CN101039300A - Synchronous timing method - Google Patents

Abstract

The present invention discloses a method of synchronous timing, which includes steps as follows: step 1, eliminate the randomicity of the phase reference code element received through eliminating the disturbance of the phase reference code element received and doing auto correlation of the data after disturbance elimination; step 2, search and determinate the accurate maximal correlation value by utilizing the correlation characteristic of the phase reference code element; step 3, put correlative mathematic operation on the maximal correlation value, adjust time benchmark, and finish the synchronous timing. The present invention provides a fast and accurate method for synchronous timing by utilizing the correlation characteristic of the phase reference code element, which achieves the purpose of simplifying algorithm and enhancing the performance.

Description

A kind of method of synchronization timing

Technical field

This invention relates to a kind of method for synchronous in OFDM (OFDM, OrthogonalFrequency Division Multiplexing) communication, is specifically related to the method that the symbol timing offset detects between receiver and the transmitter.

Background technology

DAB (Digital Audio Broadcasting, digital audio broadcasting) system is by ETSI (European Telecommunications Standards Institute, ETSI) a kind of digital audio broadcast system of Ti Chuing, the modulation system that it adopts OFDM (OrthogonalFrequency Division Multiplexing, orthogonal frequency division multiplexi) to combine with DQPSK (difference quadrature phase shift keying modulation).

Simultaneous techniques comprises time synchronized (sign synchronization, frame synchronization) and Frequency Synchronization.Because data are the unit transmission with the frame, must determine the original position of each frame exactly, system just can communicate by letter reliably.Therefore, time synchronized is as synchronous primary link, and the accuracy of its estimation will directly influence the accuracy of Frequency Synchronization.Synchronization timing all is basic task for any digital communication system, does not have accurate synchronized algorithm just can not the data that transmit to be received reliably.

Symbol in the ofdm system regularly (Symbol Timing) is meant the accurate moment of trying to achieve single OFDM sign-on and end.Symbol result regularly will determine the window of FFT, and decision just is used to calculate one group of sampling value that each receives the OFDM symbol.Receiving terminal need find the starting point of each OFDM symbol correctly to carry out the FFT demodulation in the data flow that receives by the symbol timing algorithm before subcarrier is carried out demodulation.In multipath channel; surpass protection symbol timing error at interval and can cause intersymbol interference (Inter-Symbol Interference; ISI), destroy sub-carrier orthogonality and reduce systematic function, that is to say that the sign synchronization deviation directly influences the anti-multipath effect capability of ofdm system.

Owing between the OFDM symbol, inserted Cyclic Prefix (Cyclic Prefix; CP) protection at interval; therefore the initial moment of OFDM timing synchronization can change in protection at interval, and can not cause intersymbol interference ISI and inter-carrier interference ICI (Inter-CarrierInterference).Have only when FFT computing window to have exceeded character boundary, ISI and ICI just can be caused in the amplitude that perhaps the falls into symbol interval of roll-offing.Therefore, ofdm system is looser relatively to the requirement meeting of timing synchronization, but in multi-path environment, in order to obtain best systematic function, needs to determine best symbol regularly.

Under additive white Gaussian noise (AWGN) channel condition; the sign synchronization deviation to the influence of FFT output symbol is: if the symbol original position of estimating is positioned at protection at interval; FFT output sub-carrier signal in each symbol can be with different phase angle upsets, and this phase angle and synchronism deviation are proportional.If the symbol original position of estimating is positioned at data break, the OFDM symbol of so current sampling will comprise some other OFDM symbol sampler points.Like this, each symbol subcarrier of FFT output all can be owing to intersymbol interference causes phase overturn or dispersion.The phase overturn that the sign synchronization deviation causes can be proofreaied and correct by signal that suitably upset receives on phase place, but the dispersion of the signal constellation which that is caused by ISI has produced bit error rate (BER).In addition, also must consider the influence of channel.Because multipath effect, the OFDM symbol is disperseed on time shaft, is used for the protection of estimate symbol sync bit at interval owing to be subjected to the interference of last symbol, thereby has influenced synchronous estimation.

The needed single-frequency point networking of DAB system (Single Frequency Network, characteristic SFN) can cause receiver having bigger multidiameter and the deep fade on the frequency domain on the time domain; In addition, receiver need be supported signal demodulation under the situation of high-speed mobile; When carrying out the regularly accurate estimation of symbol, can't obtain carrier synchronization condition accurately, so frequency shift (FS) can cause the phase deviation of OFDM symbol on the time domain again.These problems of more than enumerating all cause the measurement of symbol timing deviation to become a difficult point.

Traditional method for synchronizing time can't solve above-mentioned all problems, or it is too big to solve the computing too complex or the power consumption of above-mentioned all problem.The Measurement Algorithm of the symbol timing deviation that the present invention proposes can overcome above all problems, and the effect brilliance, hardware complexity is low and low-power consumption.

Summary of the invention

The present invention proposes a kind of time synchronization method that adopts adjacent carrier wave PRS (PhaseReference Symbol) coherent detection to realize low-power consumption, quick symbol timing deviation search under the low signal-to-noise ratio condition.The present invention has utilized the characteristic of PRS, and frequency deviation searching accuracy height, algorithm are simple, has reached the purpose that improves performance.

The inventive method comprises the steps:

Step 1: by the phase reference code that receives being gone disturb and to the data auto-correlation after going to disturb, to eliminate the randomness of the described phase reference code that receives;

Step 2: utilize the search of phase reference code correlation properties and determine accurate maximum related value;

Step 3: to the mathematical operation of being correlated with of described maximum related value, adjust time reference, finish synchronization timing.

Further, described step 1 specifically comprises the steps:

Step 1.1: the phase reference code that receives is carried out Fourier transform, obtain the frequency domain phase reference code;

Step 1.2: by frequency domain phase reference code and local PRS conjugate multiplication are gone to disturb operation.

Further, described step 2 specifically comprises the steps:

Step 2.1: carry out correlation peaks by peak detector and detect, find the maximum related value peak value;

Step 2.2: the synchronization decisions device is repeatedly searched for described maximum related value peak value, up to finding accurate maximum related value.

Further, described step 3 specifically comprises the steps:

Step 3.1: enable described maximum related value is asked the step of argument, convert the phase deviation of described maximum related value to time deviation by mathematical conversion;

Step 3.2: calculate the real time benchmark according to described time deviation and contrast the Preset Time benchmark, if align with the Preset Time benchmark, then described Preset Time benchmark is correct, if than Preset Time benchmark in advance or delay, then adjust, finish synchronization timing.

According to different orthogonal frequency division multiplexi systems, the inventive method sub-carriers postpones the best value of number should be minimum.

The inventive method only need rather than be carried out frequency deviation in time domain and detect at frequency domain, and the effective precondition of algorithm satisfies easily; The inventive method need not the point by point search frequency deviation, and search speed is fast; The inventive method has utilized the characteristic of phase reference code to carry out the frequency deviation search fully, and therefore search is accurate, and algorithm is more accurately simple than additive method.

Description of drawings

Fig. 1 is the flow chart of steps of the inventive method;

Fig. 2 is the theory diagram of the inventive method;

Fig. 3 is the explanation schematic diagram of adjacent sub-carriers phase cross-correlation;

Fig. 4 is the schematic diagram of the inventive method register stage;

Fig. 5 is a schematic diagram data of using the simulation result of the inventive method.

Embodiment

Below in conjunction with the drawings and specific embodiments the present invention is elaborated.Carrier wave frequency deviation is counted n and is got 16 in the present embodiment, and promptly the hunting zone is-16～+ 16, and searching times is 33 times; Present embodiment postpones sub-carrier number d and gets 1 at the DAB system, and promptly adjacent subcarrier is relevant mutually.Structure of the present invention and effect describe as just present embodiment, and technological thought of the present invention and core constitute and effect is not limited thereto.

Fig. 1 is the flow chart of steps of the inventive method.As shown in Figure 1, the inventive method comprises the steps: step 1, by the phase reference code that receives being gone disturb and to the data auto-correlation after going to disturb, to eliminate the randomness of the described phase reference code that receives; Step 2 is utilized the search of phase reference code correlation properties and is determined accurate maximum related value; Step 3 to the mathematical operation of being correlated with of described maximum related value, is adjusted time reference, finishes synchronization timing.

Fig. 2 is a theory diagram of the present invention, and enforcement principle of the present invention as shown in Figure 2 is as follows: time domain PRS obtains frequency domain PRS through the FFT conversion; With frequency domain PRS and local PRS conjugate multiplication, remove scrambler; Frequency domain PRS after going to disturb is postponed d subcarrier, carry out auto-correlation with described frequency domain PRS after going to disturb again; Carry out correlation peaks by peak detector and detect, find the maximum related value peak value; The synchronization decisions device is counted the searching times that n controls peak detector by carrier wave frequency deviation, and determines maximum related value through repeatedly searching for; If maximum related value then enables the step of phase-detection, convert the phase deviation of described maximum related value to time deviation by mathematical conversion then; Calculate the real time benchmark according to described time deviation and contrast the Preset Time benchmark, if align with the Preset Time benchmark, then described Preset Time benchmark is correct, if than Preset Time benchmark in advance or delay, then adjust, finishes synchronization timing.

When d got 1, each adjacent sub-carrier was done auto-correlation.Fig. 3 is the explanation schematic diagram of adjacent sub-carriers phase cross-correlation.As shown in Figure 3, subcarrier 1 is done auto-correlation with subcarrier 2, and subcarrier 2 is done auto-correlation with subcarrier 3 ... subcarrier 14 is done auto-correlation with subcarrier 15, and subcarrier 15 is done auto-correlation with subcarrier 16.Strengthened the ability of anti-multipath effect like this.

Fig. 4 is the schematic diagram of the inventive method register stage.As shown in Figure 4, register stage embodiment of the present invention is as follows: the PRS of the reception after FFT handles is the center with the dc point position, (intercepted length is that 32 integral multiple adds 1 to one section regular length subcarrier of intercepting sequence of symmetry, intercepted length depends on the performance of algorithm requirement, 256+1 subcarrier for example), remove behind the dc point each subcarrier conjugate multiplication, the promptly relevant processing procedure of disturbing of going with the local PRS sequence of the corresponding length of local storage; Local PRS sequence is subjected to the control of synchronization decisions device, and the starting point of each intercepting is subcarrier slip one by one from left to right, and the border start point/end point of slip scan depends on the scope that frequency deviation detects, and the hunting zone is-16-+16 in the present embodiment; PRS is correlated with and goes to disturb the sequence of handling back formation is the adjacent subcarrier autocorrelator of 32 subcarrier spans through a length, makes per 32 subcarriers carry out the adjacent stack again of being correlated with of neighbour, asks absolute value then, adds up by accumulator at last; All calculates on all frequency deviations search point and finish, peak detector carries out the peak value detection, and the position during corresponding peak value accumulated value is the maximum related value peak value; The effect of synchronization decisions is to differentiate whether the value of gained is maximum related value, if maximum related value then enables this value is asked the step of its argument; Then with argument divided by 2 π d/k, convert the phase deviation of described maximum related value to time deviation; Calculate the real time benchmark according to described time deviation and contrast the Preset Time benchmark, if align with the Preset Time benchmark, then described Preset Time benchmark is correct, if than Preset Time benchmark in advance or delay, then adjust, finishes synchronization timing.

Fig. 5 is a schematic diagram data of using the simulation result of the inventive method.By shown in Figure 5, TU-6 channel in pattern 1 (typical urban area) down during signal to noise ratio snr=4dB, is set a symbol offset every 3 symbols.As shown in Figure 5, the symbol offset number of transverse axis for setting, the longitudinal axis is detected symbol offset number.As seen from Figure 3, locate to detect accurately, locate at 17 to occur+slight error of 1 sampled point at 11 and 14.If each detect all accurately, analogous diagram should be a diagonal angle straight line, and emulation detects display result almost near error-free results, verifies out that thus application method provided by the invention can obtain the symbol timing offset exactly.

Further, the specific algorithm of the inventive method is as follows.

In the methods of the invention, frequency domain PRS can be write as:

R=PHexp (θ) (formula 1)

R=[R (1) ..., R (k)] be the frequency domain PRS after the experience FFT conversion; P is a frequency domain PRS sequence of vectors; H is the frequency response of channel, supposes not have interference of noise herein; θ is the phase shift that carrier wave frequency deviation (Carrier Frequency Offset) and timing slip (Timing Offset) cause.Described timing slip is meant sample because the inconsistent deviation that causes of starting point; Described carrier wave frequency deviation is meant the deviation of carrier phase.For each subcarrier, θ can be write as:

θ _k=(2 π k/K) n _o+ θ _o(formula 2)

θ _oBe the initial phase shift on each carrier wave, think θ herein _oOnly produce by decimal times carrier wave frequency deviation; (the n of 2 π/K) _oBe the phase shift that causes by timing slip, wherein n ₀Be the timing slip hits, k is the carrier wave sequence number, and K is a carrier number.

At first with the conjugation P of frequency domain PRSR (k) with local PRSP (k) ^*(k) multiply each other.When the integer-time carrier wave frequency deviation location finding was correct, P (k) can be cancelled.Local PRS is defined as:

Wherein, L represents frame number; K represents subcarrier number;

 _KBy i, k, k ', the n decision of tabling look-up.Because each subcarrier of PRS only may be+1 ,-1 ,+j, so-j is P (k+n) P ^*(k)=1.

Therefore, can get by (formula 1) and (formula 2):

D _n(k)＝R(k+n)·P ^*(k)

＝P(k+n)H(k+n)exp(2π(k+n)n _o/K+θ _o)·P ^*(k)

=H (k+n) exp (2 π (k+n) n _o/ K+ θ _o) (formula 4)

Above process is called as disturbs D _n(k) signal after representative goes to disturb.

Then to the signal D after going to disturb _n(k) and the carrier wave sequence that postpones d carrier wave carry out auto-correlation, that is:

$M\left(n\right)=\underset{k=1}{\overset{K}{\mathrm{\Σ}}}{D}_n\left(k\right)\·{\left(D_n(k-d)\right)}^{*}$

$=\underset{k=1}{\overset{K}{\mathrm{\Σ}}}(R(k+n)\·P^{*}\left(k\right))\·{(R(k+n-d)\·P^{*}(k-d))}^{*}$

(formula 3)

When the integer-time carrier wave frequency deviation location finding is correct,, can continue (formula 3) to be write as by (formula 4):

$M\left(n\right)=\underset{k=1}{\overset{K}{\mathrm{\Σ}}}{D}_n\left(k\right)\·{\left(D_n(k-d)\right)}^{*}$

$=\underset{k=1}{\overset{K}{\mathrm{\Σ}}}(R(k+n)\·P^{*}\left(k\right))\·{(R(k+n-d)\·P^{*}(k-d))}^{*}$

$=\underset{k=1}{\overset{K}{\mathrm{\Σ}}}\left(H(k+n)\exp (2\mathrm{\π}(k+n)n_o/K+{\mathrm{\θ}}_o)\right)\·{\left(H(k+n-d)\exp (2\mathrm{\π}(k+n-d)n_o/K+{\mathrm{\θ}}_o)\right)}^{*}$

$=\underset{k=1}{\overset{K}{\mathrm{\Σ}}}\left(H(k+n)H^{*}(k+n-d)\exp (2\mathrm{\πd}{n}_o/K)\right)$

When baseband signal bandwidth during much smaller than channel width, the flat decline of signal experience; When baseband signal bandwidth is very big, the experience frequency selective fading.Can make H (k+n) and H (k+n-d) on the bandwidth of same flat decline (Flat Fading) when d is small enough to, just can avoid the frequency selective fading in the channel this moment, promptly the value of H (k+n) and H (k+n-d) is almost equal at this moment.So, following formula can be write as

$M\left(n\right)=\underset{k=1}{\overset{K}{\mathrm{\Σ}}}\left({\left|H(k+n)\right|}^2\exp (2\mathrm{\πd}{n}_o/K)\right)$

(formula 5)

As can be known concerning the part of each conjugate multiplication, phase shift all is exp (2 π dn from formula 5 ₀/ K).As previously mentioned, this part phase shift is caused by timing slip, and it is same value concerning each auto-correlation part.Therefore, the phase shift theta that causes of the phase shift that on different carrier, produces of described timing slip and decimal times carrier wave frequency deviation _oCan utilize auto-correlation to eliminate.

The maximum of counting n search correlation M (n) by the change carrier wave frequency deviation is max{M (n) }, just can realize estimation to maximum related value.

To described maximum related value max{M (n) } ask argument:

arg{max{M(n)}}＝2πdn _o/K

Divided by 2 π d/k, gained is timing slip hits n with described argument _o:

n _o＝arg{max{M(n)})/(2πd/K)

Described max{M (n) } be a plural number, its argument becomes certain ratio with synchronism deviation, so obtaining max{M (n) } ask its argument can arrive the hits n of symbol offset afterwards _oThe hits of the symbol offset of present frame is exactly the side-play amount of current timing with the result's of former frame difference, carries out the debugging of time reference based on this difference, and synchronization timing is finished.

The inventive method is not limited to and is used for the DAB system, and all use system's this method of OFDM technology all to be suitable for.As in the DAB system, because PRS occupies all effective carrier waves, subcarrier postpones number and gets 1 the best.And be in the DVB system of an effective carrier wave part at PRS, subcarrier postpones number and is set as 2 interval minimum values between the most close pilot frequency carrier wave usually.

The above is the specific embodiment of the present invention only, and is not used in qualification the present invention.Any replacement, combination, discrete all should being included within protection scope of the present invention of the present invention being made step well know in the art.

Claims (5)

1. the method for a synchronization timing is characterized in that comprising the steps:

Step 1: by the phase reference code that receives being gone disturb and to the data auto-correlation after going to disturb, to eliminate the randomness of the described phase reference code that receives;

Step 2: utilize the search of phase reference code correlation properties and determine accurate maximum related value;

Step 3: to the mathematical operation of being correlated with of described maximum related value, adjust time reference, finish synchronization timing.

2. the method for a kind of synchronization timing according to claim 1 is characterized in that, described step 1 comprises further:

Step 1.1: the phase reference code that receives is carried out Fourier transform, obtain the frequency domain phase reference code;

Step 1.2: by frequency domain phase reference code and local PRS conjugate multiplication are gone to disturb operation;

Step 1.3: the frequency domain phase reference code after will going to disturb carries out auto-correlation by correlator.

3. the method for a kind of synchronization timing according to claim 1 is characterized in that, described step 2 comprises further:

Step 2.1: carry out correlation peaks by peak detector and detect, find the maximum related value peak value;

Step 2.2: the synchronization decisions device is repeatedly searched for described maximum related value peak value, up to finding accurate maximum related value;

4. the method for a kind of synchronization timing according to claim 1 is characterized in that, described step 3 comprises further:

Step 3.1: enable described maximum related value is asked the step of argument, convert the phase deviation of described maximum related value to time deviation by mathematical conversion;

Step 3.2: calculate the real time benchmark according to described time deviation and contrast the Preset Time benchmark, if align with the Preset Time benchmark, then described Preset Time benchmark is correct, if than Preset Time benchmark in advance or delay, then adjust, finish synchronization timing.

5. the method for a kind of synchronization timing according to claim 1 is characterized in that: according to different orthogonal frequency division multiplexi systems, described synchronization timing method sub-carriers postpones the best value of number should be minimum.

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