CN101083647B - Method for realizing synchronization in multi-input multi-output OFDM system - Google Patents

Abstract

The method includes following steps: constructing leading / synchronizing sequence on each transmission antenna, as well as carrying out framing and sending operations; carrying out once time synchronization by combining with cycling prefix information on each receiving antenna; using the leading symbols to carry out frequency deviation estimation (FDE) in time domain in integral multiple and decimal multiple for each receiving antenna; merging in equal gain for value of FDE on each receiving antenna so as to obtain final average value of FDE, and carrying out compensation of FDE for data of each receiving antenna; using leading symbol to carry out second synchronization for time; selecting best point of second synchronization for time; using the obtained best point to carry out synchronous post-processing. Satisfying precision required by operation, the invention raises SNR for received signal, does not use too much system resources, and increase redundancy of system, etc.

Description

Realize synchronous method in a kind of multi-input multi-output orthogonal frequency division multiplexing system

Technical field

The present invention relates to a kind of multiple-input and multiple-output (MIMO) OFDM (OFDM) system, relate in particular to and realize synchronous method in a kind of MIMO+OFDM system, belong to wireless or the wire communication field.

Background technology

Many antennas multiple-input and multiple-output (MIMO) is a kind of Radio Transmission Technology efficiently that grew up in recent years, is meant and uses a plurality of transmitting antennas and reception antenna respectively at transmitting terminal and receiving terminal.Traditional communication system is singly to enter singly to go out the SISO system, advancing singly to go out the MISO mode more and singly advancing to have more the special circumstances that the SIMO mode also is MIMO based on transmit diversity and receive diversity.The basic thought of MIMO is in emission, receives or the transmitting-receiving both-end adopts a plurality of antennas, and treatment technology during by sky makes full use of the independent fading characteristic of interchannel, improves the availability of frequency spectrum, communication quality and power system capacity.For example: people such as the Foschini of Bell Laboratory, a kind of layered space-time architecture (BLAST) has been proposed, it is divided into several sub data flows with the information source data, independently carries out coded/modulated.The demixing time space system can reach the bandwidth availability ratio of 42b/s/Hz under the average signal-to-noise ratio of 21dB, such bandwidth availability ratio is inconceivable for single-antenna transmission single antenna receiving system.

OFDM is divided into the subchannel of several quadratures to frequency spectrum at frequency domain, and the carrier wave of each subchannel is overlapped, has improved the availability of frequency spectrum.Because therefore the bandwidth relative narrower of each subchannel is flat fading to whole transmitted bandwidth signal frequency-selective channel for each sub-channel signal, equilibrium can be carried out respectively each subcarrier, has simplified receiver structure greatly.Because OFDM has availability of frequency spectrum height, balanced simple advantage, is very suitable for wired and wireless transmission at a high speed, has therefore obtained broad research.

The feasible demand to frequency spectrum of the surge of high speed business and number of users sharply increases, and frequency spectrum resource is limited, so we are in conjunction with MIMO and these two advanced persons' of OFDM technology, can improve the availability of frequency spectrum on the one hand, can effectively resist frequency selective fading on the other hand.

But MIMO and OFDM are combined in when having above advantage, and do not eliminate they self shortcoming: OFDM is very responsive to frequency shift (FS).In order to adopt the OFDM technology, carrier deviation is compared with subcarrier spacing, must be very little, otherwise the demodulation performance of OFDM will be subjected to very big influence.Yet there is time variation in wireless channel, the frequency shift (FS) of wireless signal can appear in transmission course, Doppler frequency shift for example, the perhaps frequency departure that exists between transmitter carrier frequency and the receiver local oscillator, the capital makes that the orthogonality between the ofdm system subcarrier is destroyed, thereby causes the signal between the subchannel to interfere with each other (ICI).Simultaneously, the symbol timing of ofdm system must drop in the scope that Cyclic Prefix (CP) allows, otherwise at this moment the FFT demodulation window has comprised the information of non-current code element, will cause the interference between code element.And it is regularly synchronous for the MIMO+OFDM system, also can adopt known information to analyze synchronously, as CP information, be current popular processing method, can not need the extra resource of system to realize that synchronously, amount of calculation is also little simultaneously based on CP information.But it is comparatively smooth that its shortcoming is a relevant peaks, is unfavorable for judgement, and frequency offset estimation range is little simultaneously.So, generally only as timing coarse synchronization.In addition, utilize the special construction of pilot tone/synchronizing symbol to carry out the synchronously smart of timing.Frequency Synchronization adopts special leading design to carry out synchronously.As the Chinese application number of Samsung: 200410010473.6 on October 16th, 2004 application, publication number: CN 1630283A patent is carried out timing coarse synchronization for the leading method of launching has synchronously proposed employing CP, is utilized crossing dependency to carry out the timing essence synchronously in multi-input multi-output-orthogonal frequency-division multiplexing system, utilize orthogonal sequence (CAZAC) to constitute leading according to certain special construction then.The use of this method can regularly smart synchronously in the complex operation of complexity change into simple addition and conversion, and performance for estimating channel is better than traditional method.But the precision of frequency offset estimating is limited, and each antenna need repeat to send identical targeting sequencing, has increased a large amount of complexities.For the precise time synchronous points that finds, handle in addition, can increase the signal to noise ratio of received signal, improve the performance of system if do some.

Paolo Priotti equals the US publication of application on August 22nd, 2003: the synchronous method and apparatus of US2005041693A1 patent MIMO+OFDM wireless communication system medium frequency has proposed to adopt and has obtained one group of weights by received signal SNR, and is weighted on corresponding received signal when Frequency Synchronization.The thought that this method utilizes high specific to merge is carried out Frequency Synchronization, need be before estimating frequency deviation the training symbol that receives of every antenna be weighted according to the weights that their SNR calculates.This method perhaps under the fast fading channel low signal-to-noise ratio situation, can obtain Frequency Synchronization preferably under the situation that channel condition information (CSI) is not provided.But this is to get in return with the cost of a large amount of operand of weights calculating, and the realizability of this method is relatively poor simultaneously.Therefore, there is defective in prior art, awaits further improving and development.

Summary of the invention

Technical problem to be solved by this invention is to provide the synchronous method of realization in a kind of multi-input multi-output orthogonal frequency division multiplexing system, thereby make the MIMO+OFDM receiving system under with the cost of small system resources, realize symbol synchronization by low complexity algorithm, and added time synchronized post-processing module, just utilized another kind of method to replace the method for the existing CP of going, do not increase complexity, but but make the performance of receiver obtain obvious improvement.

For solving the problems of the technologies described above, the invention provides the synchronous method of realization in a kind of multi-input multi-output orthogonal frequency division multiplexing system, comprise the steps:

(1) leading/synchronizing sequence of transmitting terminal structure is also launched the leading/synchronizing sequence on the every transmitting antenna of orthogonal frequency division multiplexing data symbols on the different transmitting antennas and described structure behind the framing respectively simultaneously;

(2) based on many reception antennas, utilize Cyclic Prefix in the OFDM symbol to carry out the relevant of significant character length, the correlated results that obtains carries out the time domain single treatment to the correlated series energy, obtains the set of optimal synchronisation point after subsynchronous;

(3) time one minor synchronous point that obtains based on every reception antenna carries out the time domain frequency offset estimating based on leading/synchronizing sequence respectively;

(4) result of the time domain frequency offset estimating value that obtains on the every reception antenna united carry out equal gain combining, obtain a final averaged frequency offset estimated value after, use this result respectively the data on the every reception antenna to be carried out compensate of frequency deviation;

(5) on every reception antenna, respectively in the range of convergence of the synchronous points of a subsynchronous output, the leading symbol that receiving terminal behind the compensate of frequency deviation is obtained and the leading symbol of described transmission carry out the time domain cross-correlation, and it is surplus to utilize maximum that circulating prefix-length is got, and obtains time second synchronization point;

(6) correlation peak of all reception antennas is made comparisons, the time synchronized point of choosing main peak value and that root antenna of the ratio maximum of minor peaks is as Best Times second synchronization point;

(7) find Best Times second synchronization point after, to the reception data of every transmitting antenna, utilize the signal post-processing after the time domain circular convolution characteristic of OFDM is carried out precise synchronization.

Wherein, step (1) described leading/synchronizing sequence must construct on every transmit antennas of transmitting terminal, comprises Cyclic Prefix and PN sequence, targeting sequencing comprise one synchronously/leading symbol.

Described leading symbol is made of the identical repetition PN sequence of length.

The length of described PN sequence is integral multiple/one of efficient orthogonal frequency division multiplexing data length.

Wherein, the relevant of the described significant character length of step (2) represented with following formula:

$b\left(k\right)=\underset{m=0}{\overset{P-1}{\mathrm{\Σ}}}r{(m+k)r}^{*}(m+k+N)$

Wherein, P represents the length of Cyclic Prefix symbol, and r is a receiving sequence.

The described time domain single treatment of step (2) is to do same processing on every reception antenna, choose greater than peaked half and less than peaked any one the number as decision threshold.

Wherein, described step (3) comprises, corresponding to every reception antenna, utilize first synchronous points in the time one minor synchronous point set, thresholding slip conjugate multiplication is carried out frequency offset estimating with available leading symbol when carrying out, estimation range is at [N/2, N/2], wherein N is the number of times that leading symbol repeats on time domain, chooses according to the frequency deviation size that reality produces.Wherein, described frequency offset estimating is represented with following formula:

${\hat{f}}_{\mathrm{\Δ}}=\frac{\mathrm{angle}\left(z\right)}{2\mathrm{\π}{N}_S{T}_S}$

Wherein, T _SBe OFDM symbol period, N _SRepresent leading/the length of repetitive sequence on time domain that synchronizing sequence adopted, z represents with following formula:

$z=\underset{n=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{r}_n{r}^{*}(n+N_S)=\underset{n=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{S}_n{e}^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H06183217920060601E000032.png,H06183217920060601E000041.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{f}_{\mathrm{\&Delta;}}n{T}_S}{S}^{*}(n+N_S)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H06183217920060601E000032.png,H06183217920060601E000041.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{f}_{\mathrm{\&Delta;}}(n+N_S)T_S}$

$=e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H06183217920060601E000032.png,H06183217920060601E000041.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{f}_{\mathrm{\&Delta;}}{N}_S{T}_S}\underset{n=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\left|S_n\right|}^2$

Wherein, r is the targeting sequencing after subsynchronous through that receives, $S_n=r_n{e}^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H06183217920060601E000032.png,H06183217920060601E000041.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{f}_{\mathrm{\&Delta;}}n{T}_S},$ T _SBe the OFDM symbol period.

Wherein, the described equal gain combining of step (4) is represented with following formula:

$\stackrel{\&OverBar;}{\mathrm{Freq}\_\mathrm{Offset}}=(1/N_R)*\underset{i=1}{\overset{N_R}{\mathrm{\&Sigma;}}}\mathrm{Freq}\_\mathrm{Offset}\left(i\right)$

Wherein, N _RBe the reception antenna number, Freq_Offset (i) is the frequency offset estimating value of i root reception antenna.

Wherein, the described leading symbol that receiving terminal behind the compensate of frequency deviation is obtained of step (5) and the leading symbol of described transmission carry out the time domain cross-correlation, represent with following formula:

$c\left(k\right)=\underset{m=0}{\overset{N_{\mathrm{FFT}}-1}{\mathrm{\&Sigma;}}}{s}^{*}(k+m)r(k+m+N_{\mathrm{FFT}}),k={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H06183217920060601E000032.png,H06183217920060601E000041.png"\; state="\{\{state\}\}">k</figure-callout>}}_1,\&CenterDot;\&CenterDot;\&CenterDot;,k_n$

Wherein, the targeting sequencing of s (k) for sending, N _FFTSize for the OFDM symbol.

Wherein, the described signal post-processing of step (7) is represented with following formula:

[Time_offset+N _cp/2：Time_offset+N _FFT-1，Time_offset：Time_offset+N _cp/2-1]

Wherein, Time_offset is the size that the estimated value of actual time delay adds the half cycles prefix, N _FFTBe the size of OFDM symbol, N _CpSize for Cyclic Prefix.

Of the present inventionly in the MIMO+OFDM communication system, realize synchronous method, owing to adopted the time one subsynchronous, frequency offset estimating, frequency offset estimating value to different antennae waits gain (ERC) to merge, utilize the frequency offset estimating value that newly obtains that the reception data of every antenna are carried out compensate of frequency deviation, the time of carrying out second synchronization, the antenna access time synchronous points the strongest according to received signal power, the scheme of select time second synchronization reprocessing, improved synchronization accuracy greatly, the received signal to noise ratio that can improve signal when satisfying the job requirement precision has promptly improved the performance of system, and do not expend too much system resource, can not increase the redundancy of system, operand is also very little, is beneficial to very much Project Realization.

Description of drawings

Fig. 1 is according to realizing synchronous method flow schematic diagram in the described MIMO+OFDM wireless system of the embodiment of the invention;

Fig. 2 is according to the schematic diagram of realizing a time method for synchronous in the synchronous method in the described MIMO+OFDM wireless system of the embodiment of the invention;

Fig. 3 is according to the schematic diagram of realizing frequency deviation estimating method in the synchronous method in the described MIMO+OFDM wireless system of the embodiment of the invention;

Fig. 4 is according to the schematic diagram of realizing time second synchronization method in the synchronous method in the described MIMO+OFDM wireless system of the embodiment of the invention;

Fig. 5 is the structural representation according to time-domain symbol in the described MIMO+OFDM wireless system of the embodiment of the invention;

Fig. 6 is the structural representation according to time synchronized point in the described MIMO+OFDM wireless system of the embodiment of the invention.

Embodiment

Below in conjunction with accompanying drawing, specific embodiments of the invention are carried out comparatively detailed explanation.

With reference to figure 1, for realizing synchronous method flow schematic diagram in the described MIMO+OFDM wireless system of the embodiment of the invention, detailed process is as follows:

Step 110: on every transmitting antenna, construct leading/synchronizing sequence and framing respectively and send.

Construct leading/synchronizing sequence during the transmitting terminal framing on every transmitting antenna, its preferred version comprises Cyclic Prefix and PN sequence, and targeting sequencing can comprise at least one leading symbol, and its temporal signatures is that length is N _IThe PN sequence repeat I=N/N wherein I time _I, N is the sub-carrier number of OFDM.The OFDM data symbol that should send on the every transmitting antenna respectively after the framing with every transmitting antenna of described structure on leading/synchronizing sequence framing after send simultaneously.

Step 120: in conjunction with CP information, it is subsynchronous to carry out time domain one on every reception antenna.

Described time domain one subsynchronous preferred version is for carrying out the relevant of significant character length based on the CP in the receiving terminal OFDM symbol, and correlated results carries out normalized to the correlated series energy, be time Synchronous Processing, can choose greater than 0.5 times of maximum and less than peaked any one number and be decision threshold, can obtain the set of optimal synchronisation point after subsynchronous, as shown in Figure 2.

Step 130: on every reception antenna, carry out the time domain frequency offset estimating respectively.

The described method preferred version that carries out frequency offset estimating based on targeting sequencing is first synchronous points of utilizing in the minor synchronous point set, thresholding slip conjugate multiplication when carrying out, utilize the frequency offset estimating value Freq_offset (i) on the maximum output acquisition i root reception antenna, as shown in Figure 3.

Step 140: the frequency offset estimating value Freq_offset (i) on the every reception antenna is carried out equal gain combining, obtain final averaged frequency offset estimated value $\stackrel{\&OverBar;}{\mathrm{Freq}\_\mathrm{Offset}}=(1/N_R)*\underset{i=1}{\overset{N_R}{\mathrm{\&Sigma;}}}\mathrm{Freq}\_\mathrm{Offset}\left(i\right),$ And use this result respectively the data on the every reception antenna to be carried out compensate of frequency deviation.

Step 150: utilize leading symbol to carry out the time second synchronization.

On every reception antenna, described time second synchronization is included in the synchronous points range of convergence of a subsynchronous output, and leading symbol that receives behind the compensate of frequency deviation and transmission leading symbol are carried out the time domain cross-correlation, obtains time second synchronization point, as shown in Figure 4.

Step 160: select best time second synchronization point.

Correlation peak to all reception antennas is made comparisons, and the time synchronized point of choosing main peak value and that root antenna of the ratio maximum of minor peaks is as Best Times second synchronization point.

Step 170: utilize described Best Times second synchronization point, carry out synchronous reprocessing.Utilize the special construction of time second synchronization point and OFDM to adjust output sequence, as shown in Figure 5.

In the above step, can be on every antenna separate processes, carry out time synchronized and Frequency Synchronization and reprocessing synchronously respectively; Also the result on the every antenna can be waited gain or high specific to merge, especially for the estimation of frequency deviation value.

Wherein, in the synchronous method of described realization, described leading/synchronizing sequence comprises two parts: one is described Cyclic Prefix; The 2nd, the leading symbol that constitutes by the identical PN sequence of length, its length all is integral multiple/one of efficient orthogonal frequency division multiplexing data length, can be 1/2,1/4 or other value, for the integer frequency offset of the generation that guarantees ofdm system can not surpass estimation range, according to the number of times that repeats on the actual conditions design short preamble symbols time domain, this leading symbol on the different transmitting antennas can be the same, if be used for channel estimating, must guarantee quadrature.Utilize leading symbol to carry out synchronously in the synchronous method of described realization, its output synchronously obtains a set that comprises best synchronous points, and relevant extreme value output back half choose synchronous points when promptly not having the OFDM symbol inter-block-interference, need to utilize the characteristic of OFDM Cyclic Prefix to carry out reprocessing after synchronous points is chosen.

Wherein, as described in step 110, the design of preamble structure as shown in Figure 6, number of sub carrier wave is 256.The k time sampling of received signal is output as r (k), is made of signal and receiver noise through channel.Sampled signal is cushioned, and buffer length is carried out relevant treatment to obtain time synchronizing information with symbol lengths of buffering signals time-delay then greater than an OFDM symbol.

Wherein, as described in step 120, with reference to figure 2, for realizing the schematic diagram of a time method for synchronous in the synchronous method in the described MIMO+OFDM wireless system of the embodiment of the invention.Detailed process is as follows:

Step 210: sampled signal is cushioned, obtain buffering signals;

Step 220: buffering signals is carried out the N point postpone, be an effective OFDM symbol time time of delay, if corresponding sample frequency is the N gall nut carrier spacing, the delay sampling number is N so, otherwise will change;

Step 230: buffering signals and be delayed the signal that N order and arrived correlator by synchronous transport, carry out following operation:

$b\left(k\right)=\underset{m=0}{\overset{P-1}{\mathrm{\&Sigma;}}}r(m+k)r^{*}(m+k+N)$ Formula (1)

Wherein, P represents the length of CP symbol, and r is a receiving sequence.In k dropped on the length range of CP symbol constantly, this relevant output was very big, otherwise output is very little, and relevant peaks length is about the length of CP symbol.Above-mentioned relevant output can through type (2) iteration realize:

B (k+1)=b (k)-r (k) r ^*(k+N)+r (P+k) r ^*(P+k+N) formula (2)

Formula has reduced the related operation amount as can be known thus.

The output of described correlator is to the signal power normalization in the correlation time length, utilize normalization output and realize the time synchronized judgement via checkout gear, detection threshold is provided by system, this synchronous error is bigger, particularly under the Complex Channel situation, and because correlation length is limited, can not make full use of the power of whole symbol, therefore relevant affected by noise bigger.

Be not used for realizing synchronization decisions during present embodiment time domain one is subsynchronous, but possible synchronous points (point that correlation peak is bigger) position is designated as { k ₁, k ₂..., k _nAs output, and via the time domain second synchronization of slip correlation preamble sequence finish final synchronously.

Wherein, as described in step 130, with reference to figure 3, for realizing the schematic diagram of frequency deviation estimating method in the synchronous method in the described MIMO+OFDM wireless system of the embodiment of the invention.Detailed process is as follows:

Step 310: the sequence buffering to after subsynchronous is sampled, and obtains sampled data r (k);

Step 320: the sampled data r (k) of a subsynchronous postorder row buffering is postponed N sampled point backward;

Step 330: in a sliding window, carry out point-to-point time domain conjugate point and multiply each other, ask relevant according to formula (3) then:

$z=\underset{n=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{r}_n{r}^{*}(n+N_S)=\underset{n=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{S}_n{e}^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H06183217920060601E000032.png,H06183217920060601E000041.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{f}_{\mathrm{\&Delta;}}n{T}_S}{S}^{*}(n+N_S)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H06183217920060601E000032.png,H06183217920060601E000041.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{f}_{\mathrm{\&Delta;}}(n+N_S)T_S}$

Formula (3)

$=e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H06183217920060601E000032.png,H06183217920060601E000041.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{f}_{\mathrm{\&Delta;}}{N}_S{T}_S}\underset{n=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\left|S_n\right|}^2$

Wherein, r is the targeting sequencing after subsynchronous through that receives, $S_n=r_n{e}^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H06183217920060601E000032.png,H06183217920060601E000041.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{f}_{\mathrm{\&Delta;}}n{T}_S},$ T _SBe OFDM symbol period, N _SRepresent leading/the length of repetitive sequence on time domain that synchronizing sequence adopted, L one satisfies the size of set of the optimal synchronisation point of decision threshold after subsynchronous.

Step 340: correlated results is carried out normalized, and wherein, described normalization is meant carries out normalization on the amplitude to the value of obtaining of correlator, obtains the peak value after relevant.Shown in the accompanying drawing 3, estimated value/(2 π/N) are meant the normalization of carrying out the frequency offset estimating value.

Step 350: estimate output frequency offset estimating value by (4) formula:

${\hat{f}}_{\mathrm{\&Delta;}}=\frac{\mathrm{angle}\left(z\right)}{2\mathrm{\&pi;}{N}_S{T}_S}$ Formula (4)

If obvious M _S=4, N _S=64, then the scope of frequency offset estimating is [2,2].Wherein, N _SRepresent leading/the length of repetitive sequence on time domain that synchronizing sequence adopted, M _SThe number of times that the expression repetitive sequence repeats.

Wherein, as described in step 140, the wait gain or the high specific of frequency offset estimating value merges on the different reception antennas, considers complexity, adopts equal gain combining in the present embodiment, as follows formula:

$\stackrel{\&OverBar;}{\mathrm{Freq}\_\mathrm{Offset}}=(1/N_R)*\underset{i=1}{\overset{N_R}{\mathrm{\&Sigma;}}}\mathrm{Freq}\_\mathrm{Offset}\left(i\right)$ Formula (5)

Wherein, N _RBe the reception antenna number, Freq_Offset (i) is the frequency offset estimating value of i root reception antenna.

Wherein, as described in step 150, with reference to figure 4, for realizing the schematic diagram of time domain second synchronization method in the synchronous method in the described MIMO+OFDM wireless system of embodiment, carry out on every reception antenna, detailed process is as follows:

Step 510: the sequence buffering is sampled, obtain sampled data r (k);

Step 520: with possible synchronous points set { k ₁, k ₂..., k _nAnd the buffering sampled data r (k) be input to cross-correlator, carry out operation suc as formula (5):

$c\left(k\right)=\underset{m=0}{\overset{N_{\mathrm{FFT}}-1}{\mathrm{\&Sigma;}}}{s}^{*}(k+m)r(k+m+N_{\mathrm{FFT}}),k={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H06183217920060601E000032.png,H06183217920060601E000041.png"\; state="\{\{state\}\}">k</figure-callout>}}_1,\&CenterDot;\&CenterDot;\&CenterDot;,k_n$ Formula (6)

Wherein, the targeting sequencing of s (k) for sending, N _FFTBe the size of OFDM symbol, the pilot frequency sequence of r (k) for carrying out receiving behind the frequency offset correction.Obviously, the correlated process of formula (6) can not realize with iteration, but its computing is only for gathering { k at a minor synchronous point ₁, k ₂..., k _nCarry out in the scope, so its operand is not very big.Simultaneously, because the time sampling sequence of received signal has experienced identical decline, therefore described time domain second synchronization is when accurate synchronous points, when formula (6) homophase addition, relevant peaks is more sharp-pointed, and maximum of points is a synchronous points, be subjected to the influence of long time delay for fear of received signal, cause synchronous points inaccurate, can get maximum of points CP length is got surplus method, to improve synchronous reliability.

Step 530: carry out synchronization decisions, export accurate synchronous points.

Make full use of leading structural design, make that the sync correlation peak output of this method is quite sharp-pointed, help synchronization decisions.Simultaneously, owing to utilized the signal energy of whole symbol, it is good therefore to work under little state of signal-to-noise.

Wherein, as described in step 170, be the structural representation of time synchronized point in the described MIMO+OFDM wireless system of the embodiment of the invention.

After the time second synchronization, general method of operation gets final product for directly removing CP.But this does not well utilize the characteristic of OFDM Cyclic Prefix, if utilize this characteristic, reduces the skew that synchronization delayed time causes, and improves the performance of receiver.Time_offset is the size that the estimated value of actual time delay adds half CP, actual consider to be this value characteristics that can utilize Cyclic Prefix can guaranteeing can not cause intersymbol interference, but well do not utilize the time delay estimated value well to reduce skew Effect on Performance.Therefore should take following post-processing approach after the time second synchronization, and then remove CP:

[Time_offset+N _Cp/ 2:Time_offset+N _FFT-1, Time_offset:Time_offset+N _Cp/ 2-1] formula (7)

In real system, two kinds of situations are arranged: the one, the frequency stability of working as transceiver is very high, and consider that the frequency deviation of this moment only was (to being a decimal after the subcarrier spacing normalization) of little several times when Doppler influenced the back frequency deviation value still less than the ofdm system subcarrier spacing.Frequency offset estimating only need be carried out fractional part of frequency offset and be estimated to get final product.

The 2nd, when the frequency stability of transceiver is not high, and consider when Doppler influences its value of back much larger than the ofdm system subcarrier spacing that in fact frequency deviation not only comprises little several times, but also comprises several integral multiples (being the integral multiple of subcarrier spacing).At this moment, leading symbol need be configured to shorter leading symbol, can enlarge frequency offset estimation range.

The maximum Doppler of the frequency stability of system's transceiver, system's support and subcarrier spacing are known, therefore be easy to learn that according to different system parameters designs frequency offset estimating is first kind of situation or second kind, carry out different processing according to different situations.

Above described method, it is Synchronous Processing at many antennas, many reception antennas synchronously all be based on the processing method of an antenna, roughly can be divided into three kinds of processing modes: can be on every antenna separate processes, carry out time synchronized and Frequency Synchronization and reprocessing synchronously respectively; Also the result on the every antenna can be waited gain or high specific to merge especially frequency offset estimating part, deal with again; The simplest method is only wherein a strongest antenna of received signal power to be carried out one subsynchronous, frequency offset estimating of time, time second synchronization, gets final product in the enterprising line frequency offset compensation of each root antenna, reprocessing synchronously respectively.Concrete condition will be chosen according to the design of real system.

Can be drawn by the above, whole M IMO+OFDM synchronizing process is divided into following step: be the every leading and framing emission of transmitting antenna structure; Every reception antenna carry out in conjunction with the time one of CP subsynchronous; Utilize targeting sequencing to carry out estimating partially at the every enterprising line frequency of reception antenna; Utilize equal gain combining to obtain final averaged frequency offset estimated value, and carry out compensate of frequency deviation respectively; Utilize leading symbol to carry out the time domain cross-correlation respectively at every reception antenna, obtain time domain second synchronization point; According to the ratio of main peak value and minor peaks, choose best time synchronized point; Carry out synchronous reprocessing.

The CP information of the subsynchronous OFDM of utilization of time one provides possible synchronous points scope for the time domain second synchronization, and the frequency offset estimating part is carried out compensate of frequency deviation for the time second synchronization, utilizes equal gain combining, can improve the precision of frequency offset estimating; Time domain second synchronization part obtains synchronizing information at the designed leading relevant treatment of carrying out, and according to the ratio of main peak value and minor peaks, chooses best time synchronized point, carries out synchronous reprocessing in conjunction with synchronous points, maximum possible obtain preferable received signal.

The method for synchronous of a kind of radio MIMO+ofdm system disclosed in this invention with traditional based on CP synchronously, compare based on the method for a plurality of leading symbols and multi-dimensional search and to have following characteristics: only need a leading symbol can realize the time synchronized of OFDM, for the system resource that time synchronized expends smaller; The realization synchronization accuracy is higher, its relevant peaks in the output of time domain second synchronization is quite sharp-pointed, output around maximum is all very little, be easy to adjudicate, and since time one subsynchronously the synchronous points scope is estimated, therefore time domain second synchronization operand is little, and can take synchronous reprocessing to improve the performance of system; Can be only realize in a big way frequency offset estimating with a short preamble symbols, this is based on, and method such as CP can't accomplish, and the Frequency Synchronization operand is very little, utilizes the frequency deviation result of many antennas to merge processing, can reduce the error of frequency offset estimating; After the time second synchronization, the time synchronized reprocessing of carrying out does not increase operand, is equal to the original CP that goes substantially and handles, and has still reduced the skew of phase place, has improved the amplitude of received signal.

But should be understood that above-mentioned description at preferred embodiment of the present invention is comparatively concrete, can not therefore think the restriction to scope of patent protection of the present invention, scope of patent protection of the present invention should be as the criterion with claims.

Claims (11)

1. a method for realizing synchronization in a MIMO system, is characterized in that, comprises the steps: (1) The transmitting end constructs a preamble/synchronization sequence, respectively frames the OFDM data symbols on different transmission antennas and the preamble/synchronization sequence on each of the constructed transmission antennas and transmits them simultaneously; (2) Based on multiple receiving antennas, the cyclic prefix in the OFDM symbol is used to correlate the effective symbol length, and the correlation result is processed once in the time domain for the correlation sequence energy to obtain the best synchronization after one synchronization collection of points; (3) Time-domain frequency offset estimation is performed based on the preamble/synchronization sequence based on the primary time synchronization point obtained by each receiving antenna; (4) The results of time-domain frequency offset estimates obtained on each receiving antenna are jointly combined with equal gains to obtain a final average frequency offset estimate, and the results are used to perform frequency analysis on the data on each receiving antenna. partial compensation; (5) On each receiving antenna, within the set range of the synchronization point of a synchronization output, the preamble symbols obtained by the receiving end after frequency offset compensation and the transmitted preamble symbols are cross-correlated in the time domain, and the maximum value is used to compare the cyclic Take the remainder of the prefix length to get the second time synchronization point; (6) compare the correlation peaks of all receiving antennas, and select the time synchronization point of the antenna with the largest peak value/secondary peak value as the best time secondary synchronization point; (7) After finding the optimal time secondary synchronization point, for the received data of each transmitting antenna, the time-domain circular convolution characteristic of OFDM is used to carry out the signal post-processing after precise synchronization. 2. The method according to claim 1, characterized in that the preamble/synchronization sequence in step (1) must be constructed on each transmit antenna at the sending end, including a cyclic prefix and a PN sequence, and the preamble sequence includes a synchronous/preamble symbol. 3. The method according to claim 2, wherein the preamble symbols are composed of repeated PN sequences with the same length. 4. The method according to claim 2 or 3, wherein the length of the PN sequence is one integer multiple of the effective OFDM data length. 5. the method for claim 1 is characterized in that, the correlation of effective symbol length described in step (2) is represented by following formula: $\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; r</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>$ Among them, P represents the length of the cyclic prefix symbol, r is the received sequence, and N is the number of delayed samples. 6. The method as claimed in claim 1, characterized in that, the time domain primary processing described in step (2) is to do the same processing on each receiving antenna, and select any value greater than half of the maximum value and less than the maximum value. A number is used as the decision threshold. 7. The method according to claim 1, characterized in that, said step (3) comprises, corresponding to each receiving antenna, utilizing the first synchronization point in the time primary synchronization point set to perform time-domain value sliding synchronization Yoke multiplication, the frequency offset estimation of the available preamble symbols, the estimation range is [-N/2, N/2], where N is the number of times the preamble symbols are repeated in the time domain, and is performed according to the actual frequency offset select. 8. The method according to claim 7, wherein the frequency offset estimation is represented by the following formula: ${\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}}_{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; the\; angle</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}}$ Among them, T _S is the OFDM symbol period, N _S represents the length of the repeated sequence used in the preamble/synchronization sequence in the time domain, and z is expressed by the following formula: $\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}}\mathrm{<span\; class="notranslate">\; no</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}}{\mathrm{<span\; class="notranslate">\; S</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}}$ $<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}}\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}$ Among them, r is the preamble sequence received after one synchronization,

T _S is the OFDM symbol period, and L is the size of the best synchronization point set that satisfies the decision threshold after one synchronization. 9. method as claimed in claim 1, is characterized in that, equal gain described in step (4) combines with following formula expression: $\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; Freq</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; Offset</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; *</span>}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\mathrm{<span\; class="notranslate">\; Freq</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; Offset</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>$ Wherein, _NR is the number of receiving antennas, and Freq_Offset(i) is an estimated frequency offset value of the i-th receiving antenna. 10. The method according to claim 1, characterized in that, the preamble symbols obtained by the receiving end after frequency offset compensation and the preamble symbols sent in step (5) are carried out in time domain cross-correlation, represented by the following formula: $\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; FFT</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; FFT</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}$ Wherein, s(k) is the transmitted preamble sequence, _{and NFFT} is the size of the OFDM symbol. 11. The method according to claim 1, characterized in that the signal post-processing described in step (7) is represented by the following formula: [Time_offset+N _cp /2: Time_offset+N _FFT -1, Time_offset: Time_offset+N _cp /2-1] Wherein, Time_offset is the estimated value of the actual time delay plus half the size of the cyclic prefix, _NFFT is the size of the OFDM symbol, and N _cp is the size of the cyclic prefix.

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