CN106656453A - Synchronous device and method in narrowband wireless communication terminal - Google Patents

Abstract

The invention discloses a synchronous detection device applied to a narrow-band wireless communication system terminal, which includes a down-sampling module, a sliding autocorrelation module and a differential cross-correlation module. The down-sampling module down-samples the received 1.92MHz time-domain signal into a 240kHz signal according to the OFDM symbol duration and a fixed down-sampling pattern. The sliding autocorrelation module moves the sampling point data bit by bit within the 10ms wireless frame processing window length as the starting position t, and uses the length of 11 OFDM symbols as the sliding window, and separates the 11 groups of sampling points in the sliding window into two groups Correlation accumulation between them. The differential cross-correlation module divides the obtained preliminary synchronization sequence into two parts that are approximately equal, and performs cross-correlation accumulation with the locally generated main synchronization sequence. The synchronous detection device disclosed in the present invention can still detect the main synchronous signal preferably in the application scenario of a narrowband wireless communication system with a low signal-to-noise ratio and a large frequency offset, and its implementation complexity is low, satisfying the Low-cost requirements for narrowband wireless communication terminals.

Description

Synchronization device and method in narrowband wireless communication terminal

technical field

The present invention relates to the field of mobile communication, in particular to a synchronization device and method applied to narrowband cellular communication terminals in a future Internet of Things network.

Background technique

In the recent communication market, IoT (Internet of Things) has become a bright spot in the industry, and many operators and devices have demonstrated their latest innovations and application cases. Among them, narrowband wireless communication technology (NB-Iot) is the key for operators to enter the Internet of Things market. The narrowband wireless communication system has the advantages of low power consumption, wide coverage, low cost, and large capacity, so it can be widely used in a variety of vertical industries, such as remote meter reading, asset tracking, smart parking, smart agriculture, etc. The first version of the 3GPP standard is expected to be released in June 2016. It is expected that narrowband wireless communication will stand out from multiple technical competitions in the LPWA market and become the best choice for leading operators.

The first version of narrowband wireless communication supports 3 operating modes (standalone, in-band, guard-band), including:

■ Standalone: Use the frequency spectrum of the existing GERAN system to replace one or more GSM carriers

■ Guard-band: Utilize unused resource blocks within the LTE carrier guard interval

■ In-band: Utilize resource blocks within common LTE carriers.

In the network deployment of narrowband wireless communication, the bandwidth resources available to the base station are wide, but for a specific narrowband wireless communication terminal equipment, its uplink and downlink bandwidth only occupy a maximum of 180kHz (that is, one PRB). When the traditional LTE shared bandwidth is deployed, the downlink synchronization pilot of the narrowband wireless communication system can only be sent on specific PRBs. The difference between these specific PRBs and the 100 kHz grid point is fixed at 2.5 kHz or 7.5 kHz, called anchor PRBs .

The downlink synchronization pilot of the narrowband wireless communication system includes primary and secondary synchronization pilots. The primary synchronization signal is used to obtain time and frequency domain synchronization of the network, and the secondary synchronization signal is used to determine the cell ID. The technical solution involved in the present invention is Detection of the primary synchronization sequence for narrowband wireless communication systems. The characteristics of the Primary Synchronization Pilot (NPSS) in the narrowband wireless communication system of the first version of 3gpp include:

■The NPSS transmission period is a wireless frame length (10ms)

■NPSS uses the last 11 OFDM symbols of subframe 5 in each radio frame, and occupies 11 subcarriers on each symbol for transmission, from subcarrier 0 to subcarrier 10

■NPSS uses the same ZC sequence as the base sequence in each OFDM symbol, and the ZC root sequence is u=5, which is generated in the frequency domain. The ZC sequence has good time domain and frequency domain correlation

■ NPSS uses random pattern binary scrambling sequences between different OFDM symbols.

Since the terminal equipment of narrowband wireless communication must have the characteristics of low cost, the precision of the crystal oscillator is low, so it brings a large initial frequency offset. In addition, as mentioned above, in the same network deployment mode as the traditional LTE, the downlink synchronization of the narrowband wireless communication system There is a frequency offset of 2.5/7.5kHz between the anchor PRB where the pilot is located and the 100kHz scanning grid. The superposition of the two factors leads to an initial frequency offset of more than 25kHz at most when the narrowband wireless communication terminal equipment is initially synchronized. .

Moreover, narrowband wireless communication terminal equipment is often deployed in an extremely low SNR network environment, and how to detect synchronization signals in a strong noise background is also a technical problem that needs to be overcome.

The primary synchronization detection method in the traditional LTE system, such as the invention with the application number 20101038021 "A 3GPP LTE downlink initial primary synchronization detection method", or the invention with the application number 2013103796348 "A fast downlink method for TD-LTE cell handover Master Synchronization Method", and the invention with application number 201010111963 "A Method and Device for LTE Master Synchronization Signal Detection and Sequence Generation in LTE System", which discloses the cross-correlation of the received sequence with the locally generated sequence The method to detect (or determine) the existence of synchronization signals. For narrowband wireless communication systems, since the synchronization sequence is short and works in an environment with extremely low signal-to-noise ratio and large initial frequency offset, it is fundamental to apply the synchronization sequence detection method of cross-correlation of frequency domain data used in traditional LTE systems Unable to find relevant peaks.

Contents of the invention

In view of the above defects and deficiencies in the prior art, the purpose of the present invention is to provide a synchronization device and method applied to narrowband cellular communication terminals of the Internet of Things, which can still be synchronized in the environment of extremely low signal-to-noise ratio and large frequency deviation. The detection of the main synchronization signal can be better realized, and its realization cost is relatively low.

According to one aspect of the present invention, a synchronization device for a narrowband cellular communication terminal is provided, including the following modules, as shown in FIG. 1 .

The M101 down-sampling module is used for down-sampling the time-domain sampling signal with a sampling rate of 1.92MHz to a 240kHz signal.

The downsampling module divides 1920 sampling points per 1 ms (one subframe length) into 14 OFDM symbol durations, and the downsampling patterns in the first and seventh OFDM symbol durations are {10,8,8,8, 8,8,8,8,8,8,8,8,8,8,8,8,8}, the downsampling pattern in other OFDM symbol lengths is {9,8,8,8,8,8, 8,8,8,8,8,8,8,8,8,8,8}.

The M201 sliding autocorrelation module is used to initially determine the existence and preliminary position of the main synchronous sequence.

The sliding autocorrelation module also includes a data buffer, which caches the downsampled data of the last 11 OFDM durations of the last 10ms wireless frame, so the total data length processed by the sliding autocorrelation module at one time is the current 10ms wireless frame and the previous one. The sum of the last 11 OFDM symbols of a 10ms radio frame.

The sliding autocorrelation module moves the sampling point data in the processing window bit by bit as the starting position t, and takes out the down-sampled data whose duration is 11 OFDM symbols as a sliding window, and then takes the sampling point in the sliding window It is divided into 11 groups, and the sampling points between the two groups are multiplied by the corresponding scrambling sequence, and the correlation accumulation is performed, and the alpha filtering is performed on the multiple sets of sliding autocorrelation results of multiple 10ms wireless frame processing windows, and finally each sliding window The sliding autocorrelation results were normalized by power.

If the sliding autocorrelation result of a sliding window is greater than the threshold value of the preset value, the differential cross-correlation module is started.

Further, the sliding autocorrelation module also includes a fractional multiple frequency offset estimation and calibration sub-module, which performs fractional multiple frequency offset estimation and calibration according to the phase value of the obtained sliding autocorrelation result, and the fractional multiple The frequency offset estimation is estimated according to the following formula,

Among them, arctan{A _t } means to take the phase value of the sliding autocorrelation result, 1.92MHz is the sampling rate of the initial time domain data, and 137 is the number of sampling points of an OFDM symbol duration.

The M301 differential cross-correlation module is used to further determine whether there is an NPSS signal.

The processing data object of the differential cross-correlation module is a sampling sequence of 187 points in a sliding window obtained from the sliding autocorrelation module, and the difference of the 187-point sampling sequence is divided into two sections of approximately equal length, for example, the first One section has a length of 97 points, and the second section has a length of 98 points, or, the first section has a length of 98 points, and the second section has a length of 97 points. After the yoke multiplication and accumulation, the results of the two sections are correlated and combined, and if the correlated combined result is greater than the preset threshold value, it is confirmed that the NPSS exists.

Further, the correlation merging also includes performing power normalization on the merging results in each 10ms radio frame.

Preferably, the differential correlation module also includes a submodule for performing integer multiple frequency offset estimation and calibration on the received sequence, and the integer multiple frequency offset estimation and calibration submodule enumerates all possible frequency offsets within the frequency offset range. Integer multiplication frequency offset value, try each of the integer multiplication frequency offset values to modulate the locally generated NPSS time-domain sequence, and use the modulated local NPSS sequence for differential correlation to find the maximum value of the differential cross-correlation result , and its corresponding integer multiple frequency offset value is the estimated value. Then, the sum of the estimated fractional multiple frequency offset and the integer multiple frequency offset estimate is integrated into the total frequency offset estimate, and the phase calibration is performed according to the sampling time of the sampling point.

More preferably, the submodule of timing estimation is also included in the differential correlation module, that is, the local NPSS time domain sequence with a high sampling rate is generated first, and then different initial sampling point offsets are tried and down-sampled to generate the The local NPSS time-domain sequence is then subjected to the differential cross-correlation, and an initial offset value that maximizes the differential cross-correlation value is found as an estimated timing offset.

The beneficial effect of the device of the present invention is that it provides a solution for the narrowband wireless communication terminal to correctly detect the primary synchronization sequence in the environment of low signal-to-noise ratio and large initial frequency offset, which is different from the traditional method of correlating the received signal with the local sequence The scheme provided by the present invention has better performance, because the scheme of the present invention can obtain the combination gain between multiple 10ms wireless frames by sampling, and in specific engineering practice, a longer synchronization time can be exchanged for synchronous access Accuracy, so it is suitable for the performance requirements of narrowband wireless communication with low delay sensitivity and high harsh environment access. Under the optimal configuration, the device disclosed in the present invention also performs estimation and calibration of frequency offsets of fractional multiples and integer multiples during the process of detecting NPSS signals, which further improves the performance of resisting large frequency offsets. Under a more optimal configuration, the device disclosed in the present invention can also perform preliminary timing estimation, which creates better conditions for subsequent downlink data reception and improves the overall performance of the receiver. The device of the present invention has been subjected to multiple simulation experiments and evaluations. According to the 3gpp protocol agreement, according to the simulation configuration agreed by 3gpp, the detection success rate of more than 95% can be obtained by using the device disclosed in the invention, and the timing can be achieved under the optimal configuration. The synchronization is within 4T _samp (where T _samp corresponds to 1.92MHz sampling interval), and the frequency synchronization error is within 50Hz.

According to another aspect of the present invention, a synchronization detection method for a narrowband cellular communication terminal is provided, which includes the following processes.

S101 down-sampling process, the time-domain signal with a sampling rate of 1.92MHz is taken as a unit length of OFDM symbols, and is down-sampled to a signal with a sampling rate of 240kHz according to a fixed down-sampling pattern; the fixed down-sampling pattern is as described in the device part of the present invention .

S201 Sliding autocorrelation process, move the sampling point data in the 10ms wireless frame processing window bit by bit as the starting position t, and use the length of 11 OFDM symbols as the sliding window, divide the sampling points in the sliding window into There are 11 groups, and the sampling points between the two groups are correlated and accumulated.

Preferably, the sliding autocorrelation process further includes a sub-process of estimating and calibrating the fractional multiple frequency offset according to the autocorrelation result.

If the sliding autocorrelation calculated by the sliding autocorrelation process is greater than the threshold value, the differential cross-correlation process is started.

S301 Differential cross-correlation process, dividing the synchronous sequence in the sliding window obtained by the sliding autocorrelation process into two parts of equal length, and performing cross-correlation accumulation with the locally generated synchronous sequence.

Preferably, the differential cross-correlation process further includes a sub-process of estimating and calibrating integer multiple frequency offsets.

More preferably, the differential cross-correlation process further includes a timing estimation sub-process.

If the cross-correlation result obtained by the differential cross-correlation process is greater than the threshold value, it is confirmed that the detected sequence is the primary synchronization sequence.

Description of drawings

FIG. 1 is a schematic diagram of a module structure of a synchronization device involved in the present invention.

FIG. 2 is a schematic diagram of a downsampling pattern.

FIG. 3 is a schematic diagram of a control relationship between actual subframe sampling points and sampling patterns within a time length of 1 ms randomly selected in practice.

Figure 4 is a schematic diagram of the physical mapping of NPSS sequences.

Fig. 5 is a schematic diagram of the comparison between the 10ms processing window existing in practice and the actual wireless frame position.

Figure 6 is a schematic diagram of sliding autocorrelation.

FIG. 7 is a schematic diagram of trying different timing offsets in timing estimation.

detailed description

The implementation of the present invention will be described below through specific examples. The specific examples described here are only used to explain the present invention, but are not intended to limit the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

Please refer to the accompanying drawings, the modules contained in the NPSS detection device are shown in Figure 1, including a downsampling module, a sliding autocorrelation module (AutoCorr), a rough cross-correlation module and a fine cross-correlation module.

M101 Downsampling Module

The downsampling module realizes downsampling from a sampling rate of 1.92MHz to 240K. Before downsampling, each subframe inputs 1920=(137*14+2) sampling points of 1ms, and after downsampling, each subframe outputs 238=(17* 14) sampling points, and follow the fixed downsampling pattern below:

The 1920 sampling points of each subframe are recorded as 14 groups (14 OFDM symbols), the sampling points of the first group are 138, the sampling points of the 2-6 groups are 137, and the sampling points of the 7th group are 138 There are 137 sampling points in groups 8-14. Groups 1-6 are marked as slot 1 (slot1), groups 7-14 are marked as slot 2 (slot2), the first group of each slot is marked as the first OFDM symbol, and the remaining groups are marked as non- The first OFDM symbol.

The downsampling pattern of the first OFDM symbol (i.e. group 1 and 7) of each slot is {10,8,8,8,8,8,8,8,8,8,8,8,8,8 ,8,8,8}; as shown in the upper part of Figure 2, first down-sample one point every 10 points, down-sample one point every eight points for the remaining sampling points, and so on.

The non-first OFDM symbol (ie group 2-6, group 8-14) sampling pattern is {9,8,8,8,8,8,8,8,8,8,8,8,8,8 ,8,8,8}; As shown in the lower part of Figure 2, first down-sample one point every nine points, down-sample one point every eight points for the remaining sampling points, and so on.

In this way, the number of down-sampled points of each OFDM symbol is 17 points, and the number of sampling points included in each 1ms duration is 238=(17*14).

Figure 3 shows the comparison relationship between the actual subframe sampling point and the sampling pattern within the random sampling time length of 1 ms in practice, assuming that the starting position of the randomly selected 1 ms time window corresponds to the last OFDM symbol of the previous sub-frame, The sampling pattern of the first group is {10,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8}, so it corresponds to the subframe The first 17 downsampled data are the 1st point in the original CP segment, the 2nd, 10th, ..., 122nd points in the data segment, and the next downsampling window corresponds to the first OFDM symbol of this subframe, The sampling pattern is {9,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8}, so it corresponds to 17 in the subframe after downsampling The first data is the 3rd point in the original CP segment, the 1st, 9th, ..., 122nd points in the data segment, the third downsampling window corresponds to the second OFDM symbol of this subframe, and the sampling pattern is still { 9,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8}, so the 17 data corresponding to the downsampling in the subframe are the original The 2nd point in the CP segment, the 1st, 9th, ..., 122nd points in the data segment, and so on.

It can be seen that, using the above fixed sampling pattern for downsampling can ensure that the number of points after downsampling in each OFDM symbol time length is the same, and ensure that the error between sampling positions after downsampling of the original OFDM symbol remains at a maximum of 1 sampling points, most of the OFDM sampling positions are error-free, which on the one hand reduces the calculation amount of subsequent sliding autocorrelation, and at the same time minimizes the performance degradation caused by downsampling to sliding autocorrelation.

M201 Sliding Autocorrelation Module

As shown in Figure 4, as stipulated in the protocol [36.211], the primary synchronization code NB-PSS sequence of the narrowband wireless communication system is a short sequence in the frequency domain, occupying 11 REs in the frequency domain and 11 consecutive REs in the time domain The OFDM symbols are sent after being scrambled.

After downsampling, the number of sampling points in 1ms is 238. The primary processing object of the sliding autocorrelation module is the received time domain data within the window time of each wireless frame (10ms). The actual sliding autocorrelation module also includes a data buffer. The data of the last 11 OFDM matches in the last wireless frame window, that is, 11*17 sampling points, therefore, the actual one-time processing object of the sliding autocorrelation module includes 2380 sampling points + 11*17 downsampling of a wireless frame after downsampling Sampling points, the data of a total of 2567 downsampling points.

The beneficial effect of increasing the data buffer in the sliding autocorrelation module is to prevent missing data detection, as shown in Figure 5, a possible scenario is that the starting position of the current 10ms processing window is just inside the frame that actually sends the NPSS subframe, The addition of 11 OFDM symbol duration data buffers can ensure that at least one complete NPSS sequence must be stored in the increased sliding autocorrelation processing window.

As shown in Figure 6, the sampling point data in the processing window is moved bit by bit as the starting position t, and the sampling point is taken from the time window with a length of 11 OFDM symbols (that is, 187 sampling points) as a sliding window .

Then divide the 187 sampling points in a sliding window into 11 groups, with 17 sampling points in each group. As shown in Figure 6, the sampling points between the two groups are correlated and accumulated, and each OFDM needs to be multiplied in the correlation accumulation. The scrambling sequence of symbols, as shown in the following formula,

In the above formula, , is the received sampling point sequence of the m-th OFDM symbol duration from the t-th sampling point, s _m and s _m+1 are the scrambling codes corresponding to the two OFDM symbol sequences, and * means that each Take the conjugate operation.

Preferably, in engineering practice, it also includes an alpha filter operation on the autocorrelation results on the continuous wireless frame (10ms) window

Thereby, a diversity combining gain is obtained, and the accuracy of detection is further improved.

Then, the sliding correlation results are power normalized,

Judging whether the normalized sliding autocorrelation result is greater than the predefined threshold value, if it is greater than, it is considered that the wireless frame window contains NPSS, and the approximate starting position is at the tth sampling point, and it is transferred to the next coarse cross-correlation module, otherwise go to the judgment of the next wireless frame window.

Preferably in engineering, it also includes estimating and calibrating the fractional multiple frequency offset of the downsampled signal according to the sliding autocorrelation result.

As mentioned above, since the initial sampling rate is 1.92MHz, the number of sampling points contained in one OFDM symbol is 137, so the time length of one OFDM symbol is 137/1.92MHz, and the phase rotation caused by the frequency offset in the time length of one OFDM symbol yes:

Where θ is the phase value of the autocorrelation result.

Therefore, the estimated value of frequency offset:

It should be pointed out that when the phase rotation caused by the real frequency offset value on one OFDM symbol is less than π, the estimation result in the above formula is the complete frequency offset value. A very large initial frequency offset in a narrowband wireless communication system will cause a phase rotation greater than π, so the estimation result in the above formula is only a fractional part of the frequency offset value, which is called a fractional frequency offset value.

Finally, the frequency offset calibration is performed on the downsampling sequence in the sliding window according to the estimated fractional frequency offset value,

Among them, λ _i is the sampling moment of the i-th sampling point.

M301 differential cross-correlation module

The differential cross-correlation module starts only when the sliding autocorrelation judgment meets the condition of NPSS, and its function is to confirm the existence of NPSS and estimate and calibrate the integer multiple frequency offset, and in the preferred case, it also includes eliminating timing offset.

First, a local sequence without frequency offset is generated according to the protocol, denoted as d _i , the sampling rate of d _i is the same as that of the downsampled received sequence, and di is modulated according to different integer multiple frequency offsets _.

The background technology introduces that the narrowband wireless communication system encounters a maximum frequency deviation of ±25.5KHz during cell search, and there are five possible integer frequency deviations within this range, which are , the above frequency offset values all fall within the maximum frequency offset range.

Using the enumeration method, try each integer multiple frequency offset in the above assumptions to modulate the initial local sequence.

Then, the modulated local sequence is correlated with the sampling sequence output by sliding autocorrelation, and the NPSS sequence within 11 OFDM symbol durations is divided into two sections of approximately equal length for differential correlation, that is, the local sequence with a length of 187 points and the received sampling The sequence is divided into two sections, the length of the first section is 94 points, and the length of the second section is 93 points (or it can also be divided into 93 points for the first section and 94 points for the second section), and the two are correlated.

Where * means to take the conjugate operation.

In the usual technical methods in this field, most of the cross-correlation is obtained by performing a correlation operation on a complete receiving sequence and the local sequence, but in the scheme of the present invention, the complete synchronization sequence is split into approximately equal-length The two segments are obtained by correlating with the local sequence respectively. This is because, according to the protocol, NPSS can be mapped to different antenna ports for transmission in different wireless frames. Therefore, if the sampling method is conventional, it is impossible to directly correlate the NPSS local sequence and the received sequence with a subframe length (187 points). Then combine multiple wireless frame windows to obtain the combined gain; while in this scheme, two segments in a subframe are differentially correlated first, and the antenna port inside a subframe remains unchanged, and the result of differential correlation between different wireless frames remains the same. Can be combined, thus avoiding the problem of switching between antenna ports between wireless frames, thereby obtaining a combined gain.

Normalize the differential correlation results in this 10ms wireless frame, and combine the differential correlation results in multiple 10ms wireless frame windows

in, is the result of normalization within the last 10ms radio frame window.

If the differential cross-correlation result is greater than the threshold value, then find a k value that maximizes the differential cross-correlation result,

It is considered that the differential cross-correlation confirms that the NPSS signal has been detected successfully, and its corresponding frequency offset value is the result of integer times frequency offset estimation.

The total frequency offset estimation result is the sum of the fractional times and integer times frequency offset estimation results .

Perform frequency offset calibration on the received NPSS sequence,

Among them, λ _i is the sampling moment of the i-th sampling point.

In the preferred case in engineering, the differential cross-correlation module also includes the processing of preliminary timing estimates. As previously described, the sampling rate of the initial local sequence d _i is the same as the downsampled received sequence (ie 240kHz). If it is necessary to preliminarily estimate the timing, first generate a local sequence with a high sampling rate, and then try a variety of initial sampling point offsets and perform downsampling. For example, the sampling rate of the generated local sequence is 1.92MHz, as shown in Figure 7. The attempted sampling point offsets are j=0, 1, 2, ... 7 points, the downsampling rate is 8, and the corresponding downsampling sequence is recorded as , the sequence after downsampling is still 240kHz, then perform the differential cross-correlation as mentioned above, and find the maximum differential cross-correlation result,

The corresponding sampling point offset j is the initial timing estimate.

According to the simulation configuration agreed by 3gpp (as shown in Table 1), the detection success rate of more than 95% can be obtained by using the device disclosed in the present invention, and the timing synchronization can be achieved within 4T _samp under the optimal configuration (where T _samp corresponds to 1.92MHz sampling interval), the frequency synchronization error is within 50Hz

Table 1 Performance simulation conditions

Claims (9)

1. A synchronous detection device applied to a narrow-band wireless communication system terminal is characterized by comprising a down-sampling module, a sliding auto-correlation module and a differential cross-correlation module, wherein,

the down-sampling module down-samples the time domain signal of 1.92MHz sampling rate into a signal of 240kHz sampling rate according to a fixed down-sampling pattern by taking an OFDM symbol as a unit length;

the sliding autocorrelation module takes the bit-by-bit movement of sampling point data in a wireless frame processing window length of 10ms as an initial position t, takes the OFDM symbol duration with the length of 11 as a sliding window, divides the sampling points in the sliding window into 11 groups, and performs correlation accumulation at intervals of the sampling points between the two groups;

if the sliding autocorrelation obtained by the calculation of the sliding autocorrelation module is greater than a threshold value, starting the differential cross-correlation module;

the differential cross-correlation module differentiates the synchronous sequence in the sliding window obtained by the sliding self-correlation module into two parts with equal length, and performs cross-correlation accumulation with the locally generated synchronous sequence,

and if the differential cross-correlation result is larger than a threshold value, determining that the detected sequence is a main synchronization sequence.

2. The synchronization detection apparatus according to claim 1,

the down-sampling module divides sampling points of one subframe into 14 OFDM symbol lengths, the sampling patterns in the 1 st and 7 th OFDM symbol time lengths are {10,8,8,8,8,8,8,8,8, 8}, and the sampling patterns in the other OFDM symbol time lengths are {9,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8 }.

3. The synchronization detection apparatus according to claim 1,

the sliding autocorrelation module further comprises a data buffer for buffering the down-sampled data of the last 11 OFDM symbol durations in the last 10ms wireless frame window, and the total processing data of the sliding autocorrelation module is a data sequence of one wireless frame and the last 11 OFDM symbols of the last wireless frame.

4. The synchronization detection apparatus according to claim 1,

before the sliding autocorrelation module performs correlation accumulation between two groups of data intervals of 11 groups of OFDM symbol duration in the sliding window, each group of data sequences needs to be multiplied by scrambling sequences;

the sliding autocorrelation module further needs to perform alpha filtering on a plurality of groups of sliding autocorrelation results of a plurality of 10ms wireless frame processing windows, and perform power normalization on the sliding autocorrelation results of each sliding window.

5. The synchronization detection apparatus according to claim 1,

the sliding autocorrelation module further comprises a sub-module for performing fractional frequency offset estimation and calibration according to the phase value of the sliding autocorrelation result, the fractional frequency offset estimation is calculated according to the following formula,

wherein, arctan { A_tThe result of sliding autocorrelation takes the phase value, 1.92MHz is the sampling rate of the initial time domain data, 137 is the number of samples of one OFDM symbol duration,

and the decimal frequency offset calibration processing is to carry out phase calibration according to the decimal frequency offset estimation value and the sampling time of each sampling point.

6. The synchronization detection apparatus according to claim 1,

and the differential cross-correlation module is used for carrying out power normalization on the differential correlation results and combining the differential correlation results in a plurality of 10ms wireless frame windows.

7. The synchronization detection apparatus according to claim 1,

the differential cross-correlation module further comprises an estimation and calibration sub-module for integer multiple frequency offset,

the integer frequency offset estimation comprises enumerating all possible integer frequency offset values in the maximum frequency offset range to modulate the local sequence, finding out the maximum value of the module value of the result of the differential cross-correlation under each frequency offset value, wherein the frequency offset value corresponding to the maximum module value is the integer frequency offset value,

and the integer frequency offset calibration submodule carries out phase compensation according to the integer frequency offset estimation value and the sampling time of each sampling point.

8. The synchronization detection apparatus according to claim 1,

the differential cross-correlation module further comprises a timing offset estimation sub-module,

the timing offset estimation submodule firstly generates a local sequence with high sampling rate, then enumerates a plurality of timing offsets, down-samples the local sequence to the sampling rate of 240kHz, respectively performs differential cross-correlation with the received data sequence, and takes the timing offset enumerated value corresponding to the maximum module value of the differential cross-correlation value as the estimated timing offset value.

9. A synchronous detection method applied to a narrow-band wireless communication system terminal is characterized by comprising the following processes

Step S101, a down-sampling process, namely down-sampling a time domain signal with a sampling rate of 1.92MHz into a signal with a sampling rate of 240kHz according to a fixed down-sampling pattern by taking an OFDM symbol as a unit length;

step S201, a sliding self-correlation process, namely moving sampling point data in a wireless frame processing window length of 10ms bit by bit to serve as an initial position t, taking an OFDM symbol duration with the length of 11 as a sliding window, dividing sampling points in the sliding window into 11 groups, and performing correlation accumulation at intervals of the sampling points between the two groups;

if the sliding autocorrelation obtained by the calculation of the sliding autocorrelation process is greater than a threshold value, starting a differential cross-correlation process;

step S301, a differential cross-correlation process, which is to differentiate the synchronization sequence in the sliding window obtained in the sliding auto-correlation process into two parts with equal length, and perform cross-correlation accumulation with the locally generated synchronization sequence,

and if the cross-correlation result obtained in the differential cross-correlation process is larger than a threshold value, determining that the detected sequence is a main synchronization sequence.