CN103746954A - Associated synchronization and frequency offset estimation method for OFDM (Orthogonal Frequency Division Multiplexing) system - Google Patents

Abstract

The invention discloses an associated synchronization and frequency offset estimation method for an OFDM (Orthogonal Frequency Division Multiplexing) system. The method comprises the steps of obtaining sampling point data of two continuous OFDM symbols taking an ith sampling point of a received signal as a starting point; carrying out self-correlation operation on a sampling point in a cyclic prefix of the latter OFDM symbol and a sampling point, and solving average values of the obtained G values, wherein the first sampling point is away from the second sampling point for N sampling points at the tail of the same symbol; carrying out self-correlation operation on the sampling point in the cyclic prefix of the latter OFDM symbol and a sampling point in the precious OFDM symbol, and solving average values of the obtained G values, wherein the first sampling point is away from the second sampling point for N sampling points; adding the obtained results together, searching M addition results according to the number of the OFDM symbols, and solving average values to obtain phi (i) and phi (i), wherein i corresponding to the maximum phi (i) in a watch window provides an OFDM symbol synchronous position, and the phase angle of phi (i) corresponding to the synchronous position provides a frequency offset estimation value. The associated synchronization and frequency offset estimation method for the OFDM system is free of multi-path interference and low in computation complexity, and no training sequence is needed.

Description

A kind of combined synchronization for ofdm system and frequency deviation estimating method

Technical field

The present invention relates to the simultaneous techniques field in mobile communication, relate in particular to one and be applied to symbol and the frequency synchronization method of OFDM (OFDM) system.

Background technology

In mobile communication system, sign synchronization and Nonlinear Transformation in Frequency Offset Estimation are to receive correctly one of the prerequisite of demodulation of data.At present, OFDM become the 4th generation (4G) mobile communication system main flow air interface technologies.4G system adopts respectively DFT-s-OFDM and OFDM technology in up-downgoing.In ofdm system, in order to eliminate intersymbol interference (ISI), to insert a Cyclic Prefix before each OFDM symbol.Copying of Cyclic Prefix is-symbol afterbody, it is greater than the maximum delay expansion of multidiameter fading channel, and the linear convolution of transmitted signal and multipath channel is become to circular convolution simultaneously.In ofdm system, traditional time synchronization method is mainly by training sequence is carried out to auto-correlation computation, and the method for then finding peak value finds the starting point of symbol.This time synchronization method not only needs the training sequence that transmitting and receiving terminal is known, and due to the phase mutual interference that cannot remove between multipath, so that the synchronizing information obtaining all has in multidiameter fading channel is inclined to one side.

Summary of the invention

In order to overcome the deficiencies in the prior art, the invention provides a kind of combined synchronization for ofdm system and frequency deviation estimating method, do not have to disturb between multipath, and computation complexity is low, without any need for training sequence; Fast and reliable of the present invention, estimated accuracy is high, implementation complexity is low, be not only suitable for ofdm system but also be suitable for other having the synchronous estimation method of the mobile communication system of Cyclic Prefix

For achieving the above object, the present invention takes following technical scheme:

For combined synchronization and the frequency deviation estimating method of ofdm system, comprise the steps:

(1) to receive i=0 sampled point of signal in observation window as starting point, extract two continuous OFDM symbol m-1, the sampling number certificate of m, wherein i ∈ Ω, Ω is the number of sampled point in observation window; M=1, m ∈ Γ, Γ is the number that receives OFDM symbol in signal; Suppose that observation window is 100 sampled points, the OFDM symbol of reception has 1,2,3,4,5,6,80 sampled points of each OFDM symbol, first suppose that the 1st sampled point in observation window is OFDM sign-on, first take the 1st sampled point in observation window as starting point, take out 160 sampled datas, be equivalent to two OFDM symbols, corresponding to OFDM symbol 1 and 2, carry out operation below.And then ensuing OFDM symbol 3 and 4 is operated, be finally OFDM symbol 5 and 6.Suppose that again the 2nd sampled point in observation window is OFDM sign-on, aforesaid operations circulates one time.

(2) number of establishing m OFDM symbol cyclic prefix sampled point is G, the sub-carrier number of ofdm system is N, successively the sampled point in m OFDM symbol cyclic prefix and its are carried out to autocorrelation operation at a distance of N sampled point and the sampled point that is positioned at m OFDM symbol afterbody, then the G an obtaining autocorrelation value is averaging;

(3) will in the sampled point in m OFDM symbol cyclic prefix and m-1 OFDM symbol, carry out autocorrelation operation with its sampled point at a distance of N sampled point, and the G an obtaining autocorrelation value is averaging;

(4) by the results added obtaining in step (2) and step (3);

(5) m=m+2, repeating step (1) is to step (4), and to the institute obtaining in steps (4) described addition result be averaging, thereby obtain unbiased estimator φ (i) to channel autocorroelation function and the unbiased estimator of carrier wave frequency deviation

(6) i=i+1, performs step (1) to step (5) successively to receiving the each sampled point of signal in observation window, and in watch window, the maximum corresponding i of φ (i) is the sync bit of OFDM symbol, and this sync bit is corresponding the phase angle estimated value that is carrier wave frequency deviation.

Beneficial effect: (1) the present invention, by introducing the associative operation between two continuous OFDM symbols, has thoroughly got rid of the phase mutual interference between channel multi-path, has obtained without inclined to one side synchronizing information and frequency deviation estimated value; (2) this method does not need to utilize pilot signal or the training sequence that any receiving terminal is known, to system, does not increase any overhead; (3) the present invention proposes combined synchronization and frequency deviation estimating method can be used for the various mobile communication system with Cyclic Prefix including OFDM.

Accompanying drawing explanation

Fig. 1 is workflow diagram of the present invention.

Fig. 2 is the transpose configuration schematic diagram of realizing the inventive method.

Embodiment

Below in conjunction with accompanying drawing, the present invention is further described.

As shown in Figure 1, a kind of combined synchronization for ofdm system provided by the invention and frequency deviation estimating method, comprise the steps:

(1), to receive i=0 sampled point of signal in observation window as starting point, extract two continuous OFDM symbol m-1, the sampling number certificate of m; Wherein i ∈ Ω, Ω is the number of sampled point in observation window; M=1, m ∈ Γ, Γ is the number that receives OFDM symbol in signal;

(2) number of establishing m OFDM symbol cyclic prefix sampled point is G, the sub-carrier number of ofdm system is N, successively the sampled point in m OFDM symbol cyclic prefix and its are carried out to autocorrelation operation at a distance of N sampled point and the sampled point that is positioned at m OFDM symbol afterbody, then the G an obtaining autocorrelation value is averaging;

(3) will in the sampled point in m OFDM symbol cyclic prefix and m-1 OFDM symbol, carry out autocorrelation operation with its sampled point at a distance of N sampled point, and the G an obtaining autocorrelation value is averaging;

(4) by the results added obtaining in step (2) and step (3);

(5) m=m+2, repeating step (1) is to step (4), and to the institute obtaining in steps (4) described addition result be averaging, thereby obtain unbiased estimator φ (i) to channel autocorroelation function and the unbiased estimator of carrier wave frequency deviation

(6) i=i+1, performs step (1) to step (5) successively to receiving the each sampled point of signal in observation window, and in watch window, the maximum corresponding i of φ (i) is the sync bit of OFDM symbol, and sync bit is corresponding the phase angle estimated value that is carrier wave frequency deviation.

Suppose that an ofdm system comprises N subcarrier, the bandwidth of each subcarrier is B, and the length of Cyclic Prefix is G.An OFDM symbol comprises N+G sampled point, and label is from 0 to N+G-1.The sampling period of each sampled point is T, and T=1/NB.Take the sampling number certificate of i sampled point continuous two OFDM symbols as starting point obtains in observation window.First the sampled point in a rear OFDM symbol cyclic prefix and its are carried out to autocorrelation operation at same symbol afterbody at a distance of the sampled point of N sampled point, by carrying out autocorrelation operation with its sampled point at a distance of N sampled point in the sampled point in a rear OFDM symbol cyclic prefix and previous OFDM symbol, then these two results added are obtained to mean value again.Finally, by maximum value search device in window, the starting point of estimate symbol and the frequency deviation of carrier wave.

Specific algorithm is described below:

Suppose that m the OFDM symbol receiving can be expressed as:

$\begin{array}{c}{y}_m\left(n\right)=e^{j2\mathrm{\π\ϵ}[(N+G)m+n]/N}\underset{l=0}{\overset{L-1}{\mathrm{\Σ}}}{h}_l^m\left(n\right)x_m{\left((n-G-l-\mathrm{\θ})\right)}_N+v_m\left(n\right)\\ \mathrm{\θ}+G\≤n\≤\mathrm{\θ}+N+G-1\end{array}---\left(1\right)$

In formula, ε represents by the carrier wave frequency deviation after B normalization; θ represents timing offset; L is the multipath number of channel, (()) _nthe circulative shift operation of expression take N as base.ν _m(n) be the white Gaussian noise of additive zero, variance is

represent that l paths, at the channel parameter in n moment, is the Gaussian random variable of zero-mean, variance is

the auto-correlation function of l paths is:

$E\{h_l\left(m\right)\·h_l^{*}(m+n)\}={\mathrm{\σ}}_l^2{J}_0\left(2\mathrm{\π}{f}_d\mathrm{nT}\right)---\left(2\right)$

In formula, J ₀() represents zeroth order Bezier (Bessel) function, f _dfor maximum doppler frequency.

To receive i sampled point of signal as starting point, structure estimator below:

$\begin{array}{c}{\mathrm{\ρ}}_m^i=\frac{1}{G}\underset{n=0}{\overset{G-1}{\mathrm{\Σ}}}{\mathrm{\λ}}_m^i\left(n\right)\\ =\frac{1}{G}\underset{n=0}{\overset{G-1}{\mathrm{\Σ}}}[y_m(n+i)y_m^{*}(n+N+i)+y_m(n+i)y_{m-1}^{*}(n+G+i)]\end{array}---\left(3\right)$

Suppose i=θ, as 0≤n < L-1,

Due to the sampling { x of m-1 symbol _m-1(n) } with the sampling { x of m symbol _m(n) } separate, and channel gross power is 1, we obtain:

$\begin{array}{c}E\{y_m(n+\mathrm{\&theta;})y_m^{*}(n+N+\mathrm{\&theta;})+y_m(n+\mathrm{\&theta;})y_{m-1}^{*}(n+G+\mathrm{\&theta;})\}\\ =e^{-j2\mathrm{\&pi;\&epsiv;}}\underset{i=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\mathrm{\&sigma;}}_l^2{J}_0\left({2\mathrm{\&pi;f}}_d\mathrm{NT}\right)\\ =e^{-j2\mathrm{\&pi;\&epsiv;}}{J}_0\left(2\mathrm{\&pi;}{f}_d\mathrm{NT}\right)\end{array}---\left(5\right)$

As n >=L-1,

$\begin{array}{c}E\{y_m(n+\mathrm{\&theta;})y_m^{*}(n+N+\mathrm{\&theta;})+y_m(n+\mathrm{\&theta;})y_{m-1}^{*}(n+G+\mathrm{\&theta;})\}\\ =e^{-j2\mathrm{\&pi;\&epsiv;}}{J}_0\left({2\mathrm{\&pi;f}}_d\mathrm{NT}\right)\end{array}----\left(6\right)$

So,

$E\left\{{\mathrm{\&rho;}}_m^{\mathrm{\&theta;}}\right\}=e^{-j2\mathrm{\&pi;\&epsiv;}}{J}_0\left({2\mathrm{\&pi;f}}_d\mathrm{NT}\right)$

From formula (7),

be contemplated to be to channel autocorroelation function and carrier wave frequency deviation without inclined to one side estimation.In concrete Project Realization,

expectation can be by average the asking for of M result, wherein the size of M is to calculate according to the number that receives OFDM symbol in signal.Suppose that observation window is 100 sampled points, the OFDM symbol of reception has 1,2,3,4,5,6, first suppose that the 1st sampled point in observation window is OFDM sign-on, first, take the 1st sampled point in observation window as starting point, take out 160 sampled datas, be equivalent to two OFDM symbols, corresponding to OFDM symbol 1 and 2, carry out operation below.And then ensuing OFDM symbol 3 and 4 is operated, be finally OFDM symbol 5 and 6, i.e. M=3, in like manner analogizes, and during odd number, does not consider last OFDM symbol.Thus, we obtain:

$\mathrm{\&phi;}\left(i\right)=\frac{1}{M}\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}\left|{\mathrm{\&rho;}}_m^i\right|---\left(8\right)$

Finally, take the next sampled point in observation window as OFDM sign-on, circulate an aforesaid operations in predefined window, the maximum corresponding sampled point i of φ (i) is the starting point of OFDM symbol.Starting point is corresponding

phase angle be the estimated result of carrier wave frequency deviation.

Fig. 2 is the transpose configuration schematic diagram of realizing the inventive method, multiplier completes the related operation comprising in formula (3), adder completes the add operation comprising in formula (3) and formula (8), and in window, maximum value search device completes determining of peaked search and starting point.

The above is only the preferred embodiment of the present invention; be noted that for those skilled in the art; under the premise without departing from the principles 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 (1)

1. for combined synchronization and the frequency deviation estimating method of ofdm system, it is characterized in that comprising the steps:

(1) to receive i=0 sampled point of signal in observation window as starting point, extract two continuous OFDM symbol m-1, the sampling number certificate of m, wherein i ∈ Ω, Ω is the number of sampled point in observation window; M=1, m ∈ Γ, Γ is the number that receives OFDM symbol in signal;

(2) number of establishing m OFDM symbol cyclic prefix sampled point is G, the sub-carrier number of ofdm system is N, successively the sampled point in m OFDM symbol cyclic prefix and its are carried out to autocorrelation operation at a distance of N sampled point and the sampled point that is positioned at m OFDM symbol afterbody, then the G an obtaining autocorrelation value is averaging;

(3) will in the sampled point in m OFDM symbol cyclic prefix and m-1 OFDM symbol, carry out autocorrelation operation with its sampled point at a distance of N sampled point, and the G an obtaining autocorrelation value is averaging;

(4) by the results added obtaining in step (2) and step (3);

(5) m=m+2, repeating step (1) is to step (4), and to the institute obtaining in steps (4) described addition result be averaging, thereby obtain unbiased estimator φ (i) to channel autocorroelation function and the unbiased estimator of carrier wave frequency deviation

(6) i=i+1, performs step (1) to step (5) successively to receiving the each sampled point of signal in observation window, and in watch window, the maximum corresponding i of φ (i) is the sync bit of OFDM symbol, and this sync bit is corresponding the phase angle estimated value that is carrier wave frequency deviation.

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