CN101442360A - Time synchronization method and apparatus - Google Patents

Abstract

The embodiment of the invention relates to a time synchronization method and a time synchronization device. The time synchronization method comprises the following steps: a first metric function which characterizes the autocorrelation degree of a received signal is received according to an autocorrelation function of the received signal; the first metric function is subject to accumulated operation to obtain a second metric function; the frame detection and the timing synchronization are performed according to the second metric function; and the time synchronization device comprises a processing module used for obtaining the first metric function, an accumulation module used for performing accumulated operation on the first metric function to obtain the second metric function, and a frame detection and timing synchronization module used for performing the frame detection and the timing synchronization according to the second metric function. The time synchronization method and the time synchronization device can improve the accuracy of the frame detection and the timing synchronization, and reduce the false-alarm probability of the frame detection.

Description

Method for synchronizing time and device

Technical field

The embodiment of the invention relates to moving communicating field, especially a kind of method for synchronizing time and device.

Background technology

Wireless access the Internet and radio multimedium data service have promoted the fast development of wireless communication technology, and the communication technology is broadband, mobile becomes development in future trend.Wherein, micro-wave access global inter communication (Worldwide Interoperability for Microwave Access is hereinafter to be referred as WiMAX) technology becomes metropolitan area broadband wireless access mainstream technology gradually.WIMAX is a kind of wireless access wide band technology, comprises the air interface technologies between base station and the subscriber station, and the frame structure of physical layer, system design parameters etc. have been made detailed regulation.The WiMAX system supports multiple physical-layer air interfaces, and wherein the support to OFDM (Othogonal Frequency Division Multiplex is hereinafter to be referred as OFDM) modulation technique air interface is the basic demand of WIMAX system.The OFDM technology is a kind of orthogonal multiple carrier technology, is a bandwidth carrier is divided into a plurality of subcarriers, and these subcarriers are mutually orthogonal, and frequency spectrum is overlapped, and transmits data simultaneously on several subcarriers.Less than the coherence bandwidth of signal, on frequency-selective channel, the decline on each subcarrier is a flat fading to the width of subcarrier, has reduced intersymbol interference so mostly, and has reduced the complexity of channel equalization, is fit to the transmission of high-speed data.

There is strict requirement in WiMAX system based on the OFDM technology for the orthogonality between the subcarrier, and what the orthogonality between the subcarrier directly influenced system is energy, and orthogonality is by finishing synchronously.The base station receiving terminal of WiMAX system generally is regularly synchronous earlier (frame, symbol, sample value is synchronous), back frequency deviation is synchronous, in the practical application, adopt Cyclic Prefix (Circle Prefix, hereinafter to be referred as CP) ofdm system, regularly require looser relatively synchronously to frame, as long as the initial moment of frame drops within the CP length, just can not destroy the orthogonality of subcarrier, just need carry out phase compensation, and responsive to deviation ratio, frequency deviation not only can influence the deflection of phase place, also can destroy the orthogonality between each subcarrier, therefore the WiMAX system requirements is at fast fourier transform (Fast Fourier Transform, hereinafter to be referred as FFT) carry out before the conversion synchronously slightly, FFT after, carry out synchronously carefully, frame detects and thick regularly synchronous directly influence frequency offset estimating performance and follow-up cell identification performance.Under multi-path environment, in order to obtain best systematic function, need to obtain best frame regularly synchronously, satisfying the time delay expansion requirement of system, and the regularly synchronous precision of the frame of prior art is accurate inadequately.

Summary of the invention

The embodiment of the invention provides a kind of method for synchronizing time and device, detects and regularly synchronous accuracy with achieve frame.

The embodiment of the invention provides a kind of method for synchronizing time, comprising:

Carry out auto-correlation processing and calculating energy to received signal and handle, obtain first metric function, described first metric function characterizes the auto-correlation degree of described received signal;

Described first metric function added up obtain second metric function;

Carrying out frame according to described second metric function detects with regularly synchronously.

The embodiment of the invention provides a kind of time synchronism apparatus, comprising:

Processing module is used for carrying out to received signal obtaining first metric function in auto-correlation processing and the calculating energy place, and described first metric function characterizes the auto-correlation degree of described received signal;

Accumulator module, being used for described first metric function added up obtains second metric function;

Frame detects and the timing synchronization module, is used for carrying out frame according to described second metric function and detects with regularly synchronously.

The embodiment of the invention is by obtaining second metric function to adding up of first metric function, can improve the plateau phenomenon and the burr phenomena of first metric function, make second metric function only have a peak value, and become smooth, and then detect with timing synchronous according to the frame that second metric function is carried out, can improve the accuracy that frame detects and timing is synchronous, and on the alarm dismissal probability basis of invariable, reduce the false alarm probability that frame detects.

Description of drawings

Fig. 1 is embodiment of the invention method for synchronizing time embodiment one flow chart;

Fig. 2 is embodiment of the invention method for synchronizing time embodiment two flow charts;

Fig. 3 is the pairing schematic diagram of embodiment of the invention method for synchronizing time Fig. 2;

Fig. 4 is the schematic diagram of the lead code time domain specification in the embodiment of the invention method for synchronizing time;

Fig. 5 a is that first metric function in the embodiment of the invention method for synchronizing time carries out that frame detects and the schematic diagram of the plateau phenomenon that regularly occurs synchronously the time;

Fig. 5 b is that first metric function in the embodiment of the invention method for synchronizing time carries out that frame detects and the schematic diagram of the burr phenomena that regularly occurs synchronously the time;

Fig. 6 a is the schematic diagram of first metric function under the high s/n ratio situation in the embodiment of the invention method for synchronizing time;

Fig. 6 b is the schematic diagram of second metric function under the high s/n ratio situation in the embodiment of the invention method for synchronizing time;

Fig. 7 a is the schematic diagram of first metric function under the low signal-to-noise ratio situation in the embodiment of the invention method for synchronizing time;

Fig. 7 b is the schematic diagram of second metric function under the low signal-to-noise ratio situation in the embodiment of the invention method for synchronizing time;

Fig. 8 carries out the comparison diagram of frame false alarm rate when detecting for utilize first metric function and second metric function in the embodiment of the invention method for synchronizing time;

Fig. 9 is embodiment of the invention time synchronism apparatus embodiment one structural representation;

Figure 10 is embodiment of the invention time synchronism apparatus embodiment two structural representations;

Figure 11 is the structural representation of processing module one embodiment in the embodiment of the invention time synchronism apparatus.

Embodiment

Further specify the technical scheme of the embodiment of the invention below in conjunction with the drawings and specific embodiments.

Fig. 1 is the flow chart of the method for synchronizing time of the embodiment of the invention one, and this embodiment specifically comprises:

Step 11: carry out auto-correlation processing and calculating energy to received signal and handle, obtain first metric function, this first metric function characterizes the auto-correlation degree of this received signal.

Step 12: above-mentioned first metric function added up obtains second metric function;

Step 13: carry out frame according to above-mentioned second metric function and detect with regularly synchronously.

Fig. 2 is the flow chart of the method for synchronizing time of the embodiment of the invention two, referring to the schematic diagram of the embodiment of the invention shown in Figure 3 two method for synchronizing time, and r among Fig. 3 _dExpression received signal d sampling constantly, in like manner r _D+LBe that received signal d+L samples constantly, as shown in Figure 2, this embodiment specifically comprises:

Step 21: the base station receiving terminal receives the digital signal after analog to digital conversion;

For example lead code (preamble) sequence used of different districts (Cell), different sector (Segment) has three types lead code carrier set, and the carrier set of supposing lead code is by following formula definition:

PreambleCarrierSet _n＝n+3k

Wherein: PreambleCarrierSet _nFor distributing to all subcarrier set of a specific preamble;

N is a lead code carrier set index, and value is: n=0,1,2;

K is an index, is 2048 system for FFT, and value is: k=0, and 1 ..., 567;

Above-mentioned lead code carrier set formula has determined this lead code to have three sections repeat property on time domain, and this lead code time domain specification can be referring to Fig. 4, and wherein, Preamble is the useful symbol of lead code, and S1, S2, S3 are the useful symbols of three sections repetitions of lead code.

Certainly, the lead code carrier set is not limited to shown in the above-mentioned formula, and when for example lead code had four sections repeat property on time domain, the parameter before the index k in the above-mentioned formula was 4, and the value of lead code carrier set index n is 0,1,2,3; Be that the preceding parameter of index k is the segments with lead code of segmentation repeat property, the span of lead code carrier set index n is [0, segments-1].And above-mentioned lead code can be that the single antenna of the ofdm system of single antenna sends, and also can be wherein antenna transmission of many antennas ofdm system.

Step 22: first received signal that receives according to receiving terminal obtains the energy of first received signal; First received signal is carried out delay process, and obtain the energy of second received signal according to second received signal that receives after the time-delay; This first received signal and second received signal are carried out relevant treatment, obtain the auto-correlation function of received signal;

Wherein, the starting point of first received signal is that received signal is at d sampling r constantly _d, the starting point of second received signal is that received signal is at d+L sampling r constantly _D+L, L is the block sampling number of lead code, is example with above-mentioned lead code with three sections repeat property, L is 1/3 of the useful symbol Preamble of a lead code length, the length of each segmentation S1 or S2 or S3 in the promptly above-mentioned lead code.

Then: through hits is that the segments of the block sampling number of lead code subtracts one times, is 3 with above-mentioned segments, and the block sampling number is that the lead code of L is an example, is 2L, the processing of calculating energy after, the energy R of first received signal ₁(d) be:

$R_1\left(d\right)=\underset{m=0}{\overset{2L-1}{\mathrm{\Σ}}}{\left|r_{d+m}\right|}^2$

The energy R of second received signal ₂(d) be:

$R_2\left(d\right)=\underset{m=0}{\overset{2L-1}{\mathrm{\Σ}}}{\left|r_{d+m+L}\right|}^2$

First received signal and second received signal are carried out the relevant treatment hits is, the segments of the block sampling number of lead code subtracts one times, is example with above-mentioned lead code, is 2L, relevant treatment after the auto-correlation function P (d) of received signal be:

$P\left(d\right)=\underset{m=0}{\overset{2L-1}{\mathrm{\Σ}}}\left(r_{d+m}^{*}{r}_{d+m+L}\right)$

Above-mentioned auto-correlation function and energy function can also obtain by the method for recursion, to reduce operand, that is:

$P\left(d\right)=P(d-1)+r_{d+2L-1}^{*}{r}_{d+3L-1}-r_{d-1}^{*}{r}_{d-1+L}$

R ₁(d)＝R ₁(d-1)+|r _d+2L-1| ²-|r _d-1| ²

R ₂(d)＝R ₂(d-1)+|r _d+3L-1| ²-|r _d-1+L| ²

Step 23: above-mentioned auto-correlation function is asked mould square, and carry out normalization with the energy of the energy of first received signal and second received signal and obtain first metric function;

The i.e. first metric function M (d) obtains by following formula:

$M\left(d\right)=\frac{{\left|P\left(d\right)\right|}^2}{R_1\left(d\right)R_2\left(d\right)}$

Also can be used for frame detection and regularly synchronous by first metric function, promptly set up a frame detection threshold λ, when the value of first metric function surpassed this thresholding, then expression received a frame, cross peak time corresponding position behind the thresholding with first metric function, as the timing sync bit.

But, because the existence of Cyclic Prefix, (Cyclic Prefix is duplicating of lead code useful symbol end), plateau phenomenon can appear in first metric function, therefore influences timing accuracy; And when low signal-to-noise ratio, serious burr phenomena can appear in first metric function, also can influence timing accuracy.Fig. 5 a, Fig. 5 b show respectively with first metric function and carry out plateau phenomenon, the burr phenomena that frame detects and regularly occurs synchronously, and wherein abscissa is represented the sampling instant value, and ordinate is represented the first metric function value.For fear of the plateau phenomenon and the burr phenomena of first metric function, need do further processing to first metric function.

Step 24: above-mentioned first metric function added up obtains second metric function, and the length of this accumulating operation is circulating prefix-length CP-Length;

The reason that produces plateau phenomenon owing to first metric function is that Cyclic Prefix has and the duplicating of lead code useful symbol end part, at additive white Gaussian noise (Additive White GaussianNoise, hereinafter to be referred as AWGN) under the situation, the land lengths of first metric function equals the length of Cyclic Prefix, therefore, utilize this improved properties first metric function, first metric function is passed through, accumulation length is the slip accumulator of circulating prefix-length, obtain second metric function, carry out frame detection and regularly synchronous with second metric function.

Therefore, the second metric function MT (d) is: $\mathrm{MT}\left(d\right)=\underset{i=0}{\overset{\mathrm{CP}-\mathrm{Length}-1}{\mathrm{\Σ}}}M(d+i)$

Fig. 6 a is under the awgn channel high s/n ratio situation, and the schematic diagram of first metric function, Fig. 6 b are under the awgn channel high s/n ratio situation, the schematic diagram of second metric function; Fig. 7 a is under the awgn channel low signal-to-noise ratio situation, and the schematic diagram of first metric function, Fig. 6 b are under the awgn channel low signal-to-noise ratio situation, the schematic diagram of second metric function.Wherein the abscissa among Fig. 6 a, Fig. 6 b, Fig. 7 a, Fig. 7 b is all represented the sampling instant value, and ordinate is all represented corresponding metric function value.As can be seen, second metric function only has a peak from Fig. 6 a, Fig. 6 b, the plateau phenomenon that first metric function occurs do not occur; From Fig. 7 a, Fig. 7 b as can be seen, second metric function is very level and smooth, the burr phenomena that first metric function occurs do not occur.

Step 25: by numerical value and threshold value λ with second metric function _fRelatively, carry out frame and detect, promptly the numerical value when second metric function surpasses threshold value λ _fThe time, expression receives a frame;

From Fig. 7 b as can be seen, second metric function has been eliminated the burr phenomena of first metric function effectively, therefore, under the certain situation of false dismissed rate, reduced the false alarm probability that frame detects, Fig. 8 shows under the certain situation of false dismissed rate, the comparison diagram of false alarm rate when utilizing first metric function and second metric function to carry out the frame detection, the longitudinal axis is represented false alarm rate, transverse axis is represented signal to noise ratio snr (dB of unit), as can be seen from Figure 8, utilizes second metric function to carry out frame and detects, with utilize first metric function to carry out frame to detect and to compare, can effectively reduce the false alarm rate that frame detects.

Step 26: the numerical value of determining second metric function surpasses threshold value λ _fAfter peak time corresponding position n0, and the position after this time location n0 postponed is as the timing sync bit, this delay is no more than circulating prefix-length.

From Fig. 6 a, Fig. 6 b as can be seen, the peak of second metric function is the position that the first metric function platform begins, and accurate timing sync bit (position of the useful sign-on of OFDM lead code) is the platform end position in theory, therefore, the peak time corresponding position of second metric function is postponed circulating prefix-length backward, be ideally accurate timing sync bit.Simultaneously, according to the characteristics of ofdm system, regularly sync bit is as long as within Cyclic Prefix, be allowed to, therefore, the peak time corresponding position n0 of second metric function being moved a distance that is no more than circulating prefix-length backward, all is feasible.But, under fading channel, because the influence of multipath, the land lengths of first metric function can not equal circulating prefix-length just, but less than circulating prefix-length, in this case, if still delay circulating prefix-length as the timing sync bit, can cause regularly sync bit to fall into the useful symbolic component of lead code, cause regularly loss, in this case, spacing after moving is less than circulating prefix-length, can select to move backward half of Cyclic Prefix, promptly moves half position of circulating prefix-length backward with the peak time corresponding position of second metric function, as the timing sync bit, promptly regularly sync bit n1 is: n1=n0+CP-Length/2.

Lead code in the present embodiment has the segmentation repeat property, can be multistage, and be not limited only to three sections above-mentioned repeat property, and the calculating principle during multistage is with the principle among the above-mentioned embodiment.

Present embodiment, by first metric function being carried out the computing that accumulation length is a circulating prefix-length, obtain second metric function, second metric function has been eliminated the plateau phenomenon and the burr phenomena of first metric function, improved the precision that frame detects and timing is synchronous, and on the false dismissed rate basis of invariable, reduced the false alarm probability that frame detects.

Fig. 9 is the structural representation of one time of embodiment of the invention synchronizer, and this embodiment comprises: processing module 1, accumulator module 2 and frame detect and timing synchronization module 3; Processing module 1 is used for carrying out to received signal auto-correlation processing and calculating energy and handles, and obtains first metric function, and described first metric function characterizes the auto-correlation degree of described received signal; Accumulator module 2, being used for this first metric function added up obtains second metric function; Frame detects and timing synchronization module 3, is used for carrying out frame according to this second metric function and detects with regularly synchronously.

Figure 10 is the structural representation of the embodiment of the invention two time synchronism apparatus, and than embodiment shown in Figure 9, among this embodiment, processing module 1 specifically comprises: receiving element 11, energy and correlation unit 12, normalizing unit 13; Receiving element 11 is used to receive first received signal, and after the segments of the block sampling number of first received signal time-delay lead code subtracted one times, second received signal that receives; Energy and correlation unit 12 are used to calculate energy, the energy of second received signal and the auto-correlation function of first received signal and second received signal of first received signal that receiving element 11 receives; Normalizing unit 13, be used for the auto-correlation function of energy and correlation unit 12 outputs is asked computing module-square, and will ask value behind the computing module-square with the product of the energy of the energy of first received signal of energy and correlation unit 12 outputs and second received signal, carry out the normalization computing, obtain first metric function, and export this first metric function to accumulator module 2.

As shown in figure 11, receiving element 11 further comprises: time-delay subelement 111 and reception subelement 112; Time-delay subelement 111 is used to receive first received signal, and the segments of the block sampling number of the lead code of time-delay received signal subtracts one times (if lead code has N section repeat property, every section hits is L, then the segments of lead code is N, the block sampling number is L, and time-delay is L hits of (N-1) * so); Receiving subelement 112 is used for receiving second received signal after time-delay subelement 111 delay process.Energy and correlation unit 12 further comprise: first quantum of energy unit 121, second quantum of energy unit 122, conjugation subelement 123 and correlator unit 124; First quantum of energy unit 121 is used to calculate the energy of first received signal that time-delay subelement 111 receives; Second quantum of energy unit 122 is used to calculate the energy of second received signal that receives subelement 112 receptions; Conjugation subelement 123 is used for that first received signal that time-delay subelement 111 receives is carried out conjugation to be handled; Correlator unit 124 is used for the conjugated signal of conjugation subelement 123 outputs is carried out relevant treatment with second received signal that receives subelement 112 receptions, obtains the auto-correlation function of received signal.Normalizing unit 13 further comprises: mould square subelement 131, the subelement 132 and the subelement 133 that is divided by multiply each other; Mould square subelement 131 is used for the auto-correlation function of correlator unit 124 outputs is asked computing module-square; The subelement 132 that multiplies each other is used to calculate the product of the energy of first quantum of energy unit 121 and 122 outputs of second quantum of energy unit; The subelement 133 that is divided by is used for obtaining first metric function according to the signal of the signal of conjugation subelement 123 outputs and subelement 132 outputs of multiplying each other, promptly the signal of exporting with the signal removal mould square subelement 131 of subelement 132 outputs of multiplying each other obtains first metric function, and exports accumulator module to.

Frame detects and timing synchronization module 3 specifically comprises: frame detecting unit 31, timing lock unit 32; Frame detecting unit 31 is used to receive second metric function that accumulator module 2 is exported, and the value and the threshold value of second metric function compared, and carries out frame and detects, and when the numerical value of described second metric function surpassed threshold value, then expression received a frame; Timing lock unit 321, the numerical value of second metric function that is used for determining that frame detecting unit 31 receives surpasses the peak time corresponding position after the threshold value, and this time location delayed a spacing that is no more than circulating prefix-length, as the timing sync bit.

In the present embodiment, the spacing of time-delay subelement time-delay is the hits of segmentation with lead code of segmentation repeat property, the hits length of the calculating energy of the hits of the relevant treatment of correlator unit, first quantum of energy unit and second quantum of energy unit is (segments-1) * block sampling number, the length that accumulator module adds up is the length of Cyclic Prefix, and regularly the spacing delayed of lock unit can be half of circulating prefix-length.

Present embodiment, by first metric function being carried out the computing that accumulation length is a circulating prefix-length, obtain second metric function, second metric function has been eliminated the plateau phenomenon and the burr phenomena of first metric function, improved the precision that frame detects, and on the false dismissed rate basis of invariable, reduced the false alarm probability that frame detects.

It should be noted that at last: above embodiment only in order to the technical scheme of the explanation embodiment of the invention, is not intended to limit; Although the embodiment of the invention is had been described in detail with reference to previous embodiment, those of ordinary skill in the art is to be understood that: it still can be made amendment to the technical scheme that aforementioned each embodiment put down in writing, and perhaps part technical characterictic wherein is equal to replacement; And these modifications or replacement do not make the essence of appropriate technical solution break away from the spirit and scope of each embodiment technical scheme of the embodiment of the invention.

Claims (13)

1, a kind of method for synchronizing time is characterized in that, comprising:

Carry out auto-correlation processing and calculating energy to received signal and handle, obtain first metric function, described first metric function characterizes the auto-correlation degree of described received signal;

Described first metric function added up obtain second metric function;

Carrying out frame according to described second metric function detects with regularly synchronously.

2, method for synchronizing time according to claim 1 is characterized in that, described auto-correlation processing and the calculating energy of carrying out to received signal handled, and obtains first metric function and comprises:

First received signal that receives is carried out delay process;

Obtain the energy of first received signal according to first received signal; Obtain the energy of second received signal according to second received signal that receives after the time-delay; First received signal and second received signal are carried out relevant treatment, obtain the auto-correlation function of received signal;

Described auto-correlation function is asked mould square, and carry out normalization with the energy of the energy of described first received signal and second received signal and obtain first metric function.

3, method for synchronizing time according to claim 2 is characterized in that, the time-delay hits that described first received signal that will receive is carried out delay process is: the block sampling number of the lead code of received signal;

The hits of described relevant treatment and calculating energy is that the segments of the block sampling number of described lead code subtracts one times.

4, method for synchronizing time according to claim 1, the described accumulation length that described first metric function is added up is the length of Cyclic Prefix.

5, method for synchronizing time according to claim 1 is characterized in that, describedly carries out frame according to second metric function and detects and to be specially:

When the numerical value of described second metric function surpassed threshold value, then expression received a frame.

6, method for synchronizing time according to claim 1 is characterized in that, describedly carries out timing according to second metric function and is specially synchronously:

The numerical value of described second metric function is postponed above the peak time corresponding position after the threshold value, and the time location after this postpones is regularly a sync bit.

7, method for synchronizing time according to claim 6 is characterized in that, the described length that the second metric function peak time corresponding position is postponed to be less than or equal to Cyclic Prefix.

8, method for synchronizing time according to claim 6 is characterized in that, described the second metric function peak time corresponding position is postponed the length of half Cyclic Prefix.

9, a kind of time synchronism apparatus is characterized in that, comprising:

Processing module is used for carrying out to received signal auto-correlation processing and calculating energy and handles, and obtains first metric function, and described first metric function characterizes the auto-correlation degree of described received signal;

Accumulator module, being used for described first metric function added up obtains second metric function;

Frame detects and the timing synchronization module, is used for carrying out frame according to described second metric function and detects with regularly synchronously.

10, time synchronism apparatus according to claim 9 is characterized in that, described processing module comprises:

Receiving element is used for first received signal that receives is carried out delay process, and receives second received signal after time-delay;

Energy and correlation unit are used to calculate the energy of described first received signal and the energy of second received signal, and calculate the auto-correlation function of described first received signal and second received signal;

The normalizing unit is used to calculate the mould square of described auto-correlation function, and carries out normalization with the energy of described first received signal and the energy of second received signal, obtains first metric function.

11, time synchronism apparatus according to claim 9 is characterized in that, described frame detects and the timing synchronization module comprises:

The frame detecting unit is used to receive described second metric function, and described second metric function and threshold value are compared, and carries out frame and detects, and when the numerical value of described second metric function surpassed threshold value, then expression received a frame;

Regularly lock unit is used for the numerical value of described second metric function is postponed above the peak time corresponding position after the threshold value, and the time location after this postpones is regularly a sync bit.

12, time synchronism apparatus according to claim 11 is characterized in that, described delay length is less than or equal to the length of Cyclic Prefix.

13, time synchronism apparatus according to claim 9 is characterized in that, the described accumulation length that first metric function is added up is the length of Cyclic Prefix.

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