CN100561999C - A kind of MIMO-OFDM system method for synchronous - Google Patents

Abstract

The invention discloses a kind of MIMO-OFDM method for synchronous, it is by utilizing the characteristic of IFFT conversion, training sequence with each antenna of transmitting terminal inserts arrives reception antenna signal delay not simultaneously at each transmitting antenna, still can obtain two half section identical sequences after the stack.It is slightly synchronous to carry out the time in the time domain of receiving terminal, and it is synchronously smart that frequency domain carries out the time; After the receiving end time synchronized obtains, can be easy to obtain Frequency Synchronization.Because the present invention is by being zero in the insertion idol position of making a start, strange synchronizing symbol that is training sequence can be distinguished different delay, is applicable to the distributed MIMO system.Therefore it has the realization of being easy to, and is practical, multiple advantage such as wide application; Simultaneously it to have bandwidth occupancy again few, the advantage that the availability of frequency spectrum is high.

Description

A kind of MIMO-OFDM system method for synchronous

Technical field

The invention belongs to communication technical field, it is particularly related to MIMO-OFDM (MIMO-OFDM) simultaneous techniques.

Background technology

OFDM is owing to have the message transmission rate height, and the anti-multipath interference performance is strong, and the spectrum efficiency advantages of higher more and more comes into one's own.It successfully is used for wired, radio communication.As: among DAB (Digital Audio Broadcasting), DVB, EEE802.11a and the HyperLAN/2, in the IEEE802.16 that is formulating at present, also related to the OFDM technology in a large number.This new modulation technique of OFDM also can be used in the mobile communication system of a new generation.Use the OFDM technology will improve the transmission data rate and the spectrum efficiency of the third generation mobile communication system greatly, and has good ability of anti-multipath, see document: Bingham, J.A.C., " Multicarrier modulation for data transmission:an idea whose time has come, " IEEECommunications Magazine, Volume:28 Issue:5, May 1990, Page (s): 5-14 and document: Yun Hee Kim; Iickho Song; Hong Gil Kim; Taejoo Chang; Hyung Myung Kim, " Performance analysis of a coded OFDM system in time-varyingmultipath Rayleigh fading channels; " Vehicular Technology, IEEE Transactions on, Volume:48 Issue:5, Sept.1999, Page (s): 1610-1615 is described.

One of weakness of OFDM technology be to the requirement of time and Frequency Synchronization particularly Frequency Synchronization require more much higher than single-carrier system.The general system of employing OFDM technology that requires is no more than 2% of its subcarrier spacing in the receiving terminal frequency shift (FS), sees document van de Beek, J.J.; Sandell, M.; Borjesson, P.O., " ML estimation of time and frequency offset in OFDMsystems; " Signal Processing, IEEE Transactions on, Volume:45 Issue:7, July 1997, and Page (s): 1800-1805 is described.

In the system of broadband wireless communication in future, there are two stern challenges: multidiameter fading channel and bandwidth efficiency.OFDM is by being flat channel with the frequency selectivity multidiameter fading channel in the frequency domain internal conversion, thereby reduced the influence of multipath fading.Parallel channel transmits multiplex data stream simultaneously and the MIMO technology can produce independently in the space, can increase the transmission rate of system effectively.Like this, OFDM and two kinds of technology of MIMO are combined, constitute MIMO-OFDM, just can reach two kinds of effects: a kind of is that system possesses very high transmission rate, and another kind is to reach very strong reliability by diversity.See document H.Sampath, S.Talwar, J.Tellado, et al. " A Fourth-Generation MIMO-OFDM:Broadband WirelessSystem:Design, Performance, and Field Trial Results " .IEEE Communications Magazine, Vol.40, No.9, Sept.2002, pp.143-149 is described.

One of weakness of OFDM technology is very sensitive to synchronous error, so the MIMO-OFDM system is very sensitive to synchronous error equally.In general, be divided into time synchronized and Frequency Synchronization synchronously.Under multi-path environment, OFDM requires very high to time synchronized, this also is the requirement of MIMO-OFDM system to time synchronized, the Frequency Synchronization aspect, because the MIMO-OFDM system can be considered as N parallel MIMO subsystem, therefore the ICI that introduces of frequency deviation can worsen the signal to noise ratio of each subcarrier, thereby worsens the performance of whole M IMO-OFDM communication system, sees document A.Stamoulis; S.N.Diggavi; N.Al-Dhahir, Intercarrier interference in MIMO OFDM, Signal Processing, IEEE Transactions on, Volume:50, Issue:10, Oct, 2002, pp.2451-2464 is described.In the MIMO-OFDM system, Fig. 1 is seen in the position of synchronization module.The purpose of time synchronized is to find out the border of each OFDM symbol in the serial data stream of receiving; And the purpose of Frequency Synchronization is to obtain and correct the frequency shift (FS) of receiving end.

Synchronous fast and accurately in order to obtain, synchronously often adopt the method for training sequence to finish in the MIMO-OFDM system.Consider the characteristic of MIMO-OFDM channel, some training sequences of using in the ofdm system can not be directly as the training sequence of MIMO-OFDM system, see document: Mody, A.N.Stuber, G.L.Synchronization for MIMO-OFDMsystems.Global Telecommunications Conference, 2001.GLOBECOM ' 01.IEEE, Volume:1,25-29 Nov.2001Pages:509-513 vol.1 is described.

Two kinds of usual training sequence insertion methods are arranged at present:

1) a kind of method is to adopt the training sequence of time quadrature, promptly inserts the time of training sequence and stagger mutually (as shown in Figure 2) on different transmit antennas.Training sequence on every antenna is just passable as long as satisfy strong displacement autocorrelation, and the training sequence of different antennae can be identical, and therefore design is got up more conveniently, can distinguish the time delay between each antenna.Shortcoming is the increase along with antenna number, and the also corresponding increase of the bandwidth that training sequence takies is so the availability of frequency spectrum is lower.Referring to document: T.C.W.Schenk and A.van Zelst.Frequency Synchronization for MIMO-OFDMWireless LAN Systems.Proc.IEEE Vehicular Technology Conference Fall 2003 (VTC Fall 2003), Orlando (FL), 6-9 October 2003, paper 05D-03 is described.

2) another kind of method is the training sequence of each transmitting antenna at same position insertion quadrature, can strengthen the ability of training sequence anti-multipath decline by means such as multistage repeat.These sequences are satisfying under the prerequisite of quadrature, also must satisfy the displacement autocorrelation (as shown in Figure 3) of training sequence.It is identical that this algorithm supposes that all transmitting antennas arrive the time delay of all reception antennas, and frequency shift (FS) is identical, promptly only has a time migration and a frequency shift (FS) between the transmitting-receiving.Obviously, this algorithm can not solve when the asynchronous stationary problem of each road antenna arrival time delay.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.2001 Pages:509-513 vol.1 is described.

Summary of the invention

The object of the present invention is to provide a kind of MIMO-OFDM (MIMO-OFDM) method for synchronous, it is synchronous that it utilizes training sequence to carry out MIMO-OFDM, has to be easy to realize, practical, wide application can be distinguished characteristics such as many antennas time delay, availability of frequency spectrum height.

In order to describe the content of this paper easily, at first make term definition:

FFT/IFFT: fast fourier transform/invert fast fourier transformation

Cyclic Prefix (CP): because the ICI that causes of multipath, the signal of inserting in its protection at interval is the duplicating of aft section signal of OFDM symbol itself to the OFDM symbol in order to eliminate.

Framing: the base unit of transfer of data, data and redundant information are arranged by certain specification, send again.

The invention provides a kind of training sequence that utilizes and carry out the synchronous method of MIMO-OFDM, it by make a start and receiving end two parts form, concrete steps are as follows:

Make a start to the treatment step that transmits following (as shown in Figure 4):

Step 1: the number of definition transmitting antenna is M, and M gets positive integer, and the number of M is greater than 1; Select M the long N that is ₁PN sequence b _m[k], N ₁Get positive integer; With this PN sequence b _m[k] afterbody adds one " 1 ", and constituting length is the sequence c of Q _m(k), k ∈ [0, Q-1], m ∈ [1, M]; The c of this moment _m(k) value is plural form, i.e. c _m(k) ∈ { 1+j ,-1-j};

Step 2: the sequence c that step 1 is obtained _m(k) carry out zero insertion and handle, generate the training sequence T of each antenna emission _m(i), i ∈ [0, N-1], N are that the FFT of ofdm system counts, and get positive integer; The specific practice that zero insertion is handled is: sequence c ₁(k) first information c ₁(1), is inserted into the training sequence T of first transmitting antenna ₁(i) first; Sequence c ₁(k) second information c ₁(2), be inserted into training sequence T ₁(i) 2M+1 position; The 3rd information c ₁(3) be inserted into T ₁(i) 4M+1 position, by that analogy, up to k information c ₁(k) be inserted into T ₁(i) the 2nd (Q-1) M+1 position, training sequence T ₁(i) all the other positions are zero insertion all; For second transmitting antenna, sequence c ₂(k) first information c ₂(1), is inserted into corresponding training sequence T ₂(i) the 3rd; Sequence c ₂(k) second information c ₂(2), be inserted into training sequence T ₂(i) 2M+3 position; The 3rd information c ₂(3) be inserted into training sequence T ₂(i) 4M+3 position, by that analogy, up to k information c ₂(k) be inserted into T ₂(i) the 2nd (Q-1) M+3 position, training sequence T ₂(i) all the other positions are zero insertion all; By that analogy, sequence c _M(k) first information c _M(1), is inserted into the training sequence T of first transmitting antenna _M(i) 2M-1 position; Sequence c _M(k) second information c _M(2), be inserted into training sequence T _M(i) 2M+2M-1 position; The 3rd information c _M(3) be inserted into T _M(i) 4M+2M-1 position, by that analogy, up to k information c _M(k) be inserted into T _M(i) the 2nd (Q-1) M+2M-1 position, training sequence T _M(i) all the other positions are zero insertion all, as formula (1) and shown in Figure 5; Must satisfy between N here and the number of transmit antennas M: N=2MQ;

Step 3: the training sequence T that step 2 is obtained _m(i) the corresponding data sequence 1 of inserting is in data sequence m; Concrete insertion method is: training sequence T ₁(i) be inserted in the data sequence 1 on first antenna training sequence T ₂(i) be inserted in second data sequence 2 on the antenna, by that analogy, up to training sequence T _M(i) be inserted among M the data sequence M on the antenna; T _m(i) position of inserting each antenna data sequence all is identical, sequence after will inserting is then carried out the IFFT computing, and the result who obtains adds Cyclic Prefix (CP) again and handles, the result who obtains like this launches (as shown in Figure 4) by each radio-frequency antenna after carrying out the framing processing again;

Receiving end treatment step to received signal following (as shown in Figure 6):

Step 4: on the reception antenna of p road, with the sequence of the emission of making a start that receives, by the size sliding window that is N, p ∈ [1, P], P is the reception antenna number, gets positive integer, and greater than 1; With the data r in the window _iBe divided into former and later two half section, preceding half section is r _i, 0≤i≤N/2-1, the second half section is r _i, N/2≤i≤N-1; The information of these two and half sections sequence front τ length is all removed, asked relevant, obtain correlation φ (d) with the information correspondence of back, the skew of d express time, get positive integer:

$\mathrm{\φ}\left(d\right)=\underset{i=\mathrm{\τ}}{\overset{N/2-1}{\mathrm{\Σ}}}(r_{d+i}^{*}\·r_{d+N/2+i})---\left(2\right)$

Step 5: the correlation φ (d) that step 4 is obtained carries out normalized, obtains a relevant peaks M (d) (as shown in Figure 7):

$M\left(d\right)=\frac{2\·\left|\mathrm{\φ}\left(d\right)\right|}{{\left(R\left(d\right)\right)}^2}---\left(3\right)$

Wherein, the information power sum of R (d) for carrying out formula (2) computing

$R\left(d\right)=\underset{i=\mathrm{\τ}}{\overset{N/2-1}{\mathrm{\Σ}}}{\left|r_{d+i}\right|}^2+\underset{i=\mathrm{\τ}+N/2}{\overset{N-1}{\mathrm{\Σ}}}{\left|r_{d+i}\right|}^2---\left(4\right)$

Step 6: be provided with one then and declare thresholding firmly and length is the sliding window of N, will surpass the sequence that the time migration of thresholding put in the pairing sliding window and begin from relevant peaks M (d), the sequence that is N with L length is selected continuously, and establishing this section sequence is g _i(t), i=0,1 ..., L-1, t=0,1 ..., N-1; The time migration point that record surpasses thresholding is

, L gets positive integer, and its value is greater than 1;

Step 7: L the sequence g that length is N that step 6 is obtained _i(t), carry out the FFT computing respectively, obtain G _i(k), i=0,1 ..., L-1, k=0,1 ..., N-1:

$G_i\left(k\right)=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{g}_i\left(n\right)e^{-2\mathrm{\πjnk}/N}---\left(5\right)$

Step 8: the sequence G that step 7 is obtained then _i(k), according to the mode of inserting training sequence in the step 2 of making a start, the information extraction of correspondence position is come out, concrete extraction mode is: the information that detects first via transmission antennas transmit arrives the smart synchronous points of time of p road reception antenna, with G _i(k) in first, the 2M+1 position, come out to the 2nd (Q-1) M+1 position information extraction by that analogy in the 4M+1 position; The information that detects the second tunnel transmission antennas transmit arrives the smart synchronous points of time of p road reception antenna, with G _i(k) in the 3rd, the 2M+3 position, come out to the 2nd (Q-1) M+3 position information extraction by that analogy in the 4M+3 position; By that analogy, the information that detects M road transmission antennas transmit arrives the smart synchronous points of time of p road reception antenna, with G _i(k) 2M-1 position in, the 2M+2M-1 position, come out to the 2nd (Q-1) M+2M-1 position information extraction by that analogy in the 4M+2M-1 position; With local sequence c _m(k) be correlated with and multiply each other, just can obtain the smart synchronous points of time of m road transmitting antenna signal

${\widehat{\mathrm{\θ}}}_{2,m,p}=\underset{i}{\arg \max }\{\underset{j=0}{\overset{Q-1}{\mathrm{\Σ}}}{G}_i^{*}(2m-1+2\mathrm{jM})\·c_m\left(j\right)\}---\left(6\right)$

Wherein, G _i ^*(2m-1+2jM) expression is to G _i(2m-1+2jM) ask the result of conjugation.

Step 9: the time migration point that step 6 is obtained Smart synchronous points of the time that obtains with step 8

Summation, the signal that obtains m road transmission antennas transmit arrives the time synchronized point of p road reception antenna:

${\widehat{\mathrm{\θ}}}_{m,p}={\widehat{\mathrm{\θ}}}_{1,p}+{\widehat{\mathrm{\θ}}}_{2,m,p}---\left(7\right)$

Step 10: after obtaining time synchronized point by step 9, adjusted information of the time that obtains; Again adjusted information of time is carried out Frequency Synchronization, obtain the information after Frequency Synchronization is handled; Information after then Frequency Synchronization being handled goes Cyclic Prefix (CP) to handle; The information after Cyclic Prefix (CP) is handled of will going is carried out the FFT processing again.

Need to prove, consider M road antenna relative delay difference, with former and later two half section information of all removing front τ length of the data in the window.τ 〉=D in the receiving end step 1 _p, establish d _mThe relative time delay that the expression reception antenna is received each road transmitting antenna signal, D _p=max{d ₁, d ₂..., d _m.In addition, in the treatment step of receiving end, are thick Synchronous Processing of time from step 1 to step 3, from step 4 to step 5 smart Synchronous Processing of time.

The present invention is that a kind of training sequence that utilizes carries out the synchronous method of MIMO-OFDM, it is characterized in that: the frequency domain of making a start, and the training sequence of each antenna is placed apart, is used for distinguishing different delay, and the time of can carrying out is synchronously smart; The time domain of receiving end, these training sequences placed apart have identical two and half sections again through the IFFT conversion after the stack.So a search window is set, carries out the auto-correlation computation of former and later two half section sequence.A threshold value is set, and record surpasses the time migration point of this threshold value, thick synchronous points of the time of obtaining.To get one section FFT computing of sliding above the sequence of this thresholding then, obtain the multistage sequence of frequency domain then.Afterwards the information of the correspondence position in the multistage sequence is taken out, carry out related operation, when obtaining peak-peak, promptly think to have obtained smart synchronous points of time with local training sequence.After the time synchronized point finds, carry out Frequency Synchronization again.

Innovation part of the present invention has been to utilize the characteristic of IFFT conversion, thereby with the training sequence that each antenna of transmitting terminal inserts, arrives reception antenna signal delay not simultaneously at each transmitting antenna, still can obtain two half section identical sequences after the stack.So it is slightly synchronous to carry out the time in the time domain of receiving terminal, it is synchronously smart that frequency domain carries out the time; After the receiving end time synchronized obtains, can be easy to obtain Frequency Synchronization.Aspect time synchronized, the present invention has considered that each transmitting antenna arrives the situation that time delay has nothing in common with each other, and therefore has more broad sense, applicable to the distributed MIMO system.

Foundation of the present invention is:

1) because training sequence is known, as the training sequence b[k that selects] when having good autocorrelation performance, be easy to realize time and the Frequency Synchronization of OFDM.

2) owing to idol position in the synchronizing symbol is zero, strange training sequence that is insertion.At the frequency domain of transmitting terminal, if pseudo random sequence is inserted in the strange position of training sequence, the idol position inserts zero, so through just obtaining former and later two half section identical sequences after the IFFT.So the insertion method of our training sequence can guarantee can obtain two half section identical sequences after the training sequence process IFFT on the M bar transmitting antenna.Therefore even the time delay that arrives reception antenna when each transmitting antenna is not simultaneously, reception antenna still can obtain two identical half section sequences (as shown in Figure 8).Here establish t _m(i) be corresponding T _m(i) through the IFFT calculated result, establish a _i, b _i, c _iBe respectively t ₁(i), t ₂(i), t ₃(i) sequence.d ₂, d ₃Be respectively t ₂(i), t ₃(i) sequence is with respect to t ₁(i) delay.Work as d ₃During for maximum delay, after superposeing according to the mode among the figure, two and half sections sequences 1 and 2 are identical.

3), can utilize two half section identical sequences to carry out synchronously thick and Frequency Synchronization of time according to above-mentioned principle.Because the training sequence that previous each antenna inserts, the position all separates.Therefore, to surpassing the sequence of thresholding, the FFT computing of sliding is carried out related operation with local training sequence at receiving terminal then, can obtain maximum peak, smart Synchronous Processing of the time of carrying out.

The present invention has following feature:

The training sequence of 1, making a start adds one " 1 " by certain PN sequence through afterbody and constitutes;

2, make a start that the idol position is zero in the synchronizing symbol, strange position is the training sequence of insertion, and the training sequence of each antenna is placed apart, is used for distinguishing different delay;

3, make a start the synchronizing symbol of each transmitting antenna at frequency domain, its position all is identical.

4, it is synchronously smart that the time synchronized of receiving end is divided the time synchronously thick and frequency domain time of time domain.

5, receiving end will receive earlier data carry out before the second half section auto-correlation, thick synchronous points of the time that obtains.Again will be above the FFT computing of sliding of the sequence of thresholding, extract partial information then and local training sequence carries out cross-correlation, smart synchronous points of the time that obtains.

6, thick synchronous target function of the time of receiving end, be each correlation of in search window, calculating accumulated value square, carry out the result of normalized then.

7, smart synchronous target function of the time of receiving end, be each correlation of calculating in the search window accumulated value square.The invention has the beneficial effects as follows:

By being zero in the insertion idol position of making a start, strange synchronizing symbol that is training sequence can be distinguished different delay, is applicable to the distributed MIMO system.Therefore it has the realization of being easy to, and is practical, multiple advantage such as wide application; Simultaneously it to have bandwidth occupancy again few, the advantage that the availability of frequency spectrum is high.

Description of drawings

Fig. 1 is general MIMO-OFDM system block diagram

Wherein, 1 is string and modular converter, and 2 is modulation module, 3 processing modules when being empty, 4 is the IFFT conversion module, 5 for adding the cyclic prefix CP module, 6 is the framing module, 7 is synchronization module, and 8 for separating frame module, and 9 for going the cyclic prefix CP module, 10 is the FFT conversion module, 11 is channel estimation module, 12 processing modules when being empty, and 13 is the turbo receiver module;

Fig. 2 utilizes the training sequence of time quadrature to carry out the synchronous schematic diagram of MIMO-OFDM

Among the figure, receiving end adds up the conjugate multiplication of the corresponding position of two sections sequences that receives on each antenna, obtains target function value; Wherein, TX1 represents that the training sequence that inserts on first transmit antennas, TX2 represent the training sequence that inserts on first transmit antennas; They all have 2N _TrainLong space, what wherein the first half of TX1 inserted is training sequence, what latter half inserted is zero; What the first half of TX2 inserted is zero, and what latter half inserted is training sequence; The training sequence that inserts on two transmitting antennas all is identical, all is that a segment length is 2N _gThe protection prefix, the length that is two sections repetitions then is N _cTraining sequence;

Fig. 3 carries out the synchronous schematic diagram of MIMO-OFDM for the training sequence that inserts quadrature in same position

Among the figure, it is N that Q length that repeats is arranged _IPilot frequency sequence, their prefix length is G;

Fig. 4 inserts schematic diagram for the synchronizing symbol of making a start

Among the figure, the position of inserting training sequence is before the IFFT conversion; Wherein, 1 is string and modular converter, and 4 is the IFFT conversion module, and 5 for adding the cyclic prefix CP module, and 6 is the framing module;

Fig. 5 constitutes the synchronizing symbol schematic diagram for each antenna training sequence of making a start inserts

Wherein, T ₁(i) be the training sequence that inserts on first transmit antennas, T ₂(i) be the training sequence that inserts on first transmit antennas, T ₃(i) be the training sequence that inserts on first transmit antennas; T ₁(i) in, c ₁(1) is sequence c ₁(k) first information, c ₁(2) be sequence c ₁(k) second information, c ₁(3) be sequence c ₁(k) the 3rd information; T ₂(i) in, c ₂(1) is sequence c ₂(k) first information, c ₂(2) be sequence c ₂(k) second information, c ₂(3) be sequence c ₂(k) the 3rd information; T ₃(i) in, c ₃(1) is sequence c ₃(k) first information, c ₃(2) be sequence c ₃(k) second information; M is a number of transmit antennas;

Fig. 6 is the synchronous schematic flow sheet of receiving end

Wherein, 9 for going the cyclic prefix CP module, and 10 is the FFT conversion module;

Fig. 7 be the receiving end time thick synchronously in, the relevant peaks schematic diagram that obtains

Wherein, the normalized relevant peaks M (d) that curve representation is obtained by step 5, threshold value is declared in amplitude 0.8 expression firmly;

Fig. 8 is in the present invention's foundation, under each transmitting antenna time delay different situations, and two half section identical sequence schematic diagrames that receiving end obtains

Wherein, t ₁(i) sequence of first transmission antennas transmit of obtaining of expression reception antenna, t ₂(i) sequence of second transmission antennas transmit obtaining of expression reception antenna, t ₃(i) sequence of the 3rd transmission antennas transmit obtaining of expression reception antenna; a ₁To a ₇The sequence t that expression receives ₁(i) information; b ₁To b ₇The sequence t that expression receives ₂(i) information; c ₁To c ₇The sequence t that expression receives ₃(i) information; d ₂Represent second sequence that transmission antennas transmit is gone out, compare the sequence that first transmission antennas transmit is gone out, arrive the time delay of reception antenna; d ₃Represent the 3rd sequence that transmission antennas transmit is gone out, compare the sequence that first transmission antennas transmit is gone out, arrive the time delay of reception antenna;

Embodiment

Provide the concrete MIMO-OFDM configuration implementation method of this patent down below.Need to prove: the parameter in the following example does not influence the generality of this patent.

If the useful symbol lengths of OFDM is N=2048.The MIMO model is four four receipts, i.e. M, and P is 4.No. four transmitting antennas are respectively 0,5,10,15 sampled points to relative time delay of reception antenna.So the τ in the defined formula 2 is 20 sampled points.

One, make a start:

Select four sections PN sequences, its cycle is 255 m sequence, is designated as b _m[k] k ∈ [1,255], afterbody obtain c after adding one " 1 " _m(k) k ∈ [1,256] m ∈ [1,4], c _m(k) ∈ { 1+j ,-1-j}.Mode according to formula 1 is inserted, and obtains the synchronizing symbol T of four transmitting antennas _m(i) i ∈ [0, N-1].

Two, receiving end

It is 2048 sliding window by a size that receiving end will receive data, according to formula 2 calculating target functions, after functional value is greater than default thresholding 0.8, has promptly obtained thick synchronous points of time in this window

, the sequence that to obtain 250 length then be N, establishing this section sequence is g _i(t), i=0,1 ..., L-1, t=0,1 ..., N-1.According to formula 5, obtain frequency domain information G then _i(k), carry out and local sequence related operation according to formula 6, smart synchronous points of the time that obtains is so thick smart synchronous points, just can obtain total time synchronized point according to formula 7 again.

Claims (1)

1, a kind of MIMO-OFDM method for synchronous, it by make a start and receiving end two parts form, concrete steps are as follows:

It is as follows to the treatment step that transmits to make a start:

Step 1: the number of definition transmitting antenna is M, and M gets positive integer, and the number of M is greater than 1; Select M the long N that is ₁PN sequence b _m[k], N ₁Get positive integer; With this PN sequence b _m[k] afterbody adds one " 1 ", and constituting length is the sequence c of Q _m(k), k ∈ [0, Q-1], m ∈ [1, M]; The c of this moment _m(k) value is plural form, i.e. c _m(k) ∈ { 1+j ,-1-j};

Step 2: the sequence c that step 1 is obtained _m(k) carry out zero insertion and handle, generate the training sequence T of each antenna emission _m(i), i ∈ [0, N-1], N are that the FFT of ofdm system counts, and get positive integer; The specific practice that zero insertion is handled is: sequence c ₁(k) first information c ₁(1), is inserted into the training sequence T of first transmitting antenna ₁(i) first; Sequence c ₁(k) second information c ₁(2), be inserted into training sequence T ₁(i) 2M+1 position; The 3rd information c ₁(3) be inserted into T ₁(i) 4M+1 position, by that analogy, up to k information c ₁(k) be inserted into T ₁(i) the 2nd (Q-1) M+1 position, training sequence T ₁(i) all the other positions are zero insertion all; For second transmitting antenna, sequence c ₂(k) first information c ₂(1), is inserted into corresponding training sequence T ₂(i) the 3rd; Sequence c ₂(k) second information c ₂(2), be inserted into training sequence T ₂(i) 2M+3 position; The 3rd information c ₂(3) be inserted into training sequence T ₂(i) 4M+3 position, by that analogy, up to k information c ₂(k) be inserted into T ₂(i) the 2nd (Q-1) M+3 position, training sequence T ₂(i) all the other positions are zero insertion all; By that analogy, sequence c _M(k) first information c _M(1), is inserted into the training sequence T of first transmitting antenna _M(i) 2M-1 position; Sequence c _M(k) second information c _M(2), be inserted into training sequence T _M(i) 2M+2M-1 position; The 3rd information c _M(3) be inserted into T _M(i) 4M+2M-1 position, by that analogy, up to k information c _M(k) be inserted into T _M(i) the 2nd (Q-1) M+2M-1 position, training sequence T _M(i) all the other positions are zero insertion all; Must satisfy between N here and the number of transmit antennas M: N=2MQ;

Step 3: the training sequence T that step 2 is obtained _m(i) the corresponding data sequence 1 of inserting is in data sequence m; Concrete insertion method is: training sequence T ₁(i) be inserted in the data sequence 1 on first antenna training sequence T ₂(i) be inserted in second data sequence 2 on the antenna, by that analogy, up to training sequence T _M(i) be inserted among M the data sequence M on the antenna; T _m(i) position of inserting each antenna data sequence all is identical, and the sequence after will inserting is then carried out the IFFT computing, and the result who obtains adds cyclic prefix CP again and handles, and the result who obtains like this carries out being launched by each radio-frequency antenna after framing handles again;

Receiving end treatment step to received signal is as follows:

Step 4: on the reception antenna of p road, with the sequence of the emission of making a start that receives, by the size sliding window that is N, p ∈ [1, P], P is the reception antenna number, gets positive integer, and greater than 1; With the data r in the window _iBe divided into former and later two half section, preceding half section is r _i, 0≤i≤N/2-1, the second half section is r _i, N/2≤i≤N-1; The information of these two and half sections sequence front τ length is all removed, asked relevant, obtain correlation φ (d) with the information correspondence of back, the skew of d express time, get positive integer:

$\mathrm{\φ}\left(d\right)=\underset{i=\mathrm{\τ}}{\overset{N/2-1}{\mathrm{\Σ}}}(r_{d+i}^{*}\·r_{d+N/2+i})---\left(2\right)$

Step 5: the correlation φ (d) that step 4 is obtained carries out normalized, obtains a relevant peaks M (d):

$M\left(d\right)=\frac{2\·\left|\mathrm{\φ}\left(d\right)\right|}{{\left(R\left(d\right)\right)}^2}---\left(3\right)$

Wherein, the information power sum of R (d) for carrying out formula (2) computing

$R\left(d\right)=\underset{i=\mathrm{\τ}}{\overset{N/2-1}{\mathrm{\Σ}}}{\left|r_{d+i}\right|}^2+\underset{i=\mathrm{\τ}+N/2}{\overset{N-1}{\mathrm{\Σ}}}{\left|r_{d+i}\right|}^2---\left(4\right)$

Step 6: be provided with one then and declare thresholding firmly and length is the sliding window of N, will surpass the sequence that the time migration of thresholding put in the pairing sliding window and begin from relevant peaks M (d), the sequence that is N with L length is selected continuously, and establishing this section sequence is g _i(t), i=0,1 ..., L-1, t=0,1 ..., N-1; The time migration point that record surpasses thresholding is

, L gets positive integer, and its value is greater than 1;

Step 7: L the sequence g that length is N that step 6 is obtained _i(t), carry out the FFT computing respectively, obtain G _i(k), i=0,1 ..., L-1, k=0,1 ..., N-1:

$G_i\left(k\right)=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{g}_i\left(n\right)e^{-2\mathrm{\πjnk}/N}---\left(5\right)$

Step 8: the sequence G that step 7 is obtained then _i(k), according to the mode of inserting training sequence in the step 2 of making a start, the information extraction of correspondence position is come out, concrete extraction mode is: the information that detects first via transmission antennas transmit arrives the smart synchronous points of time of p road reception antenna, with G _i(k) in first, the 2M+1 position, come out to the 2nd (Q-1) M+1 position information extraction by that analogy in the 4M+1 position; The information that detects the second tunnel transmission antennas transmit arrives the smart synchronous points of time of p road reception antenna, with G _i(k) in the 3rd, the 2M+3 position, come out to the 2nd (Q-1) M+3 position information extraction by that analogy in the 4M+3 position; By that analogy, the information that detects M road transmission antennas transmit arrives the smart synchronous points of time of p road reception antenna, with G _i(k) 2M-1 position in, the 2M+2M-1 position, come out to the 2nd (Q-1) M+2M-1 position information extraction by that analogy in the 4M+2M-1 position; With local sequence c _m(k) be correlated with and multiply each other, just can obtain the smart synchronous points of time of m road transmitting antenna signal

${\widehat{\mathrm{\θ}}}_{2,m,p}=\underset{i}{\arg \max }\{\underset{j=0}{\overset{Q-1}{\mathrm{\Σ}}}{G}_i^{*}(2m-1+2\mathrm{jM})\·c_m\left(j\right)\}---\left(6\right)$

Wherein, G _i ^*(2m-1+2jM) expression is to G _i(2m-1+2jM) ask the result of conjugation;

Step 9: the time migration point that step 6 is obtained

Smart synchronous points of the time that obtains with step 8

Summation, the signal that obtains m road transmission antennas transmit arrives the time synchronized point of p road reception antenna:

${\widehat{\mathrm{\θ}}}_{m,p}={\widehat{\mathrm{\θ}}}_{1,p}+{\widehat{\mathrm{\θ}}}_{2,m,p}---\left(7\right)$

Step 10: after obtaining time synchronized point by step 9, adjusted information of the time that obtains; Again adjusted information of time is carried out Frequency Synchronization, obtain the information after Frequency Synchronization is handled; Information after then Frequency Synchronization being handled goes cyclic prefix CP to handle; Carry out the FFT processing again with going the information after cyclic prefix CP is handled.

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