CN103259757A - Efficient time and frequency synchronizing novel method of MIMO-OFDM system - Google Patents

Abstract

The invention provides an efficient time and frequency synchronizing novel method of an MIMO-OFDM system. The system is characterized in that a great number of time and frequency synchronizing methods exist in the technical field of synchronization of the MIMO-OFDM system under a wireless communication channel, yet synchronization performances in the MIMO-OFDM system is poor. Therefore, the efficient time and frequency synchronizing novel method of the MIMO-OFDM system is provided. According to the efficient time and frequency synchronizing novel method of the MIMO-OFDM system, at a sending end, time orthogonal training sequences are inserted among the OFDM data symbols of all transmitting antennas, beta factor values of the designed training sequences influence autocorrelation of the sequences, and therefore the timing synchronization performance of the system is influenced; at a receiving end, a time domain carries out time synchronization and fractional part frequency offset estimation, meanwhile, integer frequency offset estimation is also completed in the time domain, and therefore computation complexity of the system is reduced. Therefore, compared with a traditional synchronization algorithm, the algorithm provided by the efficient time and frequency synchronizing novel method of the MIMO-OFDM system has the advantages of being accurate in timing, high in detection probability and accurate in frequency offset estimation in the MIMO-OFDM system.

Description

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

Technical field

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

Technical background

Along with the fast development of wireless communication technology, people are more and more higher to the requirement of the speed of mobile communication transmission data.(SISO, Single-Input Single-Output) system is restricted in channel capacity for the single output of single input.Can utilize multipath component in the propagation according to the MIMO technology, thereby reduce intersymbol interference, improve higher space diversity, can also improve radio communication channel capacity and the availability of frequency spectrum.And the OFDM technology has availability of frequency spectrum height, and frequency selective fading very capable combines with the multiple access scheme easily, supports the advantage of multiple business etc. flexibly.Ofdm system is because code check is low and added guardtime at interval thereby have an extremely strong anti-multipath interference performance in addition.MIMO technology and OFDM technology combine validity and the reliability of the system that can well realize.MIMO-OFDM is integrated MIMO and OFDM technological merit utilizes the MIMO technology to improve capability of communication system and the availability of frequency spectrum exponentially under the condition that does not increase bandwidth, improved the validity of system; Thereby the characteristics of utilizing the OFDM technology frequency-selective channel can be converted to flat fading channel can realize the reliable application of MIMO technology in the broadband wireless transfer of data.

Realize that there are several technical difficult points in the MIMO-OFDM system, comprising in the process of transmission OFDM data message, requiring system that the higher synchronous performance is arranged.Synchronous error mainly comprises regularly synchronously in the MIMO-OFDM system, Frequency Synchronization and sampling clock be synchronous.Regularly be divided into frame synchronization and sign synchronization synchronously, the present invention finishes two one step of process, reduces the system-computed amount with this, regularly is the original position of determining FFT window in the MIMO-OFDM signal demodulating process synchronously, realizes the correct demodulation of information.Being the reliability that guarantees whole system synchronously regularly, is to carry out the important assurance that follow-up frequency deviation is estimated simultaneously.Therefore, the synchronous new method of Time And Frequency of a kind of effective MIMO-OFDM system, extremely important in the MIMO-OFDM of high rate data transmission system.

When studying the stationary problem of MIMO-OFDM system, according to the difference of network topology structure, be divided into two kinds of different models usually and study, centralized MIMO-OFDM synchronistic model and distributed MIMO-OFDM synchronistic model.The present invention is applied to centralized MIMO-OFDM synchronistic model.Common centralized MIMO-OFDM synchronization scenario has two kinds: (1) first kind is to penetrate antenna at the training sequence of same position insertion quadrature in each transmitting-receiving, can strengthen the ability of training sequence anti-multipath by the method that multiterminal repeat.Thereby but this method shortcoming is the time domain orthogonal sequence to be affected easily under multidiameter fading channel and to have weakened the orthogonality of sequence, therefore, interference between antenna has also increased, and the peak value of its sequence auto-correlation function will thicken, and namely causes the system synchronization error to increase.Referring to document: Mody.A.N, Stuber.G.L.Synchronization for MIMO-OFDM systems.Global Telecommunications Conference.2001.GLOBECOM'01.IEEE.Volume:1,25-29Nov.2001Pages:509-513Vol.1.Mody.A.N, Stuber.G.L.Receiver Implementation for a MIMO-OFDM System.Global Telecommunications Conference.2002.GLOBECOM'02.IEEE.Volume:1.17-21.Nov.2002 Pages:716-720Vol.1 second method is to adopt the method for the training sequence of time quadrature, staggers mutually in time by the training sequence that inserts on the different transmit antennas.But the shortcoming of this synchronized algorithm is the increase along with antenna number, and the shared bandwidth of quadrature training sequence also increases accordingly, thereby causes frequency efficiency to descend, and has increased the computation complexity of system.Referring to document: T.C.W.Schenk, A.van Zelst.Frequency Synchronization for MIMO-OFDM Wireless LAN Systems.Proc.IEEEVehicular Technology Conference Fall2003 (VTC Fall2003), Orlando (FL), 6-9October2003, paper05D-03.Allert van Zelst,Tim C.W.Schenk,Implementation of a MIMO OFDM-Based Wireless LAN System,IEEE TRANSACTIONS 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 Frequency Synchronization Algorithm for HF MIMO OFDM Systems.IEEE CONFERENCE PUBLICATIONS.2010.

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

Summary of the invention

The object of the invention is to propose the synchronous new method of Time And Frequency of a kind of effective MIMO-OFDM system, thereby overcomes the deficiency on existing MIMO-OFDM system and the simultaneous techniques thereof.This synchronized algorithm can improve channel capacity and the availability of frequency spectrum of wireless communication system, and has improved the validity of system; She Ji training sequence has strong autocorrelation and more weak cross correlation simultaneously, can with the data cross-correlation of this locality transmission after, obtain almost not have secondary lobe, single, sharp-pointed peak value, receiving terminal can be judged by thresholding realize system synchronization fast, accurately, thereby can guarantee the correct demodulation of information transmitted.

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

(1) a new training sequence T (n) of the present invention's proposition proposes the size of the β factor within the specific limits, along with the increase of the β factor, and can be at the autocorrelation that strengthens training sequence in varying degrees.

(2) the synchronous and frequency synchronization algorithm of the timing of the present invention's proposition, can be by inserting training sequence between the OFDM data symbol of transmission, according to the cross correlation between training sequence and the data symbol, it is few that feasible regularly synchronous target function has secondary lobe, single, sharp-pointed peak value, thereby make receiving terminal can judge regularly synchronous initial position fast, accurately by specific thresholding is set, on realization system timing synchronous foundation, carry out Frequency Synchronization, thereby guarantee 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 is to realize its process with dual-mode antenna Nt * Nr, and Nt and Nr are positive integer, have:

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

$T\left(n\right)\exp \left(\frac{2\mathrm{j\&pi;<figure-callout\; id="2"\; label="r\; n"\; filenames="130522085311.png,130522085332.png"\; state="\{\{state\}\}">r</figure-callout>}{n}^{}{}^2}{\mathrm{\&beta;N}}\right),n=\mathrm{0,1},...,N/2-1---\left(1\right)$

Wherein, get r=N/2-1, and 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 ₁(n), have:

$C_1\left(n\right)=\left\{\begin{array}{cc}T\left(n\right)& n\&Element;\&lsqb;0,N/2-1\&rsqb;\\ T(n-N/2)& n\&Element;\&lsqb;N/2,N-1\&rsqb;\end{array}---\left(2\right)\right.$

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

$T\left(n\right)=-T(N/2-n),n\&Element;\&lsqb;0,N/2-1\&rsqb;---\left(3\right)$

Step 4: sequence T (n) and T ' (n) are constituted the sequence C that length is N ₂(n), have:

$C_2\left(n\right)=\left\{\begin{array}{cc}T\left(n\right)& n\&Element;\&lsqb;0,N/2-1\&rsqb;\\ T^{\&prime;}(n-N/2)& n\&Element;\&lsqb;N/2,N-1\&rsqb;\end{array}---\left(4\right)\right.$

Step 5: at receiving terminal, with local training sequence C ₁(n) carry out cross-correlation with the reception signal, obtain regularly synchronously, synchronous timing is measured function and can be expressed as:

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

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

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

Wherein, Nt is transmitting terminal sky number of lines, Nr is receiving terminal sky number of lines, N is a length that does not comprise Cyclic Prefix OFDM symbol, d is integer value, and d represents the sequence that receives with respect to the relative sliding position of local sequence, and n counts for receiving signals sampling, () * represents that the data in the bracket get conjugate operation, C _{1, i}(.) represents first training sequence of inserting on each transmitting antenna,

Represent that data signals transmitted is got conjugate operation on each reception antenna;

Step 6: by setting simple threshold value, make target function M (d) surpass threshold value d value and be judged to regularly synchronization position, i.e. synchronization point:

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

Step 7: carry out the decimal frequency bias estimated value:

${\mathrm{\&epsiv;}}_f=\frac{1}{\mathrm{\&pi;}}\mathrm{angle}\left(R\left({\mathrm{\&tau;}}_{\mathrm{estl}}\right)\right)---\left(9\right)$

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

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

Step 8: estimate that with carrying out integer frequency bias behind the decimal frequency offset compensation that estimates it is direct estimation ε under the condition of time domain that integer frequency bias is estimated _i, saved the FFT computing, the integer frequency bias estimated value:

${\mathrm{\&epsiv;}}_i={\mathrm{\&tau;}}_{\mathrm{est}2}-{\mathrm{\&tau;}}_{\mathrm{esstl}}-N-\mathrm{Ng}+1---\left(11\right)$

$Q\left(d^{\&prime;}\right)=\underset{i=1}{\overset{\mathrm{Nt}}{\mathrm{\&Sigma;}}}\underset{j=1}{\overset{\mathrm{Nr}}{\mathrm{\&Sigma;}}}\left[\underset{n=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}{r}_j^{*}(d^{\&prime;}+n){\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="130522085311.png,130522085332.png"\; state="\{\{state\}\}">C</figure-callout>}}_{2,i}\left(n\right)\right]\&CenterDot;{\left[\underset{n=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}{r}_j^{*}(d^{\&prime;}+N/2-n){\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="130522085311.png,130522085332.png"\; state="\{\{state\}\}">C</figure-callout>}}_{2,.i}\left(n\right)\right]}^{*}---\left(12\right)$

${\mathrm{\&tau;}}_{\mathrm{<figure-callout\; id="2"\; label="esst"\; filenames="130522085311.png,130522085332.png"\; state="\{\{state\}\}">esst</figure-callout>}2}=\arg \underset{d^{\&prime;}}{\max }\left(Q\left(d^{\&prime;}\right)\right)---\left(13\right)$

Wherein, Ng represents the length of Cyclic Prefix, C _{2, i}() represents second training sequence inserting on each transmitting antenna,

Represent that data signals transmitted is got conjugate operation on each reception antenna, the search in formula (12) and (13) is with d '=τ _Est1Centered by+the N+Ng, integer frequency bias estimation range ε _i∈ (N/4, N/4).

Description of drawings

For the synchronous new method of Time And Frequency of a kind of effective MIMO-OFDM system more clearly is described, simply introduce at related 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;

Among the figure, the MIMO-OFDM system block diagram mainly is 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: the synchronous and Frequency Synchronization 9 of timing, FFT demodulation 11, channel estimating 13, MIMO decoding 14, decoding 16, the stay of two nights 17.

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

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

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

Among the figure, C ₁(n) be to get T (n) sequence to repeat once to construct length be the N training sequence, C ₂(n) sequence T (n) and T ' (n) being constituted length is the N training sequence.

Fig. 4 be the present invention regularly synchronously and the method schematic diagram of Frequency Synchronization;

Among the figure, carry out cross-correlation between the data message of training sequence and local transmission, set threshold value, determine the original position of FFT window, determine sync bit after, carry out frequency deviation again and estimate.

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

Among the figure, abscissa is represented signal to noise ratio (snr), and ordinate is represented synchronous correct probability, and β represents to influence the synchronous correct probability factor.Among the figure as can be seen traditional algorithm with improve algorithm under the identical β factor, the synchronous correct probability that improves algorithm will be far superior to traditional algorithm.

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

Among the figure, abscissa is represented signal to noise ratio (snr), and ordinate is represented decimal frequency bias estimation mean square error (MSE), and β represents to influence the synchronous correct probability factor.Among the figure as can be seen traditional algorithm with improve algorithm under the identical β factor, the frequency deviation of improving 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 is estimated mean square error (MSE) performance simulation figure;

Among the figure, abscissa is represented signal to noise ratio (snr), and ordinate is represented frequency deviation estimation mean square error (MSE), and β represents to influence the synchronous correct probability factor.

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

Among the figure, abscissa is represented signal to noise ratio (snr), and ordinate is represented synchronous correct probability, and β represents to influence the synchronous correct probability factor.

As can be seen, under the identical signal to noise ratio, the β factor is more big among the figure, and the synchronous correct probability of system is more high.

Embodiment

Below in conjunction with embodiment, be that the synchronous new method of Time And Frequency of a kind of effective MIMO-OFDM system is described in further detail to 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.The synchronous new method of Time And Frequency of a kind of effective MIMO-OFDM system mainly is made up of transmitting terminal and receiving terminal.At transmitting terminal, mainly comprised data source module 1, coding module 2, sign map module 3, the MIMO coding module,, the insertion pilot module 5 on each transmitting antenna, IFFT module 6 is inserted training sequence module 7, inserts protection interval module 8.Mainly comprised regularly synchronous and frequency synchronization module 9 at receiving terminal, the removal protection interval module 10 on each reception antenna, FFT module 11; 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, this module namely is the multiplexing or space diversity precoding technique in application space, and the present invention mainly adopts spatial reuse and coding techniques.Get regularly synchronous and the frequency synchronization module 9 main original positions of determining the FFT windows at receiving terminal, guarantee correctly demodulation of OFDM data symbol, mutually orthogonal property between each subcarrier of Frequency Synchronization principal security; Channel estimation module 13 mainly be utilize training sequence to multipath channel time-domain response estimate; Carry out the demodulation that MIMO decoder module 14 and decoder module 16 are realized OFDM data symbol subsequently.Fig. 2 is that the present invention inserts training sequence basic structure block diagram, training sequence is that the form with time quadrature is inserted between the OFDM symbol, but owing to be in the MIMO-OFDM system of multiple-input and multiple-output, training sequence is that the form with time quadrature is inserted between each transmitting antenna OFDM data symbol.

Fig. 3 is training sequence structure method schematic diagram of the present invention, for the MIMO-OFDM synchro system, wants receiving terminal and accurately data demodulates is come out, and is regularly particularly important synchronously.And the training sequence of constructing good autocorrelation and weak cross correlation is to guarantee that the OFDM symbol is in the synchronous important prerequisite of receiving terminal timing.The method of the training sequence structure of good autocorrelation: new training sequence T (n) of 301 structures, along with the increase of β value, its sequence self correlation strengthens in training sequence; 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); 304 sequence T (n) and T ' (n) are constituted length is the sequence C of N ₂(n).

For example: get N=32, β=10 o'clock, training sequence C ₁(n) actual sequence

Get N=32, β=10 o'clock, training sequence C ₂(n) actual sequence.

Fig. 4 be the present invention regularly synchronously and the method schematic diagram of Frequency Synchronization, the 401st, the reception signal; The 402nd, the local training sequence C of receiving terminal ₁(n) carry out cross-correlation with the reception signal, obtain regularly synchronously, synchronous timing is measured function and can be expressed as:

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

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

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

The 403rd, set threshold value, when surpassing threshold value d value, target function M (d) is judged to regularly synchronization position:

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

The 404th, determine sync bit, carry out frequency deviation and estimate that the target function that frequency deviation is estimated is expressed as:

Carry out the decimal frequency bias estimated value:

${\mathrm{\&epsiv;}}_f=\frac{1}{\mathrm{\&pi;}}\mathrm{angle}\left(R\left({\mathrm{\&tau;}}_{\mathrm{estl}}\right)\right)---\left(10\right)$

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

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

The 405th, the integer frequency bias of the laggard line frequency of decimal frequency offset compensation that estimates is estimated, the 406th, it is the ε of direct estimation under the condition of time domain that the integer frequency bias that the present invention proposes is estimated _iThereby, saved the FFT computing.The integer frequency bias estimated value:

${\mathrm{\&epsiv;}}_i={\mathrm{\&tau;}}_{\mathrm{est}2}-{\mathrm{\&tau;}}_{\mathrm{est}1}-N-\mathrm{Ng}+1---\left(12\right)$

$Q\left(d^{\&prime;}\right)=\underset{i=1}{\overset{\mathrm{Nt}}{\mathrm{\&Sigma;}}}\underset{j=1}{\overset{\mathrm{Nr}}{\mathrm{\&Sigma;}}}\left[\underset{n=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}{r}_j^{*}(d^{\&prime;}+n){\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="130522085311.png,130522085332.png"\; state="\{\{state\}\}">C</figure-callout>}}_{2,i}\left(n\right)\right]\&CenterDot;{\left[\underset{n=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}{r}_j^{*}(d^{\&prime;}+N/2-n){\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="130522085311.png,130522085332.png"\; state="\{\{state\}\}">C</figure-callout>}}_{2,i}\left(n\right)\right]}^{*}---\left(13\right)$

${\mathrm{\&tau;}}_{\mathrm{esst}2}=\arg \underset{d^{\&prime;}}{\max }\left(Q\left(d^{\&prime;}\right)\right)---\left(14\right)$

Wherein, Ng represents the length of Cyclic Prefix, C _{2, i}(.) is illustrated in second training sequence that inserts on each transmitting antenna, r _j(.) represents data signals transmitted on each reception antenna, and the search in formula (13) and (14) is with d '=τ _Est1Centered by+the N+Ng.Integer frequency bias estimated ranges ε _i∈ (N/4, N/4).

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

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

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

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

Claims (2)

1. the synchronous new method of Time And Frequency of an effective MIMO-OFDM system, its characteristic value is:

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

$T\left(n\right)=\exp \left(\frac{2\mathrm{j\&pi;r}{n}^2}{\mathrm{\&beta;N}}\right),n=\mathrm{0,1},...,N/2-1---\left(1\right)$

Wherein, get r=N/2-1, and 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 ₁(n), have:

$C_1\left(n\right)=\left\{\begin{array}{cc}T\left(n\right)& n\&Element;\&lsqb;0,N/2-1\&rsqb;\\ T(n-N/2)& n\&Element;\&lsqb;N/2,N-1\&rsqb;\end{array}---\left(2\right)\right.$

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

T′(n)=-T(N/2-n)n∈[0,N/2-1] (3)

Step 4: sequence T (n) and T ' (n) are constituted the sequence C that length is N ₂(n), have:

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

Step 5: at receiving terminal, with local training sequence C ₁(n) carry out cross-correlation with the reception signal, obtain regularly synchronously, synchronous timing is measured function and can be expressed as:

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

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

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

Wherein, Nt is transmitting terminal sky number of lines, Nr is receiving terminal sky number of lines, N is a length that does not comprise Cyclic Prefix OFDM symbol, d is integer value, and d represents the sequence that receives with respect to the relative sliding position of local sequence, and n counts for receiving signals sampling, () * represents that the data in the bracket get conjugate operation, C _{1, i}() represents first training sequence of inserting on each transmitting antenna,

Represent that data signals transmitted is got conjugate operation on each reception antenna;

Step 6: by setting simple threshold value, make target function M (d) surpass threshold value d value and be judged to regularly synchronization position, i.e. synchronization point:

${\mathrm{\&tau;}}_{\mathrm{est}1}=\arg \underset{d}{\max }\left(M\left(d\right)\right)---\left(8\right)$

Step 7: carry out the decimal frequency bias estimated value:

${\mathrm{\&epsiv;}}_f=\frac{1}{\mathrm{\&pi;}}\mathrm{angle}\left(R\left({\mathrm{\&tau;}}_{\mathrm{est}1}\right)\right)---\left(9\right)$

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

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

Step 8: estimate that with carrying out integer frequency bias behind the decimal frequency offset compensation that estimates it is direct estimation ε under the condition of time domain that integer frequency bias is estimated _i, saved the FFT computing, the integer frequency bias estimated value:

${\mathrm{\&epsiv;}}_i={\mathrm{\&tau;}}_{\mathrm{est}2}-{\mathrm{\&tau;}}_{\mathrm{est}1}-N-\mathrm{Ng}+1---\left(11\right)$

$Q\left(d^{\&prime;}\right)=\underset{i=1}{\overset{\mathrm{Nt}}{\mathrm{\&Sigma;}}}\underset{j=1}{\overset{\mathrm{Nr}}{\mathrm{\&Sigma;}}}\left[\underset{n=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}{r}_j^{*}(d^{\&prime;}+n)C_{2,i}\left(n\right)\right]\&CenterDot;{\left[\underset{n=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}{r}_j^{*}(d^{\&prime;}+N/2-n)C_{2,i}\left(n\right)\right]}^{*}---\left(12\right)$

${\mathrm{\&tau;}}_{\mathrm{est}2}=\arg \underset{d^{\&prime;}}{\max }\left(Q\left(d^{\&prime;}\right)\right)---\left(13\right)$

Wherein, Ng represents the length of Cyclic Prefix, C _{2, i}() represents second training sequence inserting on each transmitting antenna,

Represent that data signals transmitted is got conjugate operation on each reception antenna, the search in formula (12) and (13) be with

Centered by, integer frequency bias estimation range ε _i∈ (N/4, N/4).

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

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