SN,[X_las]_LN,[X_las]_LNWherein [0 ]]_SNIs a 0 sequence of length SN.

In an example, the two LAS short codes and extraction positions of the two LAS long codes are also used for timing synchronization, which are determined based on a result of the timing synchronization.

According to another aspect of the present invention, there is provided a carrier synchronization apparatus, including:

a cross-correlation calculation unit, configured to perform a cross-correlation operation on two LAS codes extracted from a received signal to obtain a frequency offset of a carrier between a receiving end and a transmitting end, where the received signal is a time domain signal from the transmitting end and includes a training sequence based on the LAS codes; and

a frequency correction unit for performing frequency offset correction on the received signal based on the frequency offset.

In one example, the training sequence includes two LAS short codes [ X ]_las]_SNSN is the length of the LAS short code, wherein the correlation calculation unit is further configured to perform a cross-correlation operation on the two LAS short codes extracted from the received signal to obtain a coarse frequency offset of the carrier between the receiving end and the transmitting end, and

the frequency correction unit is further configured to perform a first time frequency offset correction on the received signal based on the coarse frequency offset.

In one example, the training sequence also includes two LAS long codes [ X ]_las]_LNLN is the length of the LAS long code, wherein the correlation calculation unit is further configured to perform a cross-correlation operation on the two LAS long codes extracted from the received signal subjected to the primary frequency offset correction to obtain a fine frequency offset of the carrier between the receiving end and the transmitting end, and

the frequency correction unit is further configured to perform secondary frequency offset correction on the received signal subjected to the primary frequency offset correction based on the coarse frequency offset and the fine frequency offset.

In an example, the frequency correction unit is further configured to perform the secondary frequency offset correction on the received signal subjected to the primary frequency offset correction based on a sum of the coarse frequency offset and the fine frequency offset.

The invention has the following beneficial effects: the invention designs LAS code training sequence in communication system, using LAS code self-correlation function as ideal impact function at original point, zero at position outside original point and zero at position of cross-correlation function, using LAS code as carrier synchronization in signal receiving process. When the LAS code is adopted for carrier synchronization, the frequency offset precision of the system is improved through two synchronization processes of coarse synchronization of the short LAS code and fine synchronization of the long LAS code, a foundation is laid for a subsequent channel estimation process and a subsequent decoding process, and the error rate of the whole system is reduced.

Drawings

The above features and advantages of the present disclosure will be better understood upon reading the detailed description of embodiments of the disclosure in conjunction with the following drawings. In the drawings, components are not necessarily drawn to scale, and components having similar relative characteristics or features may have the same or similar reference numerals.

Fig. 1 shows a block diagram of a transmit side modulation module of an OvTDM system;

fig. 2 shows a block diagram of a signal pre-processing module at the receiving end of the OvTDM system;

FIG. 3 shows a block diagram of a receive end sequence detection module of the OvTDM system;

fig. 4 shows a block diagram of the modulation modules at the transmitting end of the OvFDM system;

fig. 5 shows a block diagram of a signal pre-processing module at the receiving end of the OvFDM system;

fig. 6 shows a block diagram of a signal detection module at the receiving end of the OvFDM system;

fig. 7 shows the autocorrelation characteristic of the M sequence;

fig. 8 illustrates an autocorrelation characteristic of an LAS code;

FIG. 9 shows a distribution diagram of autocorrelation results for timing synchronization;

FIG. 10 shows a schematic diagram of a training sequence in the case where two peaks are detected;

fig. 11 illustrates a block diagram of a timing synchronization unit of a receiving end in accordance with an aspect of the present invention;

FIG. 12 illustrates a flow chart diagram of a timing synchronization methodology in accordance with an aspect of the subject invention;

fig. 13 illustrates a block diagram of a carrier synchronization unit in accordance with an aspect of the subject innovation;

fig. 14 illustrates a flow chart of a carrier synchronization method in accordance with an aspect of the invention;

fig. 15 illustrates a flow chart of a carrier synchronization method in accordance with an aspect of the invention;

fig. 16 shows a schematic diagram of an arrangement of multipath channels;

FIG. 17 illustrates a plot of training sequence and data bandwidth versus power spectral density in accordance with an aspect of the subject invention; and

fig. 18 shows a schematic diagram of a frequency spectrum when two carrier signals simultaneously transmit data according to an aspect of the invention.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments. It is noted that the aspects described below in connection with the figures and the specific embodiments are only exemplary and should not be construed as imposing any limitation on the scope of the present invention.

In addition to being applied to OvTDM and OvFDM systems, the techniques described herein can be widely applied to actual mobile communication systems, such as TD-LTE, TD-SCDMA, etc., and also can be widely applied to any wireless communication systems, such as satellite communication, microwave line-of-sight communication, scattering communication, atmospheric optical communication, infrared communication, and aquatic communication. The terms "network" and "system" are often used interchangeably.

The continuous development of mobile communication and the endless emergence of new services put higher and higher requirements on data transmission rate, while the frequency resources of mobile communication are very limited, and how to realize high-speed data transmission by using the limited frequency resources becomes an important problem faced by the current mobile communication technology

The OvTDM and OvFDM systems described above are just such solutions that can greatly improve spectrum utilization. The transmission and reception process of the OvTDM system will be briefly described below.

The OvTDM system uses multiple symbols to transmit data sequences in parallel in the time domain. And a transmitting end forms a transmitting signal with a plurality of symbols mutually overlapped on a time domain, and a receiving end detects the receiving signal according to the data sequence in the time domain according to the one-to-one correspondence between the time waveforms of the transmission data sequence and the transmission data sequence. The OvTDM system actively utilizes the overlapping to generate a coding constraint relation, thereby greatly improving the spectral efficiency of the system.

Fig. 1 shows a block diagram of a transmit side modulation module of an OvTDM system. The transmit-side modulation module 100 may include a digital waveform generation unit 110, a shift register unit 120, a multiplication unit 130, and an addition unit 140.

Firstly, the digital waveform generating unit 110 digitally designs and generates the first modulated signal envelope waveform h (T) of the transmission signal, the shift registering unit 120 shifts the envelope waveform h (T) for a specific time to form the envelope waveforms h (T-i × Δ T) of the modulated signals at other times, the multiplying unit 130 multiplies the parallel symbols x to be transmitted_iMultiplying the envelope waveform h (T-i multiplied by delta T) of the corresponding moment to obtain the modulated signal waveform x to be transmitted at each moment_ih (T-i.times.DELTA.T). The adding unit 140 superimposes the formed waveforms to be transmitted to form a transmitted signal waveform.

The receiving end of the OvTDM system is mainly divided into a signal preprocessing module 200 and a sequence detection module 300. Fig. 2 shows a block diagram of a signal pre-processing module 200 at the receiving end of the OvTDM system. The signal preprocessing module is used to assist in forming the synchronous received digital signal sequence within each frame, and as shown, may include a synchronization unit 210, a channel estimation unit 220, and a digitization processing unit 230.

The synchronization unit 210 is configured to form symbol synchronization in the time domain for the received signal to maintain a synchronization state with the system, and mainly includes timing synchronization and carrier synchronization. After synchronization, the channel estimation unit 220 performs channel estimation on the received signal to estimate parameters of an actual transmission channel. The digitization processing unit 230 is configured to perform digitization processing on the received signal within each frame, so as to form a sequence of received digital signals suitable for sequence detection by the sequence detection portion.

After preprocessing, the received signal may be sequence detected in the sequence detection module 300, the received waveform may be sliced according to the waveform transmission time interval and the sliced waveform may be decoded according to a certain decoding algorithm. Fig. 3 shows a block diagram of a receive end sequence detection module of the OvTDM system. As shown, the sequence detection module 300 may include an analysis storage unit 310, a comparison unit 320, and a reserve path storage unit and euclidean distance storage unit 330. In the detection process, the analysis storage unit makes a complex convolution coding model and a trellis diagram of the OvTDM system, and lists and stores all the states of the OvTDM system. The comparison unit searches out the path with the minimum Euclidean distance from the received digital signal according to the trellis diagram in the analysis storage unit, and the reserved path storage unit and the Euclidean distance storage unit are respectively used for storing the reserved path and the Euclidean distance or the weighted Euclidean distance output by the comparison unit. The reserved path memory unit and the euclidean distance memory unit need to be prepared one for each steady state. The reserved path memory cell length may preferably be 4K to 5K. The euclidean distance storage unit preferably stores only the relative distance.

Fig. 4 shows a block diagram of the modulation module at the transmitting end of the OvFDM system. The OvFDM modulation module at the transmitting end may include a modulated carrier spectrum generation unit 410, a carrier spectrum shift unit 420, a multiplication unit 430, an addition unit 440, and an inverse fourier transform unit 450.

Firstly, the modulated carrier spectrum generating unit 410 is designed to generate an envelope spectrum signal H (f) of a subcarrier, and the carrier spectrum shifting unit 420 shifts the envelope spectrum signal H (f) sequentially by a specific carrier spectrum interval Δ B to obtain an envelope spectrum signal of the next subcarrier, shifts the envelope spectrum signal of the next subcarrier by the specific carrier spectrum interval Δ B, and sequentially obtains spectrum waveforms H (f-i × Δ B) of all subcarriers with spectrum intervals Δ B.

The multiplying unit 430 multiplies the multiple parallel symbols X to be transmitted_iMultiplying the obtained frequency spectrum waveform with each generated corresponding subcarrier frequency spectrum waveform H (f-i multiplied by delta B) respectively to obtain a plurality of modulation signal frequency spectrums X modulated by corresponding subcarriers_iH(f-i×ΔB)。

The addition unit 440 superimposes the formed multi-path modulated signal spectrumForming a spectrum of the complex modulated signal

Finally, inverse Fourier transform unit 450 performs inverse discrete Fourier transform on the frequency spectrum of the generated complex modulation signal to finally form time-domain complex modulation signal (t)_TX＝ifft(S(f))。

The receiving end of the OvFDM system is mainly divided into a signal preprocessing module 500 and a signal detecting module 600. Fig. 5 shows a block diagram of a signal preprocessing module at the receiving end of the OvFDM system. As shown, the preprocessing module may include a synchronization unit 510, a channel estimation unit 520, and a digitization processing unit 530.

The synchronization unit 510 is configured to form symbol synchronization for the received signal in the time domain to maintain a synchronization state with the system, and mainly includes timing synchronization and carrier synchronization. After synchronization, the channel estimation unit 520 performs channel estimation on the received signal to estimate parameters of an actual transmission channel. The digital processing unit 530 is used for sampling and quantizing the received signal of each symbol time interval into a digital signal sequence.

After preprocessing, the received signal may be detected in the signal detection module 600. Fig. 6 shows a block diagram of a signal detection module 600 at the receiving end of the OvFDM system. As shown, the signal detection module 600 may include a fourier transform unit 610, a frequency segmentation unit 620, a convolutional encoding unit 630, and a data detection unit 640. The fourier transform unit 610 is configured to convert the preprocessed time domain signal into a frequency domain signal, i.e. fourier transform the received digital signal sequence of each time symbol interval to form an actual received signal spectrum of each time symbol interval. The frequency segmentation unit 620 is configured to segment the actual received signal spectrum for each time symbol interval in the frequency domain with a spectral interval Δ B to form an actual received signal segmented spectrum. The convolutional coding unit 630 is used to form a one-to-one correspondence between the received signal spectrum and the transmitted data symbol sequence. The data detection unit 640 is configured to detect a data symbol sequence according to a one-to-one correspondence relationship formed by the convolutional coding units.

The above describes the OvTDM system and the processing procedure at the transmitting and receiving ends of the OvTDM system. Although the OvTDM system and the OvFDM system have corresponding receiving demodulation schemes to eliminate interference caused by overlapping of signals in the time domain or the frequency domain, a great improvement in the spectrum utilization rate still puts higher demands on the signal reception.

In general communication systems, training sequences need to be designed, and the functions of the training sequences are mainly to realize timing synchronization, carrier synchronization and channel estimation through processing after signals are received. Timing synchronization, carrier synchronization and channel estimation are three most important links for correct receiving of a receiving end. The design of the training symbols is therefore of crucial importance, especially for ultra high frequency spectrally efficient communication systems such as the OvTDM and OvFDM systems. If any one of the three steps has a large error, the influence on the whole system is large, and the subsequent decoding process is not meaningful.

At present, an M sequence is often adopted as a training sequence in a communication system, and due to the poor self-correlation and cross-correlation characteristics of the M sequence, the success rate of a system synchronization process is low, and network access is slow. Fig. 7 shows the autocorrelation characteristic of the M-sequence, and it can be seen that the autocorrelation characteristic is not good because pulses appear at certain time intervals. Therefore, in the signal processing process, the synchronization precision of time and frequency is poor, the success rate and the access speed of a user accessing a network are reduced, and the user experience is poor.

According to an aspect of the present invention, a training sequence is designed using LAS codes in both an OvTDM system and an OvFDM system. It has been found that LAS codes have the property that the autocorrelation function is an ideal impulse function at the origin, and is zero everywhere outside the origin, while the cross-correlation function is zero everywhere. This is an extremely advantageous property for the training sequence.

The LAS (Large Area Synchronized) code is composed of a series of pulses and 0-valued pulse intervals of unequal length, and can be represented as (N, K, L), where N represents the number of pulses, K represents the shortest interval length between pulses, and L represents the code length. The pulse is generated by a complete complementary orthogonal code and is characterized in that the autocorrelation function is an ideal impulse function at the origin, the autocorrelation function is zero everywhere except the origin, and the cross-correlation function is zero everywhere. The characteristic of the LAS code is applied to an OvTDM system and an OvFDM system, and the synchronization success rate and the access speed of the whole system are improved.

A method of generating the LAS code is briefly described below.

The complete complementary orthogonal code has a dual relation, and the generation method is to solve another pair of the shortest basic complementary codes which are completely orthogonal and complementary with the shortest basic complementary code according to the shortest basic complementary code. In this case, the complete complementary orthogonal code is generated by the basic short code +++ -as follows:

C₀＝[1 1]corresponding to ++, S₀＝[1 -1]Corresponding to + -, according to C₀And S₀Respectively obtain their complementary codes C₁And S₁。C₁Is a pair of S₀Get the inverse of to obtain S₁Is a pair C₀Negation is performed and negation is performed, and the code in matlab is expressed as:

C₁＝fliplr(S₀)，S₁-1 × conj (fliplr (C0)). Wherein, the fliplr is a function for inverting the matrix left and right along a vertical axis, and the conj is a function for solving complex conjugate.

From this, C is obtained₁＝[-1 1],S₁＝[-1 -1]Mixing C with₀ C₁The combination generates a new complementary code C₀'＝[1 1 -1 1]，S₀'＝[1 -1 -1 -1]At this time, the length of each complementary code is extended from 2 to 4.

Here, the length L of the complementary code can be designed_N(L_NTo the power of 2), i.e., C_nAnd S_nAre respectively L_N/2. By adopting the method, the generated LAS code is iterated, and the length of the LAS code is expanded to L_NThe number of iterations is log₂L_N-2, the resulting complementary code is C_n、S_n。

Combining the pair of complementary codes and the zero sequence to generate the LAS code, expressed as: (la ═ C)_n L₀ S_n]Wherein L is₀Denotes the number of 0, i.e. C_nAnd S_nThe length of the shortest interval therebetween, and the final generated LAS code length is expressed asL＝L_N+L₀。

Fig. 8 illustrates an autocorrelation characteristic of the LAS code.

According to an aspect of the present invention, LAS codes are employed to design training sequences.

For the purpose of timing synchronization, the training sequence includes at least one LAS code. Since the LAS short code still has better synchronization effect under the condition of larger frequency deviation, the training sequence preferably comprises at least one LAS short code, so as to [ X ] X_las]_SNWherein the length of the LAS short code is denoted as SN, and the length of the complementary code and the length of the zero sequence are denoted as L_short-N、L_Short-0，SN＝L_short-N+L_Short-0。

To further optimize the autocorrelation characteristic of the LAS code, a zero sequence of the same length as the LAS short code may be included before the LAS short code, to [0 ]]_SNAnd (4) showing.

In particular embodiments, the training sequence may include two identical LAS short codes, such that in the case where one of the LAS short codes may be used for timing synchronization, a LAS short code pair may also be formed with the other LAS short code for carrier synchronization.

For carrier synchronization purposes, the training sequence may include at least one pair of identical LAS codes. Since the LAS short code still has a good synchronization effect under the condition of large frequency offset, the training sequence preferably includes at least one pair of the same LAS short codes.

Preferably, the carrier synchronization can be divided into two stages, i.e., coarse carrier synchronization and fine carrier synchronization. Thus, the training sequence may include at least two pairs of LAS codes. Preferably, one pair of LAS codes may be the same LAS short code for carrier coarse synchronization and the other pair of LAS codes may be the same LAS long code for carrier fine synchronization. LAS Long code available [ X ]_las]_LNWherein the length of the LAS long code is denoted as LN, and the length of the complementary code and the length of the zero sequence are denoted as L_length-N、L_Length-0，LN＝L_length-N+L_Length-0。

In order to further optimize the cross-correlation characteristics of the LAS codes, the same as the LAS short codes may be further included before each LAS short codeA sequence of zeros of length, in [0 ]]_SNAnd (4) showing.

For the purpose of channel estimation, the training sequence may include at least one LAS code, for example, one LAS long code, or may also include two LAS long codes, and two times of channel estimation are performed for the two LAS long codes, thereby improving the success rate of channel estimation.

As a specific example, L may be designed_length-N＝256，L_Length-0＝16；L_short-N＝16，L_Short-08. Of course, the lengths of the LAS long code and the LAS short code are shown here as an example, and other lengths may be designed.

As a preferred embodiment, an LAS code training sequence satisfying timing synchronization, carrier synchronization and channel estimation at the same time can be designed as follows: [0]_SN,[X_las]_SN,[0]_SN,[X_las]_SN,[X_las]_LN,[X_las]_LN. In this embodiment, the first LAS code is a short code, which can achieve timing synchronization, and the LAS short code still has a good synchronization effect when the frequency offset is large. The first and second LAS short codes may be used for coarse carrier synchronization, with the benefit of short codes being able to handle larger frequency offsets. The last two LAS codes are long codes and can be used for fine frequency offset correction and channel estimation.

Timing synchronization procedure

The receiver receives the signal and needs to maintain synchronization with the communication system, including timing synchronization and carrier synchronization. The principle of timing synchronization is to directly calculate the autocorrelation operation of the received signal and the local LAS code by a matched filtering method to obtain the autocorrelation peak value. And finding the position of the training symbol from the correlation peak according to a certain method. Finding the position of the training symbol also determines the initial position of the current frame, i.e. the time synchronization of the received signal and the system is completed, and the timing synchronization process is finished.

As described above, since the auto-correlation and cross-correlation characteristics of the LAS code are good, the LAS code is used to design training symbols. Therefore, when the correlation operation of the received signal and the LAS code is calculated, the distribution difference of the peak values is large, the initial position of the LAS code can be accurately found through reasonably setting the threshold value, and the timing precision is high.

Specifically, when searching for the correlation peak of the LAS code, a proper signal receiving length is adopted according to a training symbol structure, and a sliding window autocorrelation operation mode is used to perform correlation operation on a received signal and the local LAS code to search for the autocorrelation peak to determine the position of the LAS code. For example, the signal reception length here can be guaranteed to cover at least the LAS code to ensure that a peak can be detected.

The so-called sliding window autocorrelation operation is to perform windowing on a received signal with the length of the LAS code as the window length, and perform correlation operation on the signal in the current window and the local LAS code, thereby obtaining an autocorrelation result. Then, the window is slid backwards, the received signal is windowed, and the signal in the current window and the local LAS code are correlated, so as to obtain a correlation result. In this way, the window is continuously slid until all of the received signals have been correlated. From all the autocorrelation results obtained by the calculation, the position of the LAS code is found by setting a threshold, that is, the autocorrelation result exceeding the threshold as a peak.

In one example, only one LAS code, e.g., one LAS short code, is included in the training sequence because the short code still has a good synchronization effect in the case of large frequency offset. In this case, the length of the LAS short code may be used as a window length to perform windowing on the received signal, and the segment of the signal in the current window may be correlated with the local LAS short code to obtain an autocorrelation result. Then, the window is slid backwards, the received signal is windowed, and the signal in the current window and the local LAS code are correlated, so as to obtain a correlation result. In this way, the window is continuously slid until all of the received signals have been correlated. From all the autocorrelation results obtained by the calculation, the position of the LAS code is found by setting a threshold, that is, the autocorrelation result exceeding the threshold as a peak.

In the case of a multipath channel, it may occur that the amplitude of the following paths is higher than the amplitude of the first path, and the first peak point exceeding the threshold should be selected, not necessarily the global maximum. Fig. 9 shows a distribution diagram of autocorrelation results of timing synchronization. Assuming that the threshold is 100, as shown in fig. 9, there are two autocorrelation results exceeding the threshold 100, but the autocorrelation result at the 25 position is selected as the peak value of the current operation, and the position at the 25 position is taken as the position of the found LAS code.

Prior preferred training symbol format 0]_SN,[X_las]_SN,[0]_SN,[X_las]_SN,[X_las]_LN,[X_las]_LNIn the case of (2), there are two LAS short codes in the training sequence. At this time, two peaks exceeding the threshold can be found out by the sliding window autocorrelation calculation method. Fig. 9 shows a distribution diagram of the autocorrelation result in which two peaks exist. At this time, it is necessary to determine which one is the peak of the preceding short code and which one is the peak of the succeeding short code.

Fig. 10 shows a schematic diagram of the training sequence in the case where two peaks are detected. Two training sequences for repeated cyclic transmission are shown in fig. 10. The length of the received signal spans two training sequences, and thus, one of the two peaks found may be due to the first LAS short code of the next training sequence. It is necessary to determine which LAS short code corresponds to each peak.

Specifically, if the interval length between two peaks is 2 × SN, the first peak exceeding the threshold is selected as the start position of the first short LAS code, and if the interval length between two peaks is greater than 2 × SN, the second peak exceeding the threshold is selected as the start position of the first short LAS code.

If there is a multipath channel, two parts of concentrated distribution correlation peaks appear after the sliding window, the correlation peak of each part is compared with the threshold value respectively, the first peak value point of the threshold value is selected, two points exceeding the threshold value are obtained after the two parts are compared, and then the position corresponding to the LAS code is determined according to the method.

In addition, if the transmission signal passes through other band-limiting filters, the matched filtering is performed by smooth peaks instead of independent points, so that a peak value point needs to be selected according to an actual band-limiting filter.

Fig. 11 illustrates a block diagram of a timing synchronization unit of a receiving end in accordance with an aspect of the invention. The timing synchronization unit may be part of the synchronization unit discussed above in connection with fig. 2 and 5.

As shown in fig. 11, the timing synchronization unit 1100 may include an autocorrelation calculation unit 1110 for performing autocorrelation calculation. The autocorrelation calculating unit 1110 may perform windowing on the received signal, perform autocorrelation calculation on the signal within the window using the local LAS code, and slide the window to perform the next autocorrelation calculation until the signal reception length is reached. The timing synchronization unit 1100 may further include a peak determining unit 1120 for determining a position of a peak from the obtained correlation result set to find a start position of the LAS code. The peak determining unit 1120 may select a suitable threshold, and use the autocorrelation result exceeding the threshold as the peak.

Fig. 12 illustrates a flow diagram of a timing synchronization method in accordance with an aspect of the subject invention. As shown, the method may include:

step 1201: taking a window from the received signal, performing autocorrelation calculation on the signal in the window by using a local LAS code, and sliding the window to perform the next autocorrelation calculation until the signal receiving length is reached; and

step 1202: the position of the peak is judged according to the obtained correlation result set to find the start position of the LAS code.

As described above, in the case where there are two LAS short codes, if the two peak interval lengths are 2 SN, the first peak exceeding the threshold is selected as the start position of the first short LAS code, and if the two interval lengths are greater than 2 SN, the second peak exceeding the threshold is selected as the start position of the first short LAS code.

Carrier synchronization procedure

After receiving the signal, the signal needs to keep synchronization with the communication system, including timing synchronization and carrier synchronization, the received signal and the system keep time synchronization, the initial position of the LAS code is obtained through timing synchronization, and then frequency synchronization is performed.

For carrier synchronization, the training sequence information portion of the received signal includes at least one pair of identical LAS codes. And performing cross-correlation operation on the repeated LAS codes to obtain the frequency deviation delta f.

Assuming that the carrier offset between the receiver and the transmitter is Δ f and the AD sampling interval is T, when the receiving end ignores the influence of the noise signal, the received signal is expressed as:

y_n＝x_ne^j2πΔfnT

the correlation coefficients of the two last LAS codes are:

where L denotes an interval between LAS codes.

From the above equation, the carrier frequency offset is:

preferably, the training sequence information part may include two pairs of LAS codes, wherein a same pair of LAS codes is an LAS short code, whereby carrier coarse synchronization may be performed first; and in addition, a pair of identical LAS long codes is included, so that fine carrier synchronization can be carried out.

After the timing synchronization is finished, two corresponding short LAS codes can be extracted according to the training symbol index returned by the timing synchronization, the short LAS codes are subjected to carrier coarse synchronization, the short codes can process larger frequency deviation, and the estimated frequency deviation value is calculated according to the formula and is delta f₁. Then two parts of long LAS codes are extracted, carrier fine frequency offset correction is carried out on the long LAS codes, and the estimated frequency offset value delta f is obtained₂Referring to the frequency offset of coarse synchronization, the final output frequency offset is Δ f ═ Δ f₁+Δf₂。

In the previously preferred training symbol format [0 ]]_SN,[X_las]_SN,[0]_SN,[X_las]_SN,[X_las]_LN,[X_las]_LNFor example. Let LN be 272 and SN be 27224, the total length of the training symbols is 640. The two short LASs are at two positions (25:48) and (73:96), respectively, and the long LAS code is at two positions (97:368) and (369: 640), respectively.

Ideally, the start position of the LAS code obtained by the timing synchronization calculation is the start position of the first short LAS code, which is 25. And correspondingly extracting corresponding codes from the received signals according to the indexes and the code lengths LN and SN of the long and short codes.

Coarse carrier synchronization

Two part short LAS codes are extracted from the received signal according to a formula

And (4) performing conjugate multiplication on the correlation coefficient to obtain a correlation coefficient R. According to the formula

Finding the corresponding coarse frequency deviation Deltaf₁Where L denotes the interval between two short LAS codes, as can be seen from the training symbol structure, L-2 SN-48.

According to the calculated coarse frequency deviation passing formula

And carrying out frequency offset correction on the received signal to obtain a signal after the first frequency offset correction.

Carrier fine frequency offset correction

Carrying out coarse frequency deviation correction on the received signal in the carrier coarse synchronization to obtain a received signal y_n'. The fine frequency offset process is from y_n' two-part long LAS code is extracted according to the formula

Finding the corresponding fine frequency deviation Deltaf₂L denotes the spacing between two long LAS codes, which may be represented by a training symbol structureAs can be seen, L-LN-272.

Referring to the frequency offset of the coarse synchronization, the final output frequency offset is Δ f ═ Δ f₁+Δf₂. And according to formula y_n”＝y_n'e^j2 ^π(-Δf)nTAnd solving the signal after the fine frequency offset correction of the received signal.

The signal y after twice frequency deviation correction_n"as input signal to the channel estimation process, the carrier synchronization process ends.

Fig. 13 shows a block diagram of a carrier synchronization unit 1300. The carrier synchronization unit 1300 may be part of the synchronization unit discussed above in connection with fig. 2 and 5.

As shown, the carrier synchronization unit 1300 may include a cross-correlation calculation unit 1310 and a frequency correction unit 1320. The cross-correlation calculation unit 1310 may perform a cross-correlation calculation on a pair of LAS codes to obtain a frequency offset of a carrier between a receiving end and a transmitting end. The frequency correction unit 1320 may perform frequency offset correction on the received signal according to the frequency offset of the carrier.

In an embodiment, the cross-correlation calculation unit 1310 may first perform a cross-correlation calculation of a pair of LAS short codes to obtain a coarse frequency offset of a carrier between a receiving end and a transmitting end. The frequency correction unit 1320 may perform a first time frequency offset correction on the received signal according to the coarse frequency offset. The cross-correlation calculation unit 1310 performs cross-correlation calculation on a pair of LAS long codes extracted from the received signal subjected to the primary frequency offset correction to obtain a fine frequency offset of a carrier between the receiving end and the transmitting end. The frequency correction unit 1320 may perform secondary frequency offset correction on the received signal after the primary frequency offset correction according to the fine frequency offset and the coarse frequency offset, so as to obtain a final frequency offset-corrected signal.

Fig. 14 shows a flow chart of a carrier synchronization method according to an embodiment. As shown, the carrier synchronization method may include the following steps:

step 1401: performing cross-correlation on two LAS codes extracted from a received signal to obtain a frequency offset of a carrier between a receiving end and a transmitting end; and

step 1402: a frequency offset correction is performed on the received signal based on the frequency offset.

Fig. 15 shows a flowchart of a carrier synchronization method according to another embodiment. As shown, the carrier synchronization method may include the following steps:

step 1501: performing cross-correlation on two LAS short codes extracted from a received signal to obtain a coarse frequency offset of a carrier between a receiving end and a transmitting end;

step 1502: performing primary frequency offset correction on the received signal according to the coarse frequency offset;

step 1503: performing a cross-correlation calculation on a pair of LAS long codes extracted from the primary frequency offset corrected received signal to obtain a fine frequency offset of a carrier between a receiving end and a transmitting end; and

step 1504: and performing secondary frequency offset correction on the received signal subjected to the primary frequency offset correction according to the fine frequency offset and the coarse frequency offset.

While, for purposes of simplicity of explanation, the methodologies are shown and described as a series of acts, it is to be understood and appreciated that the methodologies are not limited by the order of acts, as some acts may, in accordance with one or more embodiments, occur in different orders and/or concurrently with other acts from that shown and described herein or not shown and described herein, as would be understood by one skilled in the art.

Channel estimation procedure

Channel estimation is used to estimate the transmission characteristics of the channel, i.e. the effect of the channel on the transmitted signal. By using training symbols known to both the transmitting end and the receiving end, the receiving end can perform channel estimation based on the known training symbols and the received training symbols. For example, the receiving end may perform correlation on known training symbols and received training symbols to determine the transmission characteristics of the channel. After performing channel estimation, the receiving end can demodulate the received unknown data signal using the determined channel estimation to determine the actual data signal transmitted by the transmitting end.

The received signal is subjected to timing synchronization and the system maintains time synchronization. Then, the carrier synchronization is carried out with the received signal, the carrier synchronization comprises coarse synchronization and fine synchronization, and the carrier synchronization is obtained through synchronizationCarrier frequency deviation delta f of a receiver and a transmitter is obtained, and the received signal is corrected through the carrier frequency deviation to obtain a corrected received signal y_fixTo y for_fixAnd (6) channel estimation is carried out.

The present invention utilizes the LAS code as a training sequence, e.g., the long LAS code L-LAS in the training symbol format may be used for channel estimation.

The channel estimate may be expressed as:

wherein y is_nRepresenting the received signal after carrier-synchronous correction, i.e. y_fix. N denotes the LAS code length. x is the number of_nRepresenting local LAS codes, i.e. x_nRepresented as one of the last two long LAS codes in the training symbols. R₀Denotes the sum of squares of the LAS code and P denotes the number of multipath channels.

Channel estimator receives signal y from training symbol_fixThen, an inverse channel system is constructed according to the estimated h (t), and the received data signal is restored to the estimation of the signal fed to the channel by the sending end after passing through the inverse channel system.

General received signal y_nCan be expressed as

e_nRepresenting noise. After the formula is substituted into the formula and expanded, the following formula is obtained:

the autocorrelation of the training sequence is represented, and the estimated channel height is close to the real channel by reasonably designing the autocorrelation coefficient to be zero, so that the accuracy of channel estimation is greatly improved. According to the invention, since LAThe probability of 0 occurrence in the S code autocorrelation is extremely high, so that the success rate of channel estimation is greatly improved when the channel estimation is carried out.

The field generally uses M sequences for channel estimation. The autocorrelation characteristic of the M sequence is shown in fig. 7, and it can be seen from the figure that pulses appear at certain time intervals in the autocorrelation characteristic, the autocorrelation characteristic is not good, and the channel estimation formula corresponds to

In (1)

The probability that the value is not 0 is very high, so the deviation between the estimated channel model and the ideal channel model is large, the subsequent decoding processing is greatly influenced, and the error rate of the system is improved.

Compared with an LAS code sequence, the method has the characteristics that the autocorrelation function is an ideal impact function at the origin, the position outside the origin is zero, and the position of the cross-correlation function is zero, so that the actually estimated channel model and the ideal model have small deviation when channel estimation is carried out, the error rate of a system is reduced, and the performance of the system is well improved.

According to the invention, because the number of the long LAS codes in the training symbols is two, the channel estimation process can be realized by adopting any one of the long LAS codes, or the two long LAS codes can be subjected to two times of channel estimation, thereby improving the success rate of channel estimation.

There may be one channel or a multipath channel in a communication environment, and a receiver may determine whether the multipath channel exists according to the environment. In the case of no multipath channel, i.e. p is 0, the channel estimate h can be calculated directly from the above equation. Under the condition of multipath channel, the channel estimation value h of each multipath path can be respectively calculated according to the formula_pWhere a local LAS code x is applied for each multipath path_nThe offset is performed and the deviation of each path may be 1.

For example, the actual multipath channel may be, for example, 6. First, the local LAS codes are arranged into 6 columns according to the number of multipaths, the deviation of each column path is 1, and the arrangement is shown in fig. 16.

According to training symbol format [0 ]]_SN,[X_las]_SN,[0]_SN,[X_las]_SN,[X_las]_LN,[X_las]_LNFrom the correction signal y_fixFinds the corresponding LAS code position in and extracts as y_fix-lasTwo parts in total.

Will extract y_fix-lasRespectively making said codes pass through the formula with the local LAS codes of 6 rearranged multipath channels

After processing, obtaining the channel estimation value h of each multipath path_p. Because two parts of LAS codes can be used for channel estimation, each part can obtain channel estimation value h after being processed_pAveraging the two parts to obtain the final channel estimation value h of each multipath path_p。

The channel estimate h may then be based on each multipath path_pTo demodulate the received data signal and thereby recover the transmit end signal for each multipath path.

Designing training sequence bandwidth

The design symbol structure in the system comprises a training sequence TSC (training sequence code) and data (data). The design of the training symbols is crucial, and affects three most important links of timing, synchronization and channel estimation of the whole system, if any one of the three steps has a large error, the influence on the whole system is large, and the subsequent decoding process is not meaningful.

The design process of the frequency width of the training sequence is complex, the corresponding power spectrum density is large when the frequency width is short, the receiving and the sending of data can be influenced when a plurality of carriers exist in the system, and the corresponding power spectrum density is too small when the frequency width is too large, so that the requirement on the sensitivity of a transmitter and a receiver of the system is extremely high.

In the existing communication system, the method of the same bandwidth of the training sequence and the data is generally adopted, the corresponding power spectral densities are the same, and because the bandwidth in the general system is shorter, the time domain transmission time is longer, the signal synchronization and channel estimation processing time processes are influenced, the waiting time of the subsequent decoding process is also longer, and the transmission rate of the system is reduced. In addition, since the training sequence transmission time is long, when a signal is sampled, the sampling rate is low, the time resolution is not fine enough, and the bias of channel estimation is affected.

The present invention makes the bandwidth of the training sequence much larger than the bandwidth of the data (for example, 5 times, 10 times, 15 times or more), so that the power spectral density of the training sequence is lower than the power spectral density of the data, and the relationship between the training sequence, the bandwidth of the data and the power spectral density is shown in fig. 17. Since the transmission power of the training sequence and the data needs to be kept consistent, it can be seen from the figure that when the bandwidth of the training sequence is widened, the corresponding power spectral density is also greatly reduced, which is very low relative to the data power spectral density.

The system can use all available spreading codes, including m-sequence, Golomb code, CAN (cyclic Algorithm New), and LAS code. In the system, the processing procedures of timing synchronization, carrier synchronization and channel estimation are described by taking LAS codes with perfect complementary orthogonality as an example. Therefore, all the methods and apparatuses for timing synchronization, carrier synchronization, and channel estimation using the LAS code as the training code described above are also applicable to timing synchronization, carrier synchronization, and training estimation using all suitable spreading codes as the training codes. Therefore, the timing synchronization, carrier synchronization and channel estimation algorithms illustrated above with respect to the LAS code are shown by way of example only, and the above description of the invention applies to all suitable training codes.

The characteristic of LAS-codes is that the autocorrelation function is an ideal impulse function at the origin, zero everywhere outside the origin, and the cross-correlation function is zero everywhere, the autocorrelation characteristics of LAS-codes are shown in fig. 8. And therefore do not interfere with each other when the training sequences overlap. The design can improve the spectrum utilization rate and the transmission rate of the system.

By the formula

It can be known that, when the frequency domain bandwidth is larger, the time corresponding to the frequency domain bandwidth is smaller, i.e. the transmission and reception process of the training sequence can be completed in a shorter time. In the signal receiving process, for the data with the same length, when the receiving time is shortened, the sampling rate of the signal can be improved, and the time resolution is finer. The accuracy of time resolution is improved in the channel estimation process, so that the channel estimation result is more accurate.

In one aspect, the training sequence and the data can be transmitted superimposed at the same time, since the power spectral density of the training sequence is very low and has little effect on the data signal. In other words, the training sequence and the data are transmitted at least partially overlapping in frequency and/or time. When there are two carrier signals simultaneously transmitting data, the structural diagram is shown in fig. 18, and it can be seen from the diagram that there is a guard band in the middle of the actual data carried by the two carriers, so that there is no overlapping and no mutual interference; the frequency width of the training sequence is overlapped with the actual data, and the power spectral density of the training sequence is very low, so that the actual data cannot be interfered; furthermore, different training sequences can be distinguished by different spreading codes, and no confusion is caused. The training sequence does not occupy specific frequency and time resources, and the frequency spectrum utilization rate and the transmission rate of the system are improved.

In one embodiment, the system may use a LAS code with perfect complementary orthogonality as a training sequence, and is characterized in that the autocorrelation function is an ideal impulse function at the origin, is zero everywhere outside the origin, and the cross-correlation function is zero everywhere, and the autocorrelation and cross-correlation characteristics of the LAS code are shown in fig. 5. And therefore do not interfere with each other when the training sequences overlap. The design can improve the spectrum utilization rate and the transmission rate of the system.

In this case, we design the format of the training sequence as: [0]_SN,[X_las]_SN,[0]_SN,[X_las]_SN,[X_las]_LN,[X_las]_LN。

Those of skill in the art would understand that information, signals, and data may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits (bits), symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The various illustrative logical modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

In one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software as a computer program product, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a web site, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, Digital Subscriber Line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk (disk) and disc (disc), as used herein, includes Compact Disc (CD), laser disc, optical disc, Digital Versatile Disc (DVD), floppy disk and blu-ray disc where disks (disks) usually reproduce data magnetically, while discs (discs) reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A carrier synchronization method, comprising:

performing cross-correlation operation on two LAS codes extracted from a received signal to obtain frequency offset of a carrier between a receiving end and a transmitting end, wherein the received signal is a time domain signal from the transmitting end and includes a training sequence based on the LAS codes, the training sequence includes two LAS short codes and two LAS long codes, performing cross-correlation operation on the two LAS codes extracted from the received signal to obtain frequency offset of the carrier between the receiving end and the transmitting end includes:

performing a cross-correlation operation on the two LAS short codes extracted from the received signal to obtain a coarse frequency offset of a carrier between a receiving end and a transmitting end; and

performing a cross-correlation operation on the two LAS long codes extracted from the received signal subjected to the primary frequency offset correction to obtain a fine frequency offset of a carrier between a receiving end and a transmitting end; and

performing frequency offset correction on the received signal based on the frequency offset, comprising:

performing the primary frequency offset correction on the received signal based on the coarse frequency offset; and

performing secondary frequency offset correction on the received signal subjected to the primary frequency offset correction based on the coarse frequency offset and the fine frequency offset,

the performing, based on the coarse frequency offset and the fine frequency offset, a secondary frequency offset correction on the received signal subjected to the primary frequency offset correction includes:

performing the secondary frequency offset correction on the primarily frequency offset-corrected received signal based on the sum of the coarse frequency offset and the fine frequency offset,

the training sequence comprises [0 ]]_SN,[X_las]_SN,[0]_SN,[X_las]_SN,[X_las]_LN,[X_las]_LNWherein [0 ]]_SNIs a 0 sequence with length SN, and the LAS short code is [ X_las]_SNSN is the length of the LAS short code, the LAS long code is [ X ]_las]_LNAnd LN is the length of the LAS long code.

2. The carrier synchronization method of claim 1, wherein the two LAS short codes are also used for timing synchronization, the two LAS short codes and extraction positions of the two LAS long codes being determined based on a result of timing synchronization.

3. A carrier synchronization apparatus, comprising:

a cross-correlation calculation unit for performing a cross-correlation operation on two LAS codes extracted from a received signal to obtain a frequency offset of a carrier between a receiving end and a transmitting end, wherein the received signal is a time domain signal from the transmitting end and includes a training sequence based on the LAS codes, the training sequence includes two LAS short codes and two LAS long codes, the performing a cross-correlation operation on two LAS codes extracted from the received signal to obtain a frequency offset of a carrier between the receiving end and the transmitting end includes:

a frequency correction unit configured to perform frequency offset correction on the received signal based on the frequency offset, including:

the frequency correction unit is further configured to perform the secondary frequency offset correction on the received signal subjected to the primary frequency offset correction based on the sum of the coarse frequency offset and the fine frequency offset,

4. The carrier synchronization apparatus of claim 3, wherein the two LAS short codes are also used for timing synchronization, the two LAS short codes and extraction positions of the two LAS long codes being determined based on a result of timing synchronization.