CN108736931B - Signal synchronization method and device - Google Patents
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- CN108736931B CN108736931B CN201710245743.9A CN201710245743A CN108736931B CN 108736931 B CN108736931 B CN 108736931B CN 201710245743 A CN201710245743 A CN 201710245743A CN 108736931 B CN108736931 B CN 108736931B
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Abstract
A signal synchronization method and apparatus are disclosed. The signal synchronization method comprises the following steps: when the automatic gain control AGC unit locks the received signals, the signals received by each receiving antenna are subjected to delay autocorrelation processing, after the first time length is delayed, the processed received signals of each path are compared with a reference threshold corresponding to the received signals of the path, and whether coarse synchronization is finished or not is determined according to the comparison result of each path; after coarse synchronization is completed, local cross-correlation processing is carried out on each path of received signals, weighted accumulation and filtering are carried out on results of each path of local cross-correlation processing, a maximum value is searched from the filtered signals, and fine synchronization is judged to be completed when the maximum value is searched. The technical scheme can ensure the positioning precision when the received signals are synchronized in a multi-input multi-output system, and reduce the complexity of calculation.
Description
Technical Field
The present invention relates to the field of wireless communication technologies, and in particular, to a signal synchronization method and apparatus.
Background
The performance of the synchronization technique is directly related to the performance of the entire communication system. Without an accurate synchronization algorithm, it can be said that reliable data transmission is not possible, which is a prerequisite for reliable transmission of information. For an Orthogonal Frequency Division Multiplexing (OFDM) system, the requirement of the system for synchronization is very high. Inter-carrier Interference (ICI) and Inter-symbol Interference (ISI) introduced by various synchronization errors may prevent a receiver from correctly receiving data and may destroy orthogonality of subcarriers in the OFDM system.
As shown in fig. 1, in a general OFDM system receiver, an Automatic Gain Control (AGC) section (301) triggers locking of a received signal, and then sends a signal received from each antenna (302) to a Modem (303), and in the Modem, a symbol synchronizer (304) performs positioning synchronization. The symbol synchronizer location synchronization results in a Fast Fourier Transform (FFT) unit (305) providing a reference point to enable a subsequent series of operations (e.g., demodulation). In order not to affect the following demodulation, the symbol synchronization positioning accuracy must be within a certain reasonable range.
Symbol location synchronization is the determination of the start of the OFDM symbol, i.e., the start of each FFT window. As shown in fig. 2, symbol alignment synchronization may occur in four cases: 1) FFT Window 1(Window1) indicates that the timing estimation point is correct, there is no offset, and the demodulated data should be correct; 3) FFT Window 2(Window2) indicates that the timing estimation point falls within the Cyclic Prefix (CP) of the present symbol and leads the optimal timing point; 3) FFT Window 3(Window3) indicates that the timing estimation point falls within the cyclic prefix of the next symbol and lags the optimum timing point; 4) FFT Window 4(Window4) indicates that the timing estimate point falls within the data portion of the previous symbol and precedes the cyclic prefix of the present symbol.
The first of the above four cases is an ideal case, and does not cause symbol positioning errors; in the second case, the introduced positioning deviation can be recovered by the equalizer under the condition that the difference between the introduced positioning deviation and the ideal point is not large, but if the difference is large, the performance of channel smoothing is influenced, so that the performance of the equalizer is reduced; the third and fourth cases introduce ISI and ICI, which significantly degrades the system performance and is therefore to be avoided.
In the case of a multipath channel, it is difficult to locate the ideal point, and therefore a reasonable location range needs to be determined. Firstly, determining allowable positioning deviation according to the number of smooth points of a channel, assuming that the number of the selected smooth points is 11, and ensuring that the phases of the continuous 11 points are continuous during smoothing, namely the maximum phase difference of all frequency points does not exceed pi. The allowable time deviation Δ t is
Under the condition of 20MHz sampling frequency, the time interval between two points in the time domain is 50ns, Δ f is equal to 312.5kHz, therefore, Δ t is equal to 150ns, and the range of the actual positioning point is 3 points leading or lagging the ideal positioning point, thus not influencing the smooth performance.
In addition, in the case of a Multiple-Input Multiple-Output (MIMO) system, each antenna has a fixed delay, and in synchronization, not only Multiple paths but also the fixed delay of the antenna need to be considered.
Therefore, how to provide a synchronization algorithm suitable for a multi-input multi-output system is a problem to be solved, which reduces the complexity of calculation on the premise of not influencing the positioning accuracy.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a signal synchronization method and apparatus, which can ensure the positioning accuracy when receiving signals are synchronized in a mimo system and reduce the complexity of calculation.
The embodiment of the invention provides a signal synchronization method, which comprises the following steps:
when the automatic gain control AGC unit locks the received signals, the signals received by each receiving antenna are subjected to delay autocorrelation processing, after the first time length is delayed, the processed received signals of each path are compared with a reference threshold corresponding to the received signals of the path, and whether coarse synchronization is finished or not is determined according to the comparison result of each path;
after coarse synchronization is completed, local cross-correlation processing is carried out on each path of received signals, weighted accumulation and filtering are carried out on results of each path of local cross-correlation processing, a maximum value is searched from the filtered signals, and fine synchronization is judged to be completed when the maximum value is searched.
An embodiment of the present invention provides a signal synchronization apparatus, including:
the coarse synchronization module is used for carrying out time delay autocorrelation processing on signals received by each path of receiving antenna when the automatic gain control AGC unit locks the receiving signals, comparing the processed receiving signals of each path with a reference threshold corresponding to the received signals of the path after delaying for a first time length, and determining whether coarse synchronization is finished or not according to comparison results of each path;
and the fine synchronization module is used for performing local cross-correlation processing on each path of received signals after coarse synchronization is completed, performing weighted accumulation and filtering on results of each path of local cross-correlation processing, searching a maximum value from the filtered signals, and judging that fine synchronization is completed when the maximum value is searched.
Compared with the prior art, the embodiment of the invention provides a signal synchronization method and a device, when an automatic gain control AGC unit locks a received signal, the signal received by each receiving antenna is subjected to time delay autocorrelation processing, after the time is delayed for a first time length, the processed received signal of each path is compared with a reference threshold corresponding to the received signal of the path, and whether coarse synchronization is finished or not is determined according to the comparison result of each path; after coarse synchronization is completed, local cross-correlation processing is carried out on each path of received signals, weighted accumulation and filtering are carried out on results of each path of local cross-correlation processing, a maximum value is searched from the filtered signals, and fine synchronization is judged to be completed when the maximum value is searched. The embodiment of the invention can ensure the positioning precision when the received signals are synchronized in a multi-input multi-output system and reduce the complexity of calculation.
Drawings
FIG. 1 is a diagram of a prior art digital receiver receiving and demodulating a signal;
FIG. 2 is a diagram illustrating a positioning point for symbol positioning synchronization in the prior art;
fig. 3 is a flowchart of a signal synchronization method according to embodiment 1 of the present invention;
fig. 4 is a block diagram illustrating a coarse synchronization process in embodiment 1 of the present invention;
fig. 5 is a timing diagram of delay triggered coarse synchronization detection in embodiment 1 of the present invention;
fig. 6 is a schematic block diagram of fine synchronization processing in embodiment 1 of the present invention;
fig. 7 is a schematic diagram of coarse synchronization detection triggered by AGC lock time delay in example 1 of the present invention;
fig. 8 is a schematic diagram of reference threshold generation and coarse synchronization detection triggering in example 2 of the present invention;
fig. 9 is a schematic diagram of a signal synchronization apparatus according to embodiment 2 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the embodiments and features of the embodiments in the present application may be arbitrarily combined with each other without conflict.
Example 1
As shown in fig. 3, an embodiment of the present invention provides a signal synchronization method, including:
step S310, when the automatic gain control AGC unit locks the received signal, the signal received by each receiving antenna is delayed and self-correlated, after the first time length is delayed, the processed received signal of each path is compared with the reference threshold corresponding to the received signal of the path, and whether coarse synchronization is finished or not is determined according to the comparison result of each path;
step S320, after the coarse synchronization is completed, performing local cross-correlation processing on each path of received signals, performing weighted accumulation and filtering on the results of the local cross-correlation processing, searching for a maximum value from the filtered signals, and determining that fine synchronization is completed when the maximum value is searched.
In an embodiment, the performing delayed autocorrelation processing on a signal received by any receiving antenna includes:
carrying out symbol autocorrelation operation of delaying N beats on a received signal r (N) according to the period N of the short training sequence to obtain a first signal Lambda (m);
the symbol autocorrelation operation of the delayed N beats can be represented by the following formula (2-1):
wherein N isA period of a Short Training Field (STF), if a sampling frequency is 20MHz, N is equal to 16; r (n) is a received signal, r*(n) is the conjugate of the received signal; sign () is a sign taking function;
the short training sequence is used for signal detection, AGC power adjustment, coarse synchronization, etc., and the STF belongs to a sequence known by the transmitting side and the receiving side, and by the sequence, it can determine what signal is received, and can provide a certain reference and buffer for the subsequent fine synchronization processing.
In one embodiment, the first length of time is the duration of the short training sequence T1 minus the maximum time T2 for the AGC unit to lock onto the received signalmaxThe length of time thereafter;
wherein, the time T2 for locking the received signal by the AGC unit does not exceed T2max；
In one embodiment, the reference threshold corresponding to each received signal is obtained by averaging the delayed autocorrelation results of the received signal in a short training sequence period and then multiplying by 0.5.
In one embodiment, comparing each processed received signal with a reference threshold corresponding to the received signal, and determining whether coarse synchronization is completed according to each comparison result, includes:
if a path of processed received signals reaches a reference threshold corresponding to the path of received signals and reaches the reference threshold for a period of time, judging that the path of received signals meets the requirement of coarse synchronization;
and judging to finish coarse synchronization when at least one path of received signals meets the coarse synchronization requirement.
Wherein the duration is a preset value, such as 5 sampling points;
in an embodiment, the performing local cross-correlation processing on any path of received signals includes:
performing local cross-correlation operation on the received signal r (m) according to the period N of the long training sequence to obtain a second signal (m);
wherein the local cross-correlation operation can be represented by the following formula (2-2):
wherein, c (n) is the tap coefficient of the filter, and the tap coefficient of the filter is designed according to the value of the long training sequence; r is*() Is the conjugate of the received signal;
in one embodiment, the weighted accumulation and filtering of the results of the local cross-correlation processes comprises:
performing equal weight accumulation on the results of the local cross-correlation processing of each path to obtain a third signal;
sending the third signal into a filter with the number of taps a for filtering;
the product of the tap number a of the filter and the sampling interval of the received signal is greater than or equal to the maximum delay among the transmitting antennas; the value of the tap coefficient corresponding to the signal sent by the first sending antenna in the a tap coefficients is larger than the values of other tap coefficients; any other transmit antenna than the first transmit antenna precedes the first transmit antenna in transmitting signals.
The maximum value is searched from the filtered signal, the position where the maximum value appears is the end position of the LTF, and is also the start of the next symbol, and because each symbol is preceded by a guard interval, the start position of each symbol can be determined according to the end position of the LTF and the length of the guard interval, and therefore, when the maximum value is searched, it is determined that fine synchronization is completed.
In one embodiment, as shown in fig. 4, the coarse synchronization process may include the following steps:
1) after the AGC unit locks the received signal, generating a first trigger signal by a trigger signal generator (401);
2) processing signals received by each receiving antenna (402) according to the first trigger signal;
3) processing a received signal by two paths, wherein one path of signal is sent to a symbol taking unit to perform symbol taking operation, the taken symbol is stored in a First Input First Output (FIFO) buffer (404) with the depth of N (N is the period of STF, for example, N is 16), and the other path of signal is sent to a conjugate taking unit (405) to perform conjugate taking operation; multiplying the output signal of the first FIFO buffer and the output signal of the conjugate unit;
4) dividing the multiplied signals into two paths, wherein one path of signals is stored in a second First-in First-out (FIFO) buffer (406) with the depth of N (N is the period of STF, for example, N is 16), and the other path of data is subtracted from the Output signal of the second FIFO buffer, and the subtracted signals are sent to an accumulation modulus-taking unit (407) for accumulation modulus-taking operation, so that a delay autocorrelation operation with the window length of N (N is 16) is completed;
5) starting from locking a received signal by an AGC unit, a trigger signal generator (401) outputs a second trigger signal to a mean value operation unit (408) after delaying a first time threshold T1, the mean value operation unit extracts a delay autocorrelation result with a certain window length, averages the delay autocorrelation result to obtain a reference threshold, and simultaneously triggers coarse synchronization detection;
6) a comparison unit (409) corresponding to each receiving antenna compares the autocorrelation result output by the accumulation modulus taking unit with the reference threshold output by the mean value operation unit to obtain a 1-bit comparison result;
7) sending the 1-bit comparison result output by the comparison unit (409) corresponding to each path of receiving antenna into an OR logic operation unit (410) to generate a 1-bit coarse synchronization result; for example, when the coarse synchronization result is 1, it is determined that the coarse synchronization is completed;
as shown in fig. 5, for example, an AGC lock signal is used to perform delay triggering, a delay autocorrelation result of a certain window length is extracted and averaged to obtain a threshold, coarse synchronization detection is triggered, the delay autocorrelation result is sequentially compared with the threshold, coarse synchronization is not triggered when a point is lower than the threshold, and coarse synchronization is triggered only when the delay autocorrelation result is continuously lower than the threshold for 5 times. Because the coarse synchronization detection is started not from the moment of AGC locking but from the moment of obtaining the reference threshold, the coarse synchronization detection of the time when the AGC is locked to the threshold and generates the threshold is reduced, and the occurrence of error synchronization can be effectively reduced.
The purpose of the coarse synchronization is to trigger the fine synchronization calculation and provide a proper calculation window length for the fine synchronization.
In the fine synchronization process, a digital filter with a tap number of 64 is designed by using the value of a Long Training Field (LTF) in one period, and a received signal passes through the filter and actually performs a cross-correlation operation with the tap coefficient of the filter, where the cross-correlation operation can be expressed by the following formula (2-2):
where N represents the length of the cross-correlation calculation, N equals 64; r (m) is a received signal, and c (n) is a tap coefficient of the filter;
the long training sequence LTF has a period 4 times that of the STF, is the same as that of one OFDM, and can be used for fine synchronization, fine frequency offset estimation and signal estimation. Embodiments of the present invention take advantage of its strong correlation properties, and store a segment of the processed LTF (i.e., the tap coefficients of the filter) locally, and consider the received signal as being synchronized when it correlates (peaks) with the local LTF.
In the process of fine synchronization, for the MIMO system, except for the first antenna, the other antennas perform advance processing (maximum advance is 200ns, and sampling frequency for 20MHz is 4 points) through time domain cyclic shift, which results in that the MIMO system cannot simply detect the cross-correlation peak directly as a single-input single-Output (SISO) system. For MIMO, the result of the synchronization must be the position where the first peak occurs. In order to accurately locate an ideal position, the embodiment of the invention searches the maximum value of the output result of the filter in a certain range by passing the cross-correlation calculation result through a filter with the tap number of 6, namely the final fine synchronization result.
In addition, as can be seen from fig. 1, a third situation may occur in the synchronization position, that is, the timing estimation point falls within the cyclic prefix of the next symbol and lags behind the optimal timing point, so the dynamic range of positioning synchronization can be improved by the positioning offset processing. For example, moving the synchronization position forward by 6 points starts to extract each OFDM symbol, and before performing FFT, the values of the first six points of the symbol are moved to the last position of the symbol, which allows the anchor point to swing left and right at the optimal anchor point. Therefore, the positioning synchronization point can be ensured to move left and right at the optimal positioning point, intersymbol interference is avoided, and the dynamic range of the positioning synchronization is improved.
In one embodiment, based on the above considerations, as shown in fig. 6, the fine synchronization process may include the following steps:
1) a coarse synchronization completion trigger generator (601) for generating a third trigger (corresponding to a time delay of T2 after the AGC locking time);
2) sending the signals received by each receiving antenna into each corresponding first filter (602) for filtering according to the third trigger signal, and then sending the signals into each corresponding module taking unit (603) for module taking;
the tap coefficient of the filter is correspondingly processed according to the time domain signal of the long training sequence, firstly, the sign of the tap coefficient of the filter is determined after the sign of the time domain signal of the long training sequence is taken, and then the filter coefficient is set to be 0, 1 and 2 according to the amplitude of the time domain signal of the long training sequence, because the amplitude is large, the anti-noise capability is strong, and the confidence coefficient is high, a larger weight is given. The tap coefficient c (n) of such a filter is a complex number (e.g., 1+2i) composed of 0, 1, 2;
3) signals after modulus extraction of each antenna are sent to an accumulator (604) for summation operation, which is equivalent to equal weight superposition of cross-correlation operation results of each antenna;
4) inputting the signal output by the accumulator to a second filter (605) for processing, wherein the processing is used for reducing the influence of different delays and multipath of multiple antennas;
the second filter is equivalent to a sliding window summation, one value is weighted, the sliding window can reduce the influence of different delays and multipath of the antenna, the weighting can improve the peak intensity of the first transmitting antenna, the peak of the first transmitting antenna is favorably positioned, and the accuracy of the positioning result is improved.
5) Inputting the output signal of the second filter into a maximum value searching unit (606) for maximum value searching to obtain a fine synchronization result;
6) inputting the result output by the maximum value searching unit into a positioning offset unit (607), moving the synchronous position forward by 6 points to start extracting each OFDM symbol, moving the numerical values of the first six points of the symbol to the final position of the symbol before FFT, and obtaining the initial position of the extracted FFT window after positioning offset; in addition, the point of the positioning offset is moved to the end of the symbol by utilizing the periodic characteristic of the symbol after the data is extracted;
the processing in the coarse synchronization process and the fine synchronization process is further described below by some examples.
Example 1
After AGC lock, the received signal enters the modem, as shown in fig. 7. In this case, the coarse synchronization detection is not performed immediately, but is performed after a certain time delay. The time of delay (T) is obtained by subtracting the time of AGC latest lock (701) from the time of the end of the short training sequence (702) used for coarse synchronization.
In actual operation, after AGC lock (703), a delay time (T) is passed to obtain a threshold (704), which causes coarse synchronization detection (705) to occur after the threshold is generated. This prevents coarse synchronization detection before the coarse synchronization detection 705 is triggered after the AGC lock 703, which effectively reduces the occurrence of false synchronization.
Example 2
As shown in fig. 8, the received signal is processed by the delayed autocorrelation to obtain an output result (801), the AGC lock delay starts to calculate a threshold (802) by using the output result (801), the calculation of the threshold is performed by extracting 16 values of the output result (801) from the start of the trigger and then averaging, after the threshold calculation is completed, the threshold becomes effective, the coarse synchronization detection starts to be performed, then the output result (801) and the threshold are compared by a comparator (803) and output a comparison result of 1 bit, the comparison result passes through a 5-tap filter (804) with all tap coefficients of 1, the output data of the filter is compared with the value (805) in the register, wherein the value in the register is set to 5, and equality proves that the coarse synchronization of the antenna is detected; the 5-tap filter (804) functions to: the coarse synchronization trigger is considered to be when 5 continuous points reach a threshold value;
the results of the coarse synchronization detection for all antennas are processed by logical operation or (806), i.e. as long as one antenna coarse synchronization is detected, the coarse synchronization process is completed.
The coarse synchronization completion will trigger the fine synchronization calculation and detection.
Example 3
As shown in fig. 6, tap coefficients of the first filter (602) are designed according to the time domain value of the long training sequence, the real part and the imaginary part of the time domain value of the long training sequence are respectively averaged, the average value is divided by 2 to obtain a threshold value, the real part and the imaginary part of the time domain value of the long training sequence are respectively divided by the corresponding threshold values, and then the calculation result is rounded (the absolute value exceeds 2 to obtain 2) to obtain a tap coefficient c' (n) of the final filter.
In the above equation (3-1), c (N) is to compress the time domain signal of the original LTF, i.e. to use very small bits to represent the characteristics of the time domain signal of the LTF, x (N) is the time domain signal of the LTF, N ═ 64 represents the period of the LTF, and round () is an integer function;
in the above equation (3-2), c' (n) is a tap coefficient (i.e., a locally stored long training sequence);
for the second filter (605), the second filter has a total of 6 taps with tap coefficients: {1,1,1,1,2,1}, the second filter can resist multipath effect and delay among different antennas, and the weight value of the peak value of the first receiving antenna is increased to position the synchronization result on the first receiving antenna.
As shown in fig. 9, an embodiment of the present invention provides a signal synchronization apparatus, including:
a coarse synchronization module 901, configured to perform a delay autocorrelation process on signals received by each receiving antenna when the AGC unit locks a received signal, compare the processed received signals with a reference threshold corresponding to the received signal after delaying for a first time period, and determine whether coarse synchronization is completed according to a comparison result of each path;
and a fine synchronization module 902, configured to perform local cross-correlation processing on each received signal after coarse synchronization is completed, perform weighted accumulation and filtering on results of the local cross-correlation processing, search for a maximum value from the filtered signals, and determine that fine synchronization is completed when the maximum value is searched.
In an embodiment, the coarse synchronization module is configured to perform a delay autocorrelation process on a signal received by any one of the receiving antennas in the following manner:
carrying out symbol autocorrelation operation of delaying N beats on a received signal r (N) according to the period N of the short training sequence to obtain a first signal Lambda (m);
the symbol autocorrelation operation of the delayed N beats can be represented by the following formula:
where N is the period of the short training sequence STF, r (N) is the received signal, r*(n) is the conjugate of the received signal; sign () is a sign taking function.
In one embodiment, the first length of time is the duration of the short training sequence T1 minus the AGC elementMaximum time T2 for locking received signalmaxThe latter time length.
In one embodiment, the reference threshold corresponding to each received signal is obtained by averaging the delayed autocorrelation results of the received signal in a short training sequence period and then multiplying by 0.5.
In one embodiment, the coarse synchronization module is configured to compare each processed received signal with a reference threshold corresponding to the received signal, and determine whether coarse synchronization is completed according to a comparison result of each path:
if a path of processed received signals reaches a reference threshold corresponding to the path of received signals and reaches the reference threshold for a period of time, judging that the path of received signals meets the requirement of coarse synchronization;
and judging to finish coarse synchronization when at least one path of received signals meets the coarse synchronization requirement.
In an embodiment, the fine synchronization module is configured to perform local cross-correlation processing on any one path of received signals by using the following method:
performing local cross-correlation operation on the received signal r (m) according to the period N of the long training sequence to obtain a second signal (m);
wherein the local cross-correlation operation may be represented by the following formula:
wherein, c (n) is the tap coefficient of the filter, and the tap coefficient of the filter is designed according to the value of the long training sequence; r is*() Is the conjugate of the received signal.
In one embodiment, the fine synchronization module is configured to perform weighted accumulation and filtering on the results of the local cross-correlation processes in the following manners:
performing equal weight accumulation on the results of the local cross-correlation processing of each path to obtain a third signal;
sending the third signal into a filter with the number of taps a for filtering;
the product of the tap number a of the filter and the sampling interval of the received signal is greater than or equal to the maximum delay among the transmitting antennas; the value of the tap coefficient corresponding to the signal sent by the first sending antenna in the a tap coefficients is larger than the values of other tap coefficients; any other transmit antenna than the first transmit antenna precedes the first transmit antenna in transmitting signals.
It should be noted that the present invention can be embodied in other specific forms, and various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention.
Claims (14)
1. A method of signal synchronization, comprising:
when the automatic gain control AGC unit locks the received signals, the signals received by each receiving antenna are subjected to delay autocorrelation processing, after the first time length is delayed, the processed received signals of each path are compared with a reference threshold corresponding to the received signals of the path, and whether coarse synchronization is finished or not is determined according to the comparison result of each path;
after coarse synchronization is completed, local cross-correlation processing is carried out on each path of received signals, weighted accumulation and filtering are carried out on results of each path of local cross-correlation processing, a maximum value is searched from the filtered signals, and fine synchronization is judged to be completed when the maximum value is searched.
2. The method of claim 1, wherein:
the method for carrying out time delay autocorrelation processing on signals received by any path of receiving antenna comprises the following steps:
carrying out symbol autocorrelation operation of delaying N beats on a received signal r (N) according to the period N of the short training sequence to obtain a first signal Lambda (m);
the symbol autocorrelation operation of the delayed N beats can be represented by the following formula:
where N is the period of the short training sequence STF, r (N) is the received signal, r*(n) is the conjugate of the received signal; sign () is a sign taking function.
3. The method of claim 1 or 2, wherein:
the first time length is the duration T1 of the short training sequence minus the maximum time T2 for the AGC unit to lock onto the received signalmaxThe latter time length.
4. The method of claim 2, wherein:
the reference threshold corresponding to each path of received signal is obtained by taking an average value according to the time delay autocorrelation result of the path of received signal in a short training sequence period and then multiplying the average value by 0.5.
5. The method of claim 1, wherein:
comparing the processed received signals with the reference threshold corresponding to the received signals, and determining whether coarse synchronization is completed according to the comparison result of each path, including:
if a path of processed received signals reaches a reference threshold corresponding to the path of received signals and reaches the reference threshold for a period of time, judging that the path of received signals meets the requirement of coarse synchronization;
and judging to finish coarse synchronization when at least one path of received signals meets the coarse synchronization requirement.
6. The method of claim 1, wherein:
carrying out local cross-correlation processing on any path of received signals, comprising the following steps:
performing local cross-correlation operation on the received signal r (m) according to the period N of the long training sequence to obtain a second signal (m);
wherein the local cross-correlation operation may be represented by the following formula:
wherein, c (n) is the tap coefficient of the filter, and the tap coefficient of the filter is designed according to the value of the long training sequence; r is*() Is the conjugate of the received signal.
7. The method of claim 1, wherein:
performing weighted accumulation and filtering on the results of the local cross-correlation processing of each path, comprising the following steps:
performing equal weight accumulation on the results of the local cross-correlation processing of each path to obtain a third signal;
sending the third signal into a filter with the number of taps a for filtering;
the product of the tap number a of the filter and the sampling interval of the received signal is greater than or equal to the maximum delay among the transmitting antennas; the value of the tap coefficient corresponding to the signal sent by the first sending antenna in the a tap coefficients is larger than the values of other tap coefficients; any other transmission antenna than the first transmission antenna transmits a signal before the first transmission antenna transmits a signal.
8. A signal synchronization apparatus, comprising:
the coarse synchronization module is used for carrying out time delay autocorrelation processing on signals received by each path of receiving antenna when the automatic gain control AGC unit locks the receiving signals, comparing the processed receiving signals of each path with a reference threshold corresponding to the received signals of the path after delaying for a first time length, and determining whether coarse synchronization is finished or not according to comparison results of each path;
and the fine synchronization module is used for performing local cross-correlation processing on each path of received signals after coarse synchronization is completed, performing weighted accumulation and filtering on results of each path of local cross-correlation processing, searching a maximum value from the filtered signals, and judging that fine synchronization is completed when the maximum value is searched.
9. The apparatus of claim 8, wherein:
the coarse synchronization module is used for performing time-delay autocorrelation processing on signals received by any path of receiving antenna by adopting the following modes:
carrying out symbol autocorrelation operation of delaying N beats on a received signal r (N) according to the period N of the short training sequence to obtain a first signal Lambda (m);
the symbol autocorrelation operation of the delayed N beats can be represented by the following formula:
where N is the period of the short training sequence STF, r (N) is the received signal, r*(n) is the conjugate of the received signal; sign () is a sign taking function.
10. The apparatus of claim 8 or 9, wherein:
the first time length is the duration T1 of the short training sequence minus the maximum time T2 for the AGC unit to lock onto the received signalmaxThe latter time length.
11. The apparatus of claim 9, wherein:
the reference threshold corresponding to each path of received signal is obtained by taking an average value according to the time delay autocorrelation result of the path of received signal in a short training sequence period and then multiplying the average value by 0.5.
12. The apparatus of claim 8, wherein:
the coarse synchronization module is used for comparing the processed receiving signals of each path with a reference threshold corresponding to the receiving signals of the path in the following mode, and determining whether coarse synchronization is finished according to the comparison result of each path:
if a path of processed received signals reaches a reference threshold corresponding to the path of received signals and reaches the reference threshold for a period of time, judging that the path of received signals meets the requirement of coarse synchronization;
and judging to finish coarse synchronization when at least one path of received signals meets the coarse synchronization requirement.
13. The apparatus of claim 8, wherein:
the fine synchronization module is used for performing local cross-correlation processing on any path of received signals in the following modes:
performing local cross-correlation operation on the received signal r (m) according to the period N of the long training sequence to obtain a second signal (m);
wherein the local cross-correlation operation may be represented by the following formula:
wherein, c (n) is the tap coefficient of the filter, and the tap coefficient of the filter is designed according to the value of the long training sequence; r is*() Is the conjugate of the received signal.
14. The apparatus of claim 8, wherein:
and the fine synchronization module is used for performing weighted accumulation and filtering on the results of the local cross-correlation processing of each path by adopting the following modes:
performing equal weight accumulation on the results of the local cross-correlation processing of each path to obtain a third signal;
sending the third signal into a filter with the number of taps a for filtering;
the product of the tap number a of the filter and the sampling interval of the received signal is greater than or equal to the maximum delay among the transmitting antennas; the value of the tap coefficient corresponding to the signal sent by the first sending antenna in the a tap coefficients is larger than the values of other tap coefficients; any other transmission antenna than the first transmission antenna transmits a signal before the first transmission antenna transmits a signal.
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| CN1534908A (en) * | 2003-03-28 | 2004-10-06 | 中国科学技术大学 | Frame timing synchronization method of orthogonal frequency division multiplex signal |
| CN101064700A (en) * | 2006-04-26 | 2007-10-31 | 电子科技大学 | Method for synchronization of multi-input multi-output OFDM system |
| WO2007138453A2 (en) * | 2006-05-31 | 2007-12-06 | Nokia Corporation | Method product providing synchronization for ofdma downlink signal |
| CN101534280A (en) * | 2009-04-15 | 2009-09-16 | 大唐微电子技术有限公司 | Timing synchronous receiving method and device thereof |
| CN103200144A (en) * | 2013-03-28 | 2013-07-10 | 灵芯微电子科技（苏州）有限公司 | Synchronizing method used for MIMO-OFDM system |
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| CN1534908A (en) * | 2003-03-28 | 2004-10-06 | 中国科学技术大学 | Frame timing synchronization method of orthogonal frequency division multiplex signal |
| CN101064700A (en) * | 2006-04-26 | 2007-10-31 | 电子科技大学 | Method for synchronization of multi-input multi-output OFDM system |
| WO2007138453A2 (en) * | 2006-05-31 | 2007-12-06 | Nokia Corporation | Method product providing synchronization for ofdma downlink signal |
| CN101534280A (en) * | 2009-04-15 | 2009-09-16 | 大唐微电子技术有限公司 | Timing synchronous receiving method and device thereof |
| CN103200144A (en) * | 2013-03-28 | 2013-07-10 | 灵芯微电子科技（苏州）有限公司 | Synchronizing method used for MIMO-OFDM system |
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