CN102123128B - Blind timing synchronization method based on circular structure - Google Patents

Abstract

The invention discloses a blind timing synchronization method based on a circular structure, comprising the following steps: firstly, performing Discrete Fourier Transformation (DFT) on N points by respectively taking the ith to the (i+G)th sample points of a receiving signal as start points; after phase compensation, performing Inverse Discrete Fourier Transformation (IDFT) to obtain G+1 time domain sequences; then calculating the differences between adjacent time domain sequences and the average values of the difference values; and finally searching the minimum average value in an observation window, and giving out the corresponding timing synchronization estimation. In the method provided by the invention, an OFDM (Orthogonal Frequency Division Multiplexing) symbol is added to a circular structure formed after circular prefix, and the differences between the sequences after phase compensation are calculated to acquire the timing synchronization information of the system without the assist of training sequence or pilot frequencies; a large amount of Fourier positive/reverse transformation are used, so that the implementation complexity of the system is reduced; and simultaneously, the blind channel length estimation method provided by the invention can be used for various block transmission systems with circular prefix containing OFDM.

Description

A kind of blind time synchronization method based on loop structure

Technical field

The present invention relates to the simultaneous techniques in the mobile communication, relate in particular to a kind of blind time synchronization method that is applied to OFDM (hereinafter to be referred as OFDM) system.

Background technology

Regularly be the prerequisite of mobile communication system energy proper communication synchronously.In order to support high-speed data service, future mobile communication system will adopt the system of broadband, many (sending and receiving) antenna, and OFDM is the important candidate scheme of future mobile communication system.When having known frequency pilot sign of receiving terminal or training sequence in the ofdm system, can adopt such as methods such as auto-correlation, maximum likelihoods, the timing of carrying out system is synchronous.In order to improve spectrum efficiency, in some ofdm systems, there are not training sequence or frequency pilot sign, the timing of these systems need be adopted blind method synchronously.In order to eliminate intersymbol interference (hereinafter to be referred as ISI), Cyclic Prefix all will be inserted in each OFDM symbol front.Duplicating of Cyclic Prefix is-symbol afterbody, and greater than the expansion of the maximum delay of multidiameter fading channel.

Summary of the invention

Goal of the invention:, the invention provides the blind time synchronization method that a kind of fast and reliable, estimated accuracy height, implementation complexity are low, be applicable to ofdm system in order to overcome the deficiencies in the prior art.

Technical scheme: for achieving the above object, the technology that the present invention adopts is put case and is:

A kind of blind time synchronization method based on loop structure comprises the steps:

1) respectively with the i of received signal, i+1, K, i+G sampled point are the discrete Fourier transform (DFT) (hereinafter to be referred as DFT) that starting point is carried out N and ordered, the frequency-region signal that to obtain G+1 length be N;

2) each subcarrier to each frequency-region signal carries out the respective phase compensation by side-play amount and subcarrier sequence number;

3) frequency-region signal after the compensation is done N the inverse discrete fourier transform of putting (hereinafter to be referred as IDFT), obtain G+1 time domain sequences;

4) calculate the mean error of former and later two continuous time domain sequences, obtain G mean error value;

5) mean value of G mean error value of calculating is designated as M (i);

6) the pairing i of M (i) of minimum in the watch window, i is the sync bit of OFDM symbol;

Wherein, i is any one sampling location of received signal in the observation window; N is the sub-carrier number of ofdm system; G is the length of Cyclic Prefix, and G is greater than the maximum delay expansion of wireless multipath fading channel usually.

Beneficial effect: a kind of blind time synchronization method provided by the invention based on loop structure, utilize the OFDM symbol to add the loop structure that forms behind the Cyclic Prefix, by calculating difference through the front and back sequence after the phase compensation, can be in the auxiliary timing synchronizing information of acquisition system down without any training sequence or pilot tone; Fourier just/inverse transformation exists implementation structure and algorithm efficiently fast, this method by adopt a large amount of Fouriers just/inverse transformation, alleviated system and realized complicated; Simultaneously, the blind Channel length method of estimation of the present invention's proposition can be used to comprise the various block transmission systems that Cyclic Prefix is arranged of OFDM.

Description of drawings

Fig. 1 is a flow chart of the present invention;

Fig. 2 is for realizing the apparatus structure schematic diagram of the inventive method.

Embodiment

Below in conjunction with accompanying drawing the present invention is done further explanation.

Be illustrated in figure 1 as a kind of blind time synchronization method based on loop structure, it comprises the steps:

1) respectively with the i of received signal, i+1, K, i+G sampled point is that starting point is carried out the DFT conversion that N is ordered, the frequency-region signal that to obtain G+1 length be N;

2) each subcarrier to each frequency-region signal carries out the respective phase compensation by side-play amount and subcarrier sequence number;

3) frequency-region signal after the compensation is done N IDFT conversion of putting, obtain G+1 time domain sequences;

4) calculate the mean error of former and later two continuous time domain sequences, obtain G mean error value;

5) mean value of G mean error value of calculating is designated as M (i);

6) the pairing i of M (i) of minimum in the watch window, i is the sync bit of OFDM symbol;

Wherein, i is any one sampling location of received signal in the observation window; N is the sub-carrier number of ofdm system; G is the length of Cyclic Prefix, and G is greater than the maximum delay expansion of wireless multipath fading channel usually.

Said method can utilize device shown in Figure 2 to realize.

Suppose that a number of sub carrier wave that ofdm system comprised is N, the length of Cyclic Prefix is G.According to method shown in Figure 1, i with received signal is starting point to i+G sampled point at first respectively, carries out the DFT conversion that N is ordered; After phase compensation, be sent to the inverse discrete fourier transform device, obtain G+1 time domain sequences; Then, calculate the difference of adjacent time domain sequences, and the average of these differences; At last,, seek minimum average, and provide corresponding timing and estimate synchronously by minimum value searcher in the window.

Concrete grammar is described below:

I sampled point with received signal is starting point, and after N DFT conversion of putting, its frequency-domain expression can be write as:

$Y^i\left(k\right)=H\left(k\right)X\left(k\right){\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="HDA0000049777680000011.png"\; state="\{\{state\}\}">e</figure-callout>}}^j+V\left(k\right),k=\mathrm{0,1},K,N-1$ [formula one]

Wherein, k represents the subcarrier sequence number; n _εExpression timing error, and n _ε≤ i≤n _ε+ G; V (k) represents additive white Gaussian noise; H (k) is the frequency domain response of channel, can be expressed as:

$H\left(k\right)=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}h\left(l\right)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA0000049777680000011.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}\frac{k{\mathrm{\&tau;}}_l}{\mathrm{NT}}}$ [formula two]

Here T represents the sampling period, τ _lRepresent the time delay in l root footpath, L represents the distinguishable footpath of channel number.

To the Y after the phase compensation ⁱ(k) do the IDFT conversion of N point, obtain corresponding time-domain signal and be:

$r^i\left(n\right)=\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{Y}^i\left(k\right)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA0000049777680000011.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;}}{N}k(i-G)}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="HDA0000049777680000011.png"\; state="\{\{state\}\}">e</figure-callout>}}^j,n=\mathrm{0,1},K,N-1$ [formula three]

Be starting point with the i+1 of received signal to i+G sampled point respectively again, repeat the process of [formula one], [formula two] and [formula three], obtain G+1 sequence, each sequence has N element, that is:

r ^m=[r ^m(0), r ^m(1), K, r ^m(N-1)], m=i, i+1, K, i+G [formula four]

Calculate the mean error of former and later two continuous time domain sequences, that is:

$\mathrm{\&sigma;}\left(t\right)=\frac{1}{N}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}|r^t\left(n\right)-r^{t-1}\left(n\right)|$ [formula five]

G the mean error value that obtains asked on average obtain:

$M\left(i\right)=\frac{1}{G}\underset{t=i+1}{\overset{i+G}{\mathrm{\&Sigma;}}}\mathrm{\&sigma;}\left(t\right)$ [formula six]

At last, in predefined window, obtain the starting point that the minimum pairing value i of M (i) is the OFDM symbol.

In the device shown in Figure 2, discrete Fourier transformer is finished the computing that comprises in [formula one] and [formula three], phase compensation device is finished the computing of [formula three], substracting unit and ask die device to finish the calculating of [formula five], adder is finished the calculating of [formula six], and the minimum value searcher is finished the search of minimum value and determining of starting point in the window.

The above only is a preferred implementation of the present invention; be noted that for those skilled in the art; under the prerequisite that does not break away from the principle of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (2)

1. blind time synchronization method based on loop structure, it is characterized in that: this method comprises the steps:

1) respectively with the i of received signal, i+1 ..., i+G sampled point is that starting point is carried out the discrete Fourier transform (DFT) that N is ordered, the frequency-region signal that to obtain G+1 length be N;

2) each subcarrier to each frequency-region signal carries out the respective phase compensation by side-play amount and subcarrier sequence number;

3) frequency-region signal after the compensation is done N the inverse discrete fourier transform of putting, obtain G+1 time domain sequences;

4) calculate the mean error of former and later two continuous time domain sequences, obtain G mean error value;

5) mean value of G mean error value of calculating is designated as M (i);

6) the pairing i of M (i) of minimum in the watch window, i is the sync bit of OFDM symbol;

Wherein, i is any one sampling location of received signal in the observation window; N is the sub-carrier number of ofdm system; G is the length of Cyclic Prefix.

2. the blind time synchronization method based on loop structure according to claim 1 is characterized in that: G is greater than the maximum delay expansion of wireless multipath fading channel.

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