CN103259757B - A kind of synchronous new method of Time And Frequency of effective MIMO-OFDM system - Google Patents

Abstract

The present invention is a kind of synchronous new method of Time And Frequency of effective MIMO-OFDM system, it is characterized in that: under radio communication channel, there is a lot of time-frequency synchronization method in the simultaneous techniques field of MIMO-OFDM system, but net synchronization capability is not fine in MIMO-OFDM system.Therefore, the present invention proposes a kind of synchronous new method of Time And Frequency of effective MIMO-OFDM system.This synchronous method is at transmitting terminal, and adopt time quadrature training sequence to be inserted between the OFDM data symbol of each transmitting antenna, the training sequence β factor values of design affects the autocorrelation of sequence, thus the Timing Synchronization performance of influential system; At receiving terminal, time domain carries out time synchronized and decimal frequency bias is estimated, integer frequency bias estimates it is also complete in time domain simultaneously, therefore, decreases the computation complexity of system.Therefore, compared with traditional synchronized algorithm, the algorithm that the present invention proposes has timing in MIMO-OFDM system, and accurately detection probability height and frequency deviation estimate advantage accurately.

Description

A kind of synchronous new method of Time And Frequency of effective MIMO-OFDM system

Technical field

The present invention relates to MIMO-OFDM technical field, particularly a kind of synchronous new method of Time And Frequency of effective MIMO-OFDM system.

Technical background

Along with the fast development of wireless communication technology, the requirement of people to the speed of mobile communication transmission data is more and more higher.Single-input single-output (SISO, Single-Input Single-Output) system is restricted in channel capacity.Multipath component in propagation can be utilized according to MIMO technology, thus reduce intersymbol interference, improve higher space diversity, radio communication channel capacity and the availability of frequency spectrum can also be improved.And OFDM technology to have the availability of frequency spectrum high, frequency selective fading very capable, easily combines with Multiple Access scheme, supports the advantage of multiple business etc. flexibly.In addition ofdm system due to code check low and add Time Guard Interval thus there is extremely strong anti-multipath jamming ability.MIMO technology and OFDM technology combine and can well realize the validity and reliability of system.MIMO-OFDM is integrated with MIMO and OFDM technology advantage, utilizes MIMO technology under the condition not increasing bandwidth, improve capacity and the availability of frequency spectrum of communication system exponentially, improves the validity of system; Utilize OFDM technology frequency-selective channel can be converted to the feature of flat fading channel thus the reliability application of MIMO technology in broadband wireless data transmission can be realized.

Realize MIMO-OFDM system and have several technical difficult point, comprising requiring that in the process of transmission OFDM data message system has higher net synchronization capability.In MIMO-OFDM system, mainly to comprise Timing Synchronization, Frequency Synchronization and sampling clock synchronous for synchronous error.Timing Synchronization is divided into frame synchronization and sign synchronization, and two process one step completes by the present invention, and reduce system-computed amount with this, Timing Synchronization is the original position determining FFT window in MIMO-OFDM signal receiving process, realizes the correct demodulation of information.Timing Synchronization is the reliability ensureing whole system, is the important guarantee carrying out follow-up frequency deviation estimation simultaneously.Therefore, a kind of synchronous new method of Time And Frequency of effective MIMO-OFDM system, extremely important in the MIMO-OFDM system of high rate data transmission.

During the stationary problem of research MIMO-OFDM system, according to the difference of network topology structure, two kinds of different models are usually divided into study, centralized MIMO-OFDM synchronistic model and distributed MIMO-OFDM synchronistic model.The present invention is mainly applied to centralized MIMO-OFDM synchronistic model.Conventional centralized MIMO-OFDM synchronization scenario has two kinds: (1) the first be insert orthogonal training sequence at each receipts transmitting antenna in same position, the method that can be repeated by multiterminal strengthens the ability of training sequence anti-multipath.But the method shortcoming is time domain orthogonal sequence to be easily affected under a multipath fading channel thus to reduce the orthogonality of sequence, therefore, interference between antenna also increases, and the peak value of its sequence auto-correlation function will thicken, and namely causes system synchronization error to increase.See document: Mody.A.N, Stuber.G.L.Synchronization for MIMO-OFDMsystems.Global Telecommunications Conference.2001.GLOBECOM'01.IEEE.Volume:1,25-29Nov.2001Pages:509-513Vol.1.Mody.A.N, Stuber.G.L.Receiver Implementationfor a MIMO-OFDM System.Global Telecommunications Conference.2002.GLOBECOM'02.IEEE.Volume:1.17-21.Nov.2002 Pages:716-720Vol.1 second method is the method for the training sequence adopting time quadrature, is mutually staggered in time by the training sequence that different transmit antennas is inserted.But the shortcoming of this synchronized algorithm is the increase along with antenna number, the bandwidth shared by quadrature training sequence also increases accordingly, thus causes frequency efficiency to decline, and increases the computation complexity of system.See document: T.C.W.Schenk, A.van Zelst.FrequencySynchronization for MIMO-OFDM Wireless LAN Systems.Proc.IEEEVehicular TechnologyConference Fall2003 (VTC Fall2003), Orlando (FL), 6-9October2003, paper05D-03.Allert vanZelst,Tim C.W.Schenk,Implementation of a MIMO OFDM-Based Wireless LAN System,IEEETRANSACTIONS ON SIGNAL PROCESSING,VOL.52,NO.2,pp.483-494FEBRUARY2004。FAN Hui-li,SUN Jing-fang,YANG Ping,LI Ding-shan,A Robust Timing and FrequencySynchronization Algorithm for HF MIMO OFDM Systems.IEEE CONFERENCEPUBLICATIONS.2010.

In order to overcome now methodical deficiency in simultaneous techniques, the present invention proposes a kind of synchronous new method of Time And Frequency of effective MIMO-OFDM system.The method belongs to data assisted class synchronous method, can improve channel capacity and the availability of frequency spectrum of wireless communication system, and improve the validity of system.

Summary of the invention

The object of the invention is the synchronous new method of Time And Frequency proposing a kind of effective MIMO-OFDM system, thus overcomes the deficiency in existing MIMO-OFDM system and simultaneous techniques thereof.This synchronized algorithm can improve channel capacity and the availability of frequency spectrum of wireless communication system, and improves the validity of system; The training sequence simultaneously designed has strong autocorrelation and more weak cross correlation, can with the data cross-correlation of local transmission after, obtain almost without secondary lobe, single, sharp-pointed peak value, make receiving terminal can judge to realize system synchronization fast, accurately by thresholding, thus the correct demodulation of information of transmission can be ensured.

For achieving the above object, the present invention proposes a kind of synchronous new method of Time And Frequency of effective MIMO-OFDM system, the method overcomes the technical deficiency of existing MIMO-OFDM system synchronization, innovative point of the present invention:

(1) new training sequence T (n) proposing of the present invention, the size proposing the β factor within the specific limits, along with the increase of the β factor, can at the autocorrelation strengthening training sequence in varying degrees.

(2) the present invention propose Timing Synchronization and frequency synchronization algorithm, can by inserting between training sequence to the OFDM data symbol transmitted, according to the cross correlation between training sequence and data symbol, the target function of Timing Synchronization is made to have secondary lobe few, single, sharp-pointed peak value, make receiving terminal can by arranging specific thresholding thus the initial position of Timing Synchronization can being judged fast, accurately, realizing on timing synchronous foundation, carry out Frequency Synchronization, thus ensure the correct demodulation of the data message of transmission.

The synchronous new method of Time And Frequency of a kind of effective MIMO-OFDM system that the present invention proposes realizes its process with dual-mode antenna Nt × Nr, Nt and Nr is positive integer, has:

Step 1: construct new training sequence T (n), along with the increase of β value in training sequence, its sequence self correlation strengthens, and its sequence T (n), has:

$T\left(n\right)\exp \left(\frac{2\mathrm{j\πr}{n}^2}{\mathrm{\βN}}\right),n=\mathrm{0,1},...,N/2-1---\left(1\right)$

Wherein, get r=N/2-1, gcd (r, N/2)=1, β ∈ (1,25);

Step 2: get T (n) sequence and repeat once to construct the training sequence C that length is N ₁n (), has:

$C_1\left(n\right)=\left\{\begin{array}{cc}T\left(n\right)& n\∈\[0,N/2-1\]\\ T(n-N/2)& n\∈\[N/2,N-1\]\end{array}---\left(2\right)\right.$

Step 3: get T (n) sequence and carry out antisymmetry, generates a new sequence T ' (n), has:

$T\left(n\right)=-T(N/2-n),n\∈\[0,N/2-1\]---\left(3\right)$

Step 4: sequence T (n) and T ' (n) is formed the sequence C that length is N ₂n (), has:

$C_2\left(n\right)=\left\{\begin{array}{cc}T\left(n\right)& n\∈\[0,N/2-1\]\\ T^{\′}(n-N/2)& n\∈\[N/2,N-1\]\end{array}---\left(4\right)\right.$

Step 5: at receiving terminal, with local training sequence C ₁n () and Received signal strength carry out cross-correlation, obtain Timing Synchronization, synchronous timing measurements function can be expressed as:

$P\left(d\right)=\underset{i=1}{\overset{\mathrm{Nt}}{\mathrm{\Σ}}}\underset{j=1}{\overset{\mathrm{Nr}}{\mathrm{\Σ}}}\left[\underset{n=0}{\overset{N/2-1}{\mathrm{\Σ}}}{r}_j^{*}(d+n)C_{1,i}\left(n\right)\right]\·{\left[\underset{n=0}{\overset{N/2-1}{\mathrm{\Σ}}}{r}_j^{*}(d+n+N/2)C_{1,i}\left(n\right)\right]}^{*}---\left(5\right)$

$R\left(d\right)=\underset{i=1}{\overset{\mathrm{Nt}}{\mathrm{\Σ}}}\underset{j=1}{\overset{\mathrm{Nr}}{\mathrm{\Σ}}}\underset{n=1}{\overset{N/2-1}{\mathrm{\Σ}}}\left|C_{1,i}^{*}(n+d)C_{1,i}(n+d)\right|---\left(6\right)$

$M\left(d\right)=\frac{\left|P^2\left(d\right)\right|}{R^2\left(d\right)}---\left(7\right)$

Wherein, Nt is transmitting terminal sky number of lines, Nr is receiving terminal sky number of lines, N is the length not comprising Cyclic Prefix OFDM symbol, d is integer value, and d represents the relative sliding position of the sequence of reception relative to local sequence, and n is the sampling number of Received signal strength, () * represents that the data in bracket get conjugate operation, C _{1, i}(.) represents first training sequence that each transmitting antenna inserts, represent that the data-signal that each reception antenna transmits gets conjugate operation;

Step 6: by setting simple threshold value, target function M (d) is exceeded position that threshold value d value is judged to Timing Synchronization, i.e. synchronization point:

${\mathrm{\τ}}_{\mathrm{estl}}=\arg \underset{d}{\max }\left(M\left(d\right)\right)---\left(8\right)$

Step 7: carry out decimal frequency bias estimated value:

${\mathrm{\ϵ}}_f=\frac{1}{\mathrm{\π}}\mathrm{angle}\left(R\left({\mathrm{\τ}}_{\mathrm{estl}}\right)\right)---\left(9\right)$

In formula $R\left({\mathrm{\τ}}_{\mathrm{estl}}\right)=\underset{j=0}{\overset{\mathrm{Nr}}{\mathrm{\Σ}}}\underset{n=0}{\overset{N/2-1}{\mathrm{\Σ}}}{r}_j^{*}({\mathrm{\τ}}_{\mathrm{estl}}+n)({\mathrm{\τ}}_{\mathrm{estl}}+n+N/2)---\left(10\right)$

Wherein, decimal frequency bias estimation range ε _f∈ (0,1);

Step 8: carry out integer frequency bias estimation by after the fractional frequency migration estimated, it is direct estimation ε under the condition of time domain that integer frequency bias is estimated _i, eliminate FFT computing, integer frequency bias estimated value:

${\mathrm{\ϵ}}_i={\mathrm{\τ}}_{\mathrm{est}2}-{\mathrm{\τ}}_{\mathrm{esstl}}-N-\mathrm{Ng}+1---\left(11\right)$

$Q\left(d^{\′}\right)=\underset{i=1}{\overset{\mathrm{Nt}}{\mathrm{\Σ}}}\underset{j=1}{\overset{\mathrm{Nr}}{\mathrm{\Σ}}}\left[\underset{n=0}{\overset{N/2-1}{\mathrm{\Σ}}}{r}_j^{*}(d^{\′}+n)C_{2,i}\left(n\right)\right]\·{\left[\underset{n=0}{\overset{N/2-1}{\mathrm{\Σ}}}{r}_j^{*}(d^{\′}+N/2-n)C_{2,.i}\left(n\right)\right]}^{*}---\left(12\right)$

${\mathrm{\τ}}_{\mathrm{esst}2}=\arg \underset{d^{\′}}{\max }\left(Q\left(d^{\′}\right)\right)---\left(13\right)$

Wherein, Ng represents the length of Cyclic Prefix, C _{2, i}() represents second training sequence that each transmitting antenna inserts, represent that the data-signal that each reception antenna transmits gets conjugate operation, the search in formula (12) and (13) is with d '=τ _est1centered by+N+Ng, integer frequency bias estimation range ε _i∈ (-N/4, N/4).

Accompanying drawing explanation

In order to a kind of synchronous new method of Time And Frequency of effective MIMO-OFDM system is clearly described, simply introduce for involved accompanying drawing of the present invention.

Fig. 1 is the MIMO-OFDM system fundamental block diagram that the present invention has Nt transmit antennas and Nr root reception antenna;

In figure, MIMO-OFDM system block diagram is mainly made up of transmitting terminal and receiving terminal.Mainly comprise at transmitting terminal: coding 2, MIMO coding 4, FFT modulation 6; Mainly comprise at receiving terminal: Timing Synchronization and Frequency Synchronization 9, FFT demodulation 11, channel estimating 13, MIMO decodes 14, decoding 16, the stay of two nights 17.

Fig. 2 is that the present invention inserts training sequence basic structure block diagram;

In figure, training sequence is inserted between each transmitting antenna OFDM data symbol with the form of time quadrature.

Fig. 3 is training sequence structure method schematic diagram of the present invention;

In figure, C ₁n () is that to get that T (n) sequence repeats once to construct length be N training sequence, C ₂n sequence T (n) and T ' (n) is formed length by () is N training sequence.

Fig. 4 is the method schematic diagram of Timing Synchronization of the present invention and Frequency Synchronization;

In figure, carry out cross-correlation between training sequence and the data message of local transmission, setting threshold value, determines the original position of FFT window, after determining sync bit, then carries out frequency deviation estimation.

Fig. 5 is the performance simulation figure of β=10 of the present invention timing synchronization algorithm correct probability;

In figure, abscissa represents signal to noise ratio (SNR), and ordinate represents synchronous correct probability, and β represents the synchronous correct probability factor of impact.Can find out in figure that traditional algorithm and innovatory algorithm are under the identical β factor, the synchronous correct probability of innovatory algorithm will be far superior to traditional algorithm.

Fig. 6 is the performance simulation figure that decimal frequency bias of the present invention estimates mean square error (MSE);

In figure, abscissa represents signal to noise ratio (SNR), and ordinate represents that decimal frequency bias estimates mean square error (MSE), and β represents the synchronous correct probability factor of impact.Can find out in figure that traditional algorithm and innovatory algorithm are under the identical β factor, the frequency deviation of innovatory algorithm estimates that mean square error (MSE) wants performance to be better than traditional algorithm.

Fig. 7 is that frequency deviation of the present invention estimates mean square error (MSE) performance simulation figure;

In figure, abscissa represents signal to noise ratio (SNR), and ordinate represents that frequency deviation estimates mean square error (MSE), and β represents the synchronous correct probability factor of impact.

Fig. 8 is the performance simulation figure of the timing synchronization algorithm correct probability that the β factor of the present invention is different;

In figure, abscissa represents signal to noise ratio (SNR), and ordinate represents synchronous correct probability, and β represents the synchronous correct probability factor of impact.

Can find out in figure, under identical signal to noise ratio, the β factor is larger, and the synchronous correct probability of system is higher.

Embodiment

Below in conjunction with embodiment, the synchronous new method of Time And Frequency that the present invention is a kind of effective MIMO-OFDM system is described in further detail.

Fig. 1 is the MIMO-OFDM system fundamental block diagram that the present invention has Nt transmit antennas and Nr root reception antenna.A kind of synchronous new method of Time And Frequency of effective MIMO-OFDM system is primarily of transmitting terminal and receiving terminal composition.At transmitting terminal, mainly include data source modules 1, coding module 2, sign map module 3, MIMO coding module, insertion pilot module 5, the IFFT module 6 on each transmitting antenna, inserts training sequence module 7, inserts protection interval module 8.Timing Synchronization and frequency synchronization module 9 is mainly included, removal protection interval module 10, the FFT module 11 on each reception antenna at receiving terminal; extract pilot module 12, and channel estimation module 13, MIMO decoder module 14; separate sign map module 15, decoder module 16, stay of two nights module 17.In the training sequence module 7 of the insertion of receiving terminal, this training sequence module produces two training sequences isometric with OFDM data symbol.Also need before this through MIMO coding module 4, namely this module is the multiplexing or space diversity precoding technique in application space, and the present invention mainly adopts spatial reuse and coding techniques.Obtain at receiving terminal the original position that Timing Synchronization and frequency synchronization module 9 mainly determine FFT window, ensure that OFDM data symbol can correctly demodulation, mutual orthogonality between each subcarrier of Frequency Synchronization principal security; Channel estimation module 13 mainly utilizes training sequence to estimate multipath channel time-domain response; Carry out the demodulation that MIMO decoder module 14 and decoder module 16 realize OFDM data symbol subsequently.Fig. 2 is that the present invention inserts training sequence basic structure block diagram, training sequence is inserted between OFDM symbol with the form of time quadrature, but due to be multiple-input and multiple-output MIMO-OFDM system in, training sequence is inserted between each transmitting antenna OFDM data symbol with the form of time quadrature.

Fig. 3 is training sequence structure method schematic diagram of the present invention, and for MIMO-OFDM synchro system, want receiving terminal accurately by data demodulates out, Timing Synchronization is particularly important.And the training sequence constructing good autocorrelation and weak cross correlation ensures the important prerequisite of OFDM symbol at receiving terminal Timing Synchronization.The method of the training sequence structure of good autocorrelation: training sequence T (n) that 301 structures one are new, along with the increase of β value in training sequence, its sequence self correlation strengthens; 302 get T (n) sequence repeats once to construct the training sequence C that length is N ₁(n); 303 get T (n) sequence carries out antisymmetry, generates a new sequence T ' (n); Sequence T (n) and T ' (n) is formed the sequence C that length is N by 304 ₂(n).

Citing: get N=32, during β=10, training sequence C ₁(n) actual sequence

Get N=32, during β=10, training sequence C ₂the actual sequence of (n).

Fig. 4 is the method schematic diagram of Timing Synchronization of the present invention and Frequency Synchronization, and 401 is Received signal strength; 402 is local training sequence C of receiving terminal ₁n () and Received signal strength carry out cross-correlation, obtain Timing Synchronization, synchronous timing measurements function can be expressed as:

$P\left(d\right)=\underset{i=1}{\overset{\mathrm{Nt}}{\mathrm{\Σ}}}\underset{j=1}{\overset{\mathrm{Nr}}{\mathrm{\Σ}}}\left[\underset{n=0}{\overset{n/2-1}{\mathrm{\Σ}}}{r}_j^{*}(d+n)C_{1,i}\left(n\right)\right]\·{\left[\underset{n=0}{\overset{N/2-1}{\mathrm{\Σ}}}{r}_j^{*}(d+n+N/2)C_{1,i}\left(n\right)\right]}^{*}---\left(6\right)$

$R\left(d\right)=\underset{i=1}{\overset{\mathrm{Nt}}{\mathrm{\Σ}}}\underset{j=1}{\overset{\mathrm{Nr}}{\mathrm{\Σ}}}\underset{n=1}{\overset{N/2-1}{\mathrm{\Σ}}}|C_{1,i}^{*}(n+d)\·C_{1,i}(n+d)|---\left(7\right)$

$M\left(d\right)=\frac{\left|P^2\left(d\right)\right|}{R^2\left(d\right)}---\left(8\right)$

403 is setting threshold values, when target function M (d) exceedes the position that threshold value d value is judged to Timing Synchronization:

${\mathrm{\τ}}_{\mathrm{estl}}=\arg \underset{d}{\max }\left(M\left(d\right)\right)---\left(9\right)$

404 is determine sync bit, carries out frequency deviation estimation, and the target function that frequency deviation is estimated is expressed as:

Carry out decimal frequency bias estimated value:

${\mathrm{\ϵ}}_f=\frac{1}{\mathrm{\π}}\mathrm{angle}\left(R\left({\mathrm{\τ}}_{\mathrm{estl}}\right)\right)---\left(10\right)$

In formula $R\left({\mathrm{\τ}}_{\mathrm{estl}}\right)=\underset{j=0}{\overset{\mathrm{Nr}}{\mathrm{\Σ}}}\underset{n=0}{\overset{N/2-1}{\mathrm{\Σ}}}{r}_j^{*}({\mathrm{\τ}}_{\mathrm{estl}}+n)r_j({\mathrm{\τ}}_{\mathrm{estl}}+n+N/2)---\left(11\right)$

Wherein, decimal frequency bias estimation range is ε _f∈ (0,1).

405 is estimated by the integer frequency bias of the laggard line frequency of fractional frequency migration estimated, and 406 is that integer frequency bias that the present invention proposes estimates it is the ε of direct estimation under the condition of time domain _i, thus eliminate FFT computing.Integer frequency bias estimated value:

${\mathrm{\ϵ}}_i={\mathrm{\τ}}_{\mathrm{est}2}-{\mathrm{\τ}}_{\mathrm{est}1}-N-\mathrm{Ng}+1---\left(12\right)$

$Q\left(d^{\′}\right)=\underset{i=1}{\overset{\mathrm{Nt}}{\mathrm{\Σ}}}\underset{j=1}{\overset{\mathrm{Nr}}{\mathrm{\Σ}}}\left[\underset{n=0}{\overset{N/2-1}{\mathrm{\Σ}}}{r}_j^{*}(d^{\′}+n)C_{2,i}\left(n\right)\right]\·{\left[\underset{n=0}{\overset{N/2-1}{\mathrm{\Σ}}}{r}_j^{*}(d^{\′}+N/2-n)C_{2,i}\left(n\right)\right]}^{*}---\left(13\right)$

${\mathrm{\τ}}_{\mathrm{esst}2}=\arg \underset{d^{\′}}{\max }\left(Q\left(d^{\′}\right)\right)---\left(14\right)$

Wherein, Ng represents the length of Cyclic Prefix, C _{2, i}(.) represents second training sequence inserted on each transmitting antenna, r _j(.) represents the data-signal that each reception antenna transmits, and the search in formula (13) and (14) is with d '=τ _est1centered by+N+Ng.The scope ε that integer frequency bias is estimated _i∈ (-N/4, N/4).

Fig. 5 is the performance simulation figure of β=10 of the present invention timing synchronization algorithm correct probability.The major parameter of simulation process of the present invention is arranged: simulation times 10000 times, transmitting terminal antenna number is 2, modulation system is BPSK, sub-carrier number N=1024, circulating prefix-length is N/4, under channel circumstance is chosen at multidiameter fading channel environment, choose the training sequence of β=10 as traditional algorithm and the synchronous correct probability Performance comparision of algorithm of the present invention.Traditional algorithm is: Allert van Zelst, Tim C.W.Schenk, Implementation of aMIMO OFDM-Based Wireless LAN System, IEEE TRANSACTIONS ON SIGNAL PROCESSING, VOL.52, NO.2, pp.483-494, FEBRUARY2004.As can be seen from analogous diagram, the synchronous correct probability of its traditional algorithm reaches 90% signal to noise ratio and is about 0dB, and when synchronous correct probability of the present invention reaches 90%, signal to noise ratio is about-18dB.Therefore, the timing synchronization algorithm performance that the present invention proposes is far superior to traditional algorithm.

Fig. 6 is that decimal frequency bias of the present invention estimates mean square error analogous diagram.The major parameter of simulation process of the present invention is arranged: simulation times 10000 times, transmitting terminal antenna number is 2, and modulation system is BPSK, sub-carrier number N=1024, and circulating prefix-length is N/4, under channel circumstance is chosen at multidiameter fading channel environment, gets frequency shift (FS) ε _f=0.3, choose the training sequence of β=10 as traditional algorithm and algorithm of the present invention synchronous decimal frequency bias algorithm for estimating Performance comparision.As can be seen from the figure, traditional algorithm decimal frequency bias estimates that mean square error is 10 ^-3time, signal to noise ratio is about 0dB, and the algorithm decimal frequency bias that the present invention proposes estimates that mean square error is 10 ^-3time, signal to noise ratio is about-10dB.Therefore, the Frequency Synchronization performance that the present invention proposes is better than traditional algorithm.

Fig. 7 is that frequency deviation of the present invention estimates mean square error (MSE) performance simulation figure.The major parameter of simulation process of the present invention is arranged: simulation times 10000 times, transmitting terminal antenna number is 2, modulation system is BPSK, sub-carrier number N=1024, circulating prefix-length is N/4, under channel circumstance is chosen at multidiameter fading channel environment, gets frequency shift (FS) ε=50.3, as can be seen from analogous diagram, the frequency deviation that the present invention proposes estimates that mean square error is 10 ^-3time, signal to noise ratio is about-6dB.

Fig. 8 is the performance simulation figure of the timing synchronization algorithm correct probability that the β factor of the present invention is different.The major parameter of simulation process of the present invention is arranged: simulation times 10000 times, and transmitting terminal antenna number is 2, and modulation system is BPSK, sub-carrier number N=1024, and circulating prefix-length is N/4, and channel circumstance is chosen at multidiameter fading channel environmental frequencies skew ε _f=0.3, choose the β factor and increase gradually, the synchronous correct probability performance of its system also strengthens.Under identical signal to noise ratio condition during-20dB, β=1, synchronous correct probability is 60%, β=5, and synchronous correct probability is 70%, β=10, and synchronous correct probability is 80%.Therefore, the value of the β factor is different, on system synchronization performance also impact to some extent.

Claims (2)

1. the synchronous new method of Time And Frequency of effective MIMO-OFDM system, this method is mainly used in centralized MIMO-OFDM synchronistic model, and its characteristic value is:

Step 1: construct new training sequence T (n), along with the increase of β value in training sequence, its sequence self correlation strengthens, and its sequence T (n), has:

$\begin{array}{cc}T\left(n\right)=\exp \left(\frac{2{\mathrm{j\πrn}}^2}{\mathrm{\β}N}\right)& n=0,1,\mathrm{...},N/2-1\end{array}---\left(1\right)$

Wherein, get r=N/2-1, gcd (r, N/2)=1, β ∈ (1,25);

Step 2: get T (n) sequence and repeat once to construct the training sequence C that length is N ₁n (), has:

$C_1\left(n\right)=\{\begin{array}{cc}T\left(n\right)& n\∈\[0,N/2-1\]\\ T(n-N/2)& n\∈\[N/2,N-1\]\end{array}---\left(2\right)$

Step 3: get T (n) sequence and carry out antisymmetry, generates a new sequence T ' (n), has:

T′(n)＝-T(N/2-n) n∈[0,N/2-1] (3)

Step 4: sequence T (n) and T ' (n) is formed the sequence C that length is N ₂n (), has:

$C_2\left(n\right)=\{\begin{array}{cc}T\left(n\right)& n\∈\[0,N/2-1\]\\ T^{\′}(n-N/2)& n\∈\[N/2,N-1\]\end{array}---\left(4\right)$

Step 5: at receiving terminal, with local training sequence C ₁n () and Received signal strength carry out cross-correlation, obtain Timing Synchronization, synchronous timing measurements function can be expressed as:

$P\left(d\right)=\underset{i=1}{\overset{Nt}{\Σ}}\underset{j=1}{\overset{Nr}{\Σ}}\[\underset{n=0}{\overset{N/2-1}{\Σ}}{r}_j^{*}(d+n)C_{1,i}\left(n\right)\]\·{\[\underset{n=0}{\overset{N/2-1}{\Σ}}{r}_j^{*}(d+n+N/2)C_{1,i}\left(n\right)\]}^{*}---\left(5\right)$

$R\left(d\right)=\underset{i=1}{\overset{Nt}{\Σ}}\underset{j=1}{\overset{Nr}{\Σ}}\underset{n=1}{\overset{N/2-1}{\Σ}}|C_{1,i}^{*}(n+d)\·C_{1,i}(n+d)|---\left(6\right)$

$M\left(d\right)=\frac{\left|P^2\left(d\right)\right|}{R^2\left(d\right)}---\left(7\right)$

Wherein, Nt is transmitting terminal sky number of lines, Nr is receiving terminal sky number of lines, N is the length not comprising Cyclic Prefix OFDM symbol, d is integer value, and d represents the relative sliding position of the sequence of reception relative to local sequence, and n is the sampling number of Received signal strength, () * represents that the data in bracket get conjugate operation, C _{1, i}() represents first training sequence that each transmitting antenna inserts, represent that the data-signal that each reception antenna transmits gets conjugate operation;

Step 6: by setting simple threshold value, target function M (d) is exceeded position that threshold value d value is judged to Timing Synchronization, i.e. synchronization point:

${\mathrm{\τ}}_{est1}=\underset{d}{\arg max}\left(M\right(d\left)\right)---\left(8\right)$

Step 7: carry out decimal frequency bias estimated value:

${\mathrm{\ϵ}}_f=\frac{1}{\mathrm{\π}}angle\left(R\right({\mathrm{\τ}}_{est1}\left)\right)---\left(9\right)$

In formula $R\left({\mathrm{\τ}}_{est1}\right)=\underset{j=0}{\overset{Nr}{\Σ}}\underset{n=0}{\overset{N/2-1}{\Σ}}{r}_j^{*}({\mathrm{\τ}}_{est1}+n)r_j({\mathrm{\τ}}_{est1}+n+N/2)---\left(10\right)$

Wherein, decimal frequency bias estimation range ε _f∈ (0,1);

Step 8: carry out integer frequency bias estimation by after the fractional frequency migration estimated, it is direct estimation ε under the condition of time domain that integer frequency bias is estimated _i, eliminate FFT computing, integer frequency bias estimated value:

ε _i＝τ _est2-τ _est1-N-Ng+1 (11)

$Q\left(d^{\′}\right)=\underset{i=1}{\overset{Nt}{\Σ}}\underset{j=1}{\overset{Nr}{\Σ}}\[\underset{n=0}{\overset{N/2-1}{\Σ}}{r}_j^{*}(d^{\′}+n)C_{2,i}\left(n\right)\]\·{\[\underset{n=0}{\overset{N/2-1}{\Σ}}{r}_j^{*}(d^{\′}+N/2-n)C_{2,i}\left(n\right)\]}^{*}---\left(12\right)$

${\mathrm{\τ}}_{est2}=\underset{d^{\′}}{\arg max}\left(Q\right(d^{\′}\left)\right)---\left(13\right)$

Wherein, Ng represents the length of Cyclic Prefix, C _{2, i}() represents second training sequence that each transmitting antenna inserts, represent that the data-signal that each reception antenna transmits gets conjugate operation, the search in formula (12) and (13) is with d '=τ _est1centered by+N+Ng, integer frequency bias estimation range ε _i∈ (-N/4, N/4).

2. the synchronous new method of Time And Frequency of a kind of effective MIMO-OFDM system according to claim 1, it is characterized in that: propose new training sequence T (n), according to the difference of the β factor, Timing Synchronization accuracy is with the increase of the β factor, and its timing net synchronization capability strengthens.