CN102123125A - Method for realizing fine timing synchronization estimation of OFDM (Orthogonal Frequency Division Multiplexing) system - Google Patents

Abstract

The invention provides a method for realizing fine timing synchronization estimation of an OFDM (Orthogonal Frequency Division Multiplexing) system. The method comprises the following steps of: seeking for an approximate position of a time domain training sequence in a received signal by using a maximum correlation algorithm and taking the time domain training sequence out; setting an extraction interval and extracting the time domain training sequence of the received signal according to the interval; extracting a local training sequence according to the set interval; transforming the time domain training sequence which is subjected to time extraction into a frequency domain training sequence through FFT (Fast Fourier Transform) according to data length after the time extraction; multiplying the frequency domain training sequence by the extracted shift local training sequence and transforming the frequency domain multiplication result back to a time domain through IFFT (Inverse Fast Fourier Transform); and seeking for each peak value for different shift values, wherein the time position corresponding to the maximum peak value is an estimated fine synchronization numerical value. By adopting the technical solution provided by the invention, large frequency deviation can be confronted and quick and accurate fine timing synchronization estimation can be realized; and meanwhile, operation and hardware realization complexity in a fine synchronization estimation algorithm can be effectively reduced.

Description

The smart implementation method of regularly estimating synchronously of a kind of ofdm system

Technical field

The OFDM time synchronized that the present invention relates to the communications field is estimated implementation method, relates in particular to the smart implementation method of regularly estimating synchronously in a kind of ofdm system.

Background technology

The time synchronized of OFDM (being called for short " OFDM ") system is used for providing the position of windowing accurately for fast Fourier transform (being called for short " FFT ") demodulation.Owing between the OFDM symbol, inserted Cyclic Prefix protection at interval, thus the initial moment of OFDM timing synchronization can in protection at interval, change, and can not cause intersymbol interference (being called for short " ISI ") and interchannel interference (abbreviation " ICI ").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 loose relatively to the requirement of timing synchronization.

In many applied environments,, need to determine best symbol regularly in order to obtain best systematic function.Although symbol starting point regularly can be selected arbitrarily in protection at interval; but any symbol variation regularly; the capital increases the sensitivity of ofdm system to the time delay expansion; therefore the patient time delay expansion of institute of system will be lower than its design load; in order to reduce this negative influence as far as possible, need reduce the error of timing synchronization as far as possible.

OFDM regularly is subject to the influence of frequency departure synchronously, and the OFDM technology has been used the orthogonal property of frequency, in case its orthogonality goes to pot, the error rate of system sharply increases, and this is a subject matter of OFDM technology.The main cause that produces frequency deviation is that radio circuit receives and the delivery section centre frequency does not match.If the transmitting terminal centre carrier frequency is f _t, the receiving terminal centre carrier frequency is f _r, then source data x (n) at transmitting terminal is:

At receiving terminal be There is frequency deviation f in the data of receiving terminal after down-conversion as can be seen _r-f _tCan see that from following formula in time domain, the phase deviation that carrier wave frequency deviation caused is along with the increase of sampled point accumulates gradually, equivalence is the linear phase skew.

At frequency domain, disturb between average phase rotation that carrier wave frequency deviation causes and subcarrier, when frequency deviation was Δ f, frequency-region signal can be expressed as:

$Y\left(k\right)=X_k{H}_k\left\{\frac{\sin \mathrm{\π\Δf}}{N\sin (\mathrm{\π\Δf}/N)}\right\}{e}^{\mathrm{j\π\Δf}(N-1)/N}$

$+\underset{\underset{l\≠k}{l=-K}}{\overset{K}{\mathrm{\Σ}}}{X}_k{H}_k\left\{\frac{\sin \mathrm{\π\Δf}}{N\sin (\mathrm{\π}(l-k+\mathrm{\Δf})/N)}\right\}{e}^{\mathrm{j\π\Δf}(N-1)/N}{e}^{-\mathrm{j\π}(l-k)/N}$

Wherein, the signal that Y (k) receives for frequency domain, X _kBe the primary signal that sends, H _kBe the frequency domain response of k position of channel, N is a FFT length, and Y ' (k) and X _kLinear, Y _ICI(k) disturb between subcarrier.Along with the increase of carrier wave frequency deviation Δ f, function

Along with increase, disturb also along with increase between subcarrier.

In ofdm system, when carrier frequency offset takes place, partly be called integer frequency bias Δ f greater than the frequency deviation of subcarrier spacing _I, partly be called decimal frequency bias Δ f less than the frequency deviation of subcarrier spacing _fDecimal frequency bias Δ f wherein _fOrthogonality between each subcarrier of meeting heavy damage.

According to regularly synchronous precision classification, regularly synchronized algorithm can be divided into thick timing synchronized algorithm and smart regularly synchronized algorithm.Usually it is less relatively that thick regularly synchronized algorithm is influenced by frequency deviation, but synchronization accuracy is lower.Smart regularly synchronized algorithm can reach very high synchronization accuracy height, and still along with the increase of frequency deviation, synchronization accuracy sharply reduces.

Summary of the invention

The object of the invention provides a kind of ofdm system the smart implementation method of regularly estimating synchronously, can resist bigger frequency departure, and realization is smart fast and accurately regularly to be estimated synchronously, and the while can be reduced operand and the hardware implementation complexity in the smart algorithm for estimating synchronously.

The smart implementation method of regularly estimating synchronously of a kind of ofdm system comprises following content:

(1) adopts the maximal correlation algorithm to seek the rough position of time-domain training sequence in the received signal, and take out time-domain training sequence;

(2) set one and extract at interval, extract by this interval time-domain training sequence to received signal;

(3) according to the interval of setting, local training sequence is extracted;

(4) according to the data length behind the decimation in time, the time-domain training sequence after the FFT conversion is with decimation in time is transformed to frequency domain training sequence;

(5) the displacement this locality training sequence with frequency domain training sequence and after extracting multiplies each other, and returns time domain by the IFFT operation transform;

(6) seek peak value separately for different shift values, peak-peak time corresponding position is estimated smart numerical value synchronously.

The smart regularly synchronous implementation method of estimating of a kind of ofdm system provided by the present invention all extracts receiving sequence and local sequence, has shortened the data length of the conversion of FFT (fast Fourier transform) and IFFT (inverse fast Fourier transform).Both reduce the complexity of the two realization, reduced the transform operation amount again.Technical solution provided by the present invention can be resisted bigger frequency departure, realizes smart fast and accurately regularly estimation synchronously, effectively reduces operand and hardware implementation complexity in the smart algorithm for estimating synchronously simultaneously.

Description of drawings

The smart implementation method basic flow sheet of regularly estimating synchronously of a kind of ofdm system of Fig. 1

Specific embodiments

Below in conjunction with accompanying drawing, summary of the invention provided by the present invention is described in detail:

(1) time domain receives and is expressed as r (k), adopts maximal correlation (MC) algorithm to seek the rough position of time-domain training sequence in the received signal:

$d_{\mathrm{ML}}=\underset{m}{\arg \max }\left(\right|\{\underset{k=m}{\overset{m+N-1}{\mathrm{\Σ}}}r\left(k\right)\·r^{*}(k+N)\}|$

Wherein, N is the length of time-domain training sequence.

According to the d that calculates _MLTime-domain training sequence r is taken out in the position _C(k).

(2) according to the interval S of a setting, to time-domain training sequence r _C(k) extract.Time-domain training sequence after the extraction is:

r _S(n)＝r _C(S*n)，n＝0，1，2...，N/S

(3) according to setting S at interval, local training sequence is extracted.If local training sequence is expressed as sync (k), k=0,1 ..., N, the local training sequence after then extracting is:

sync _S(n)＝sync(S*n)，n＝0，1，2...，N/S

(4),, the time-domain training sequence behind the decimation in time is transformed to frequency domain training sequence through the FFT conversion according to the data length behind the decimation in time.

R _S(n)＝FFT(r _S(n))n＝0，1，2...，N/S

(5) the displacement this locality training sequence with frequency domain training sequence and after extracting multiplies each other, and obtains the frequency domain multiplied result, and returns time domain by the IFFT operation transform

prod＝IFFT(R _S(n)*sync _S(n-shift))n＝0，1，2...，N／S

(6), seek peak value separately for different shift values.Peak-peak time corresponding position is estimated smart synchronized result.

Claims (1)

1. the smart implementation method of regularly estimating synchronously of an ofdm system is characterized in that comprising following content:

(1) adopts the maximal correlation algorithm to seek the rough position of time-domain training sequence in the received signal, and take out time-domain training sequence;

(2) set one and extract at interval, extract by this interval time-domain training sequence to received signal;

(3) according to the interval of setting, local training sequence is extracted;

(4) according to the data length behind the decimation in time, the time-domain training sequence after the FFT conversion is with decimation in time is transformed to frequency domain training sequence;

(5) the displacement this locality training sequence with frequency domain training sequence and after extracting multiplies each other, and returns time domain by the IFFT operation transform;

(6) seek peak value separately for different shift values, peak-peak time corresponding position is estimated smart numerical value synchronously.

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