CN1773977B - MIMO-OFDM carrier frequency synchronizing method based on pilot frequency design - Google Patents

Abstract

The invention discloses a Multi-Input Multi-output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM) carrier synchronous method based on pilot frequency design in a wireless communication, which is applied to an MIMO-OFDM system having M emitting antennas, N receiving antennas and Q subcarriers including the following steps: dividing the whole Q subcarriers into M sub-wavebands, each sub-waveband occupying N continuous sub-carriers which correspondingly assigned to each emitting antenna, only a transmitter M transferring pilot frequency symbols for each sub-waveband while at other transmitters the Sm being zero; at end of each Sm, leaving several sub-carriers as protection, namely not transferring information; at end of each Sm, setting 0 in equal interval on the pilot frequency symbols of subcarriers, using Nzero and Nguard respectively as 0 and protective sub-carrier number in the sub-wavebands as well as setting symbols on sub-carriers (m-1)Nband+n[z]((Nband-Nguard)/Nzero)-1 for m=1,2,...M and n[z]=1,2,...Nzero. The invention eliminates multi-antenna interference in the MIMO system to a maximum extent. The method of the invention improves the estimation performance of carrier frequency offset, remarkably improves the carrier synchronous performance of the system as well as has characters of simple implementation and the like.

Description

MIMO-OFDM carrier frequency Synchronizing method based on pilot design

Technical field

The present invention relates to wireless communication field, relate in particular in a kind of wireless communication system MIMO-OFDM (multiple-input and multiple-output, Multi-InputMulti-Output based on pilot design; OFDM, OrthogonalFrequencyDivisionMultiplexing) carrier frequency Synchronizing method.

Background technology

OFDM is a kind of multi-carrier modulation technology, transmitting terminal sends data-modulated to a plurality of mutually orthogonal subcarriers simultaneously, and each subcarrier all is the arrowband, has very strong anti-multipath decline ability, thereby can think that for each subcarrier, channel is a flat fading.In theory, as the OFDM technology of high-speed radiocommunication system core, as long as suitably select the bandwidth of each carrier wave and adopt suitable error correction coding, multipath fading can be eliminated fully to the influence of system.If therefore do not have the restriction of power and bandwidth, can realize any transmission rate with the OFDM technology.And other technology does not just possess this specific character, because when adopting other technology, when data rate is increased to a certain numerical value, the frequency selective fading meeting dominate of channel, this moment, to increase transmitting power in any case also of no avail, this just the OFDM technology be applicable to the reason of high-speed radio system.But from the practical application angle, capacity for further increase system, improve system transmissions speed, the system of use multi-carrier modulation technology need increase the quantity of carrier wave, and this method can cause the increase of system complexity, and the bandwidth of increase system, this system for limited bandwidth and power limited is obviously not really suitable.And ofdm system to exist synchronously (carrier wave, symbol and regularly synchronously) to require high, must control technical problems such as peak-to-average force ratio effectively, certainly, many solutions have been arranged at present, and have reached practical requirement.On the other hand, key technology as next generation wireless communication system (B3G/4G, WLAN, BWA, MBWA etc.), the MIMO technology has also obtained increasingly extensive concern and application, the MIMO technology can improve the capability of communication system and the availability of frequency spectrum exponentially under the situation that does not increase bandwidth, therefore the MIMO technology is combined with the OFDM technology, can adapt to the requirement of system development trend of future generation well.Studies show that under the fading channel environment, ofdm system is fit to use the MIMO technology to come the raising capacity very much.The MIMO-OFDM technology is by adopting array antenna implementation space diversity in the OFDM transmission system, improved signal quality, is joint OFDM and MIMO and a kind of new technology of obtaining.It has utilized time, three kinds of diversity techniques of frequency and space, and wireless system is increased greatly to the tolerance limit of noise, interference, multipath.But the applied environment of its hypothesis is the flat fading wireless channel, and this hypothesis often is present in the narrow-band communication system, generally is invalid in wide-band communication system.

Prior art is based on the OFDM carrier frequency frequency deviation estimating method of pilot tone basically, and a class is to use at simple OFDM technology, as

" Blindhigh-resolutionuplinksynchronizationofOFDM-basedmul tipleaccessschemes; " (H.Bolcskei, 1999, Proc.IEEEWorkshopSignalProcessingAdvancesinWireles sCommun., Annapolis, MD, pp.166-169), " CarrierfrequencyoffsetacquisitionandtrackingforOFDMsyste ms " (M.LuiseandR.Reggiannini, 1996, IEEETrans.Commun., vol.44, pp.1590-1598, Nov.), " AnimprovedfrequencyoffsetestimatorforOFDMapplications " (M.MorelliandU.Mengali, 1999, IEEECommun.Lett., vol.3, pp.75-77, Mar.), " RobustfrequencyandtimingsynchronizationforOFDM " (T.M.SchmidlandD.C.Cox, 1997, IEEETrans.Commun., vol.45, pp.1613-1621 is Dec.) with " AhighefficiencycarrierestimatorforOFDMcommunications " (H.LiuandU.Tureli, 1998, IEEECommun.Lett., vol.2, pp.104-106, Apr.) described technology, but above-mentioned technology is at pure ofdm system all, therefore be not suitable under the MIMO-OFDM system synchronously.Another kind of is to use about the technology of OFDM under the MIMO situation, as " OFDMblindcarrieroffsetestimation:ESPRIT; " (U.Tureli, H.Liuand M.D.Zoltowski, 2000, IEEETrans.Commun., vol.48, pp.1459-1461, Sep.), these methods are not considered the complexity of mimo system, thereby also inapplicable under actual conditions.In the prior art, pilot frequency locations is normally fixing, and 0 pilot tone usually is to arrange continuously, be unfavorable for many antenna interference (MAI, elimination Multi-Antenna-Interference), thereby influence the carrier frequency estimated performance.

Summary of the invention

Technical problem to be solved by this invention provides a kind of MIMO-OFDM carrier frequency Synchronizing method based on pilot design, realizes that to overcome the system that prior art exists complicated, MAI eliminates shortcomings such as ability.

MIMO-OFDM carrier frequency Synchronizing method based on pilot design of the present invention is applied to have M transmitting antenna, the MIMO-OFDM system of an a N reception antenna and Q carrier frequency, may further comprise the steps:

(1) whole Q sub-carrier frequency is divided into M sub-band, each sub-band accounts for

Individual continuous sub-carrier frequency, task each transmitting antenna corresponding the branch.Each sub-band S _mOnly from transmitter m transmitted pilot symbol, and be 0 at other transmitter;

(2) at each S _mThe end, residual sub-carrier frequency is as protection, the breath of promptly not delivering a letter;

(3) at each S _mIn, the frequency pilot sign on the sub-carrier frequency uniformly-spaced puts 0.N _ZeroAnd N _GuardBe respectively 0 sub-carrier frequency number and the sub-carrier frequency number of protection in the sub-band, at sub-carrier frequency

For m=1,2 ..., M and n _z=1,2 ..., N _ZeroLast set symbol; Wherein, N _Guard+ N _Zero＞L, L are the maximum of multidiameter;

For further improving performance, pilot frequency locations is carried out saltus step by following algorithm: to m transmitter, and m=1,2 ..., M, its transmission content is: when b=1, be sub-band S _mDivide and task m transmitter; B＞1 o'clock is if (m+b-1) mod M ≠ 0 is S _{(m+b) mod M}Otherwise, be S _M

MIMO-OFDM carrier frequency Synchronizing method based on pilot design of the present invention.At under MIMO and the situation that OFDM is used in combination, the characteristics that the Nonlinear Transformation in Frequency Offset Estimation of OFDM is more difficult than simple ofdm system, having provided a kind of carrier frequency position is provided with-the sub-band algorithm according to certain rules, thereby eliminate the MAI in the mimo system to greatest extent, improve the method for Nonlinear Transformation in Frequency Offset Estimation performance, system's carrier frequency synchronization performance is significantly improved.Simultaneously, the method for the invention has the characteristics such as simple that realize.

Description of drawings

Fig. 1 is the frame of reference block diagram of the method for the invention.

Fig. 2 is the method for the invention neutron wave band algorithm pilot distribution instance graph.

Distribution instance graph when Fig. 3 is the saltus step of the method for the invention neutron wave band algorithm pilot tone.

Embodiment

Below in conjunction with the drawings and specific embodiments the method for the invention is described further.

The present invention is directed to system shown in Figure 1, propose a kind of effective carrier position jump method, as shown in Figure 3.Compare with the method for not saltus step (promptly shown in Figure 2), can obtain more performance.

The applied system model of the present invention as shown in Figure 1, the MIMO-OFDM system has M transmitting antenna, a N reception antenna, Q sub-carrier frequency.At transmitting terminal, m sub antenna, b the data block that is launched symbol can be expressed as:

a _m，b＝[a _m，b(0)，a _m，b(1)，L，a _m，b(Q-1)] ^T (1)

Before the emission, finish the OFDM modulation, be expressed as by the IFFT computing that a Q is ordered:

$s_{m,b}\left(i\right)=\frac{1}{\sqrt{Q}}\underset{q=0}{\overset{Q-1}{\mathrm{\&Sigma;}}}{a}_{m,b}\left(q\right)e^{\frac{\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H04188877720041111E000012.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;qi}}{Q}},i=0,K,Q-1---\left(2\right)$

The ofdm signal of modulation is added CP and carries out up-conversion, then by quasi-static, a multipath wireless channel, receiving terminal through opposite down-conversion, remove CP after, the baseband signal that receives on n receiver is expressed as:

$r_{n,b}\left(i\right)=\frac{1}{\sqrt{Q}}\underset{q=0}{\overset{M}{\mathrm{\&Sigma;}}}\underset{q=0}{\overset{Q-1}{\mathrm{\&Sigma;}}}{h}_{m,n}\left(q\right)a_{m,b}\left(q\right){\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="H04188877720041111E000012.png"\; state="\{\{state\}\}">e</figure-callout>}}^{\frac{j}{}}+{\mathrm{\&eta;}}_{n,b}\left(i\right),i=0,K,Q-1---\left(3\right)$

Here, h _{M, n}(q) be transmitter m to the impulse response of receiver n when q the sub-carrier frequency.η _{N, b}(i) be additive white Gaussian noise (AWGN), average and variance be (0, σ ²).

Because factors such as transmitting-receiving frequency source difference, channel Doppler frequency shifts, the actual reception signal is:

$r_{n,b}^{\&prime;}\left(i\right)=\frac{1}{\sqrt{Q}}\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="H04188877720041111E000012.png"\; state="\{\{state\}\}">e</figure-callout>}}^j\underset{q=0}{\overset{Q-1}{\mathrm{\&Sigma;}}}{h}_{m,n}\left(q\right)a_{m,b}\left(q\right){\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="H04188877720041111E000012.png"\; state="\{\{state\}\}">e</figure-callout>}}^{\frac{j}{}}+{\mathrm{\&eta;}}_{n,b}\left(i\right)---\left(4\right)$

Here, Normalization frequency deviation from m transmitter to n receiver to subcarrier.The received signal of the individual subcarrier of q ' is:

$R_{n,b}^{\&prime;}\left(q^{\&prime;}\right)=\frac{1}{\sqrt{Q}}\underset{i=0}{\overset{Q-1}{\mathrm{\&Sigma;}}}\left[\underset{m=1}{\overset{\mathrm{<figure-callout\; id="2"\; label="M\; e\; j"\; filenames="H04188877720041111E000012.png"\; state="\{\{state\}\}">M</figure-callout>}}{\mathrm{\&Sigma;}}}{e}^j{2\mathrm{\&pi;}{f}_V^{(m,n)}(i+(b-1)(Q+K))}^{}\underset{q=0}{\overset{Q-1}{\mathrm{\&Sigma;}}}{h}_{m,n}\left(q\right)a_{m,b}\left(q\right){\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="H04188877720041111E000012.png"\; state="\{\{state\}\}">e</figure-callout>}}^j\right]+{\mathrm{\&xi;}}_{n,b}\left(q^{\&prime;}\right)---\left(5\right)$

$=\frac{1}{Q}\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="H04188877720041111E000012.png"\; state="\{\{state\}\}">e</figure-callout>}}^j{h}_{m,n}\left(q^{\&prime;}\right)a_{m,b}(q^{\&prime;}{)I}_{m,n}\left(f_V^{(m,n)}\right)$

$+\frac{1}{Q}\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="H04188877720041111E000012.png"\; state="\{\{state\}\}">e</figure-callout>}}^j\underset{q\&NotEqual;q^{\&prime;}}{\underset{q=0}{\overset{Q-1}{\mathrm{\&Sigma;}}}}{h}_{m,n}\left(q\right)a_{m,b}\left(q\right)I_{m,n}(f_V^{(m,n)}+q-q^{\&prime;})+{\mathrm{\&xi;}}_{n,b}\left(q^{\&prime;}\right)$

Wherein Also be the AWGN noise, average and variance be (0, σ ²).

Be to be dealt into the ICI coefficient of q subcarrier of n receipts to the individual sub-intercarrier of q ' from m:

$I_{m,n}(f_V^{(m,n)}+q-q^{\&prime;})=\frac{\sin \left(\mathrm{\&pi;}(f_V^{(m,n)}+q-q^{\&prime;})\right)}{Q\sin \left(\frac{\mathrm{\&pi;}}{Q}(f_V^{(m,n)}+q-q^{\&prime;})\right)}\&CenterDot;e^{\mathrm{j\&pi;}(1-\frac{1}{Q})(f_V^{(m,n)}+q-q^{\&prime;})}---\left(6\right)$

When not having frequency deviation, following formula is in q=q ' time maximum, and is 0 when q ≠ q '.But when having frequency deviation, because the influence of ICI, even still be not 0 during q ≠ q '.The present invention is exactly by the design appropriate pilot signal, estimates effectively

Under the MIMO situation, the estimation of carrier frequency frequency deviation becomes complicated.At first, because each is all different to the frequency deviation that transmits and receives antenna, thereby there is MAI:

${\mathrm{\&Gamma;}}_{m,n,b}^{\&prime;}\left(q^{\&prime;}\right)=\frac{1}{Q}\underset{m^{\&prime;}\&NotEqual;m}{\overset{M}{\underset{m^{\&prime;}=1}{\mathrm{\&Sigma;}}}}{e}^{\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H04188877720041111E000012.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{f}_V^{(m^{\&prime;},n)}(b-1)(Q+K)}\underset{q=0}{\overset{Q-1}{\mathrm{\&Sigma;}}}{h}_{m^{\&prime;},n}\left(q\right)a_{m^{\&prime;},b}\left(q\right)I_{m^{\&prime;},n}(f_V^{(m^{\&prime;},n)}+q-q^{\&prime;})---\left(7\right)$

In order to suppress MAI, at first whole frequency is divided into M sub-band, each transmitter only takies one of them subband in the transmission pilot signal, end at each sub-band keeps the experimental process carrier frequency, on this a little carrier frequency, do not transmit any signal, the setting of this sub-band can prove theoretically that not only it can suppress MAI effectively, also can be verified from simulation result.

At each sub-band, adopt and periodically in pilot tone, to insert O and replace continuity in [5] and fill out 0 method.The definition cost function:

$F_{m,n}\left({\hat{f}}_V^{(m,n)}\right)=\underset{q^{\&prime;}\&Element;Q_{z,m}}{\mathrm{\&Sigma;}}{\left|\right|{\hat{R}}_{n,b}^{\&prime;}\left(q^{\&prime;}\right)\left|\right|}^2---\left(8\right)$

Here, Q _{Z, m}Represent that the corresponding frequency pilot sign of m transmitter is 0 sub-carrier frequency sequence number.Simulation result shows, compares with continuous 0 method, and this method is more responsive to the variation of carrier frequency frequency deviation, thereby is more convenient for estimating the carrier frequency frequency deviation.

For the net synchronization capability of further improvement system, and consider that in real system not only need to estimate carrier wave frequency deviation, channel parameter also is the key that influences the whole system performance.On the basis of the above, with the pilot frequency locations saltus step according to certain rules that distributes, thereby make frequency offset estimating be no longer dependent in each sub-band 0 distribution, and can carry out the estimation of channel parameter effectively.

The present invention can be summarized as following step:

1, whole Q sub-carrier frequency is divided into M sub-band, each sub-band accounts for Individual continuous sub-carrier frequency, task each transmitting antenna corresponding the branch.Each sub-band S _mOnly from transmitter m transmitted pilot symbol, and be 0 at other transmitter;

2, at each S _mThe end, residual sub-carrier frequency is as protection, the breath of promptly not delivering a letter;

3, at each S _mIn, the frequency pilot sign on the sub-carrier frequency uniformly-spaced puts 0, N _ZeroAnd N _GuardBe respectively 0 sub-carrier frequency number and the sub-carrier frequency number of protection in the sub-band, at sub-carrier frequency

For m=1,2 ..., M and n _z=1,2 ..., N _ZeroLast set symbol; Wherein, N _Guard+ N _Zero＞L, L are the maximum of multidiameter;

For further improving performance, pilot frequency locations is carried out saltus step by following algorithm: to m transmitter, and m=1,2 ..., M, its transmission content is: when b=1, be sub-band S _mDivide and task m transmitter; B＞1 o'clock is if (m+b-1) mod M ≠ 0 is S _{(m+n) mod M}Otherwise, be S _M

Specific implementation method below in conjunction with accompanying drawing 2 and 3 pairs of sub-band algorithms of the present invention of accompanying drawing is described below:

1) number of whole sub-carrier frequency is 64, and transmitting antenna is 4, and 64 sub-carrier frequency are divided into 4 sections, and each section comprised 16 continuous sub-carrier frequency.In the transmission pilot signal, any one transmitting antenna is sub-band emission frequency pilot sign therein only, and at other sub-band transmission signals not.

2) at the end of each sub-band, keep 4 sub-carrier frequency, protect the information of not transmitting on the sub-carrier frequency at these.

3) in each sub-band, equally spaced with on 04 subcarriers that are placed on wherein.

4) be further to improve performance, the pairing sub-band of each antenna also changes along with different OFDM frequency pilot signs, for example when first OFDM symbol, and transmitting antenna 1 corresponding first sub-band; When second frequency pilot sign, transmitting antenna 1 is corresponding to second sub-band, and the rest may be inferred.

Claims (5)

1. MIMO-OFDM carrier frequency Synchronizing method based on pilot design is applied to have M transmitting antenna, the MIMO-OFDM system of a N reception antenna and Q sub-carrier frequency, it is characterized in that, may further comprise the steps:

(1) whole Q sub-carrier frequency is divided into M sub-band, each sub-band accounts for

Individual continuous sub-carrier frequency, task each transmitting antenna, each sub-band S corresponding the branch _mOnly from transmitter m transmitted pilot symbol, and be 0 at other transmitter;

(2) at each S _mThe end, residual sub-carrier frequency is as protection, the breath of promptly not delivering a letter;

(3) at each S _mIn, the frequency pilot sign on the sub-carrier frequency uniformly-spaced puts 0, N _ZeroAnd N _GuardBe respectively 0 sub-carrier frequency number and the sub-carrier frequency number of protection in the sub-band, at sub-carrier frequency

For m=1,2 ..., M and n _z=1,2 ..., N _ZeroLast set symbol.

2. the MIMO-OFDM carrier frequency Synchronizing method based on pilot design according to claim 1 is characterized in that, in step (3), and N _Guard+ N _Zero＞L, L are the maximum of multidiameter.

3. the MIMO-OFDM carrier frequency Synchronizing method based on pilot design according to claim 1 is characterized in that pilot frequency locations is carried out saltus step by following algorithm: to m transmitter, and m=1,2 ..., M, its transmission content is: when b=1, be sub-band S _mDivide and task m transmitter; B＞1 o'clock is if (m+b-1) mod M ≠ 0 then is S _{(m+b) mod M}Otherwise, be S _MWherein, b is the sequence number that is launched the symbol data piece.

4. the MIMO-OFDM carrier frequency Synchronizing method based on pilot design according to claim 1 is characterized in that, when Q=64, M=4,

The time, may further comprise the steps:

1) any one transmitting antenna band emission frequency pilot sign therein only, and at other sub-band transmission signals not;

2) at the end of each sub-band, keep 4 sub-carrier frequency, protect the information of not transmitting on the sub-carrier frequency at these;

3) in each sub-band, equally spaced O is placed on 4 subcarriers wherein.

5. the MIMO-OFDM carrier frequency Synchronizing method based on pilot design according to claim 4, it is characterized in that, the pairing sub-band of each antenna changes along with different OFDM frequency pilot signs, when first OFDM symbol, and transmitting antenna 1 corresponding first sub-band; When second frequency pilot sign, transmitting antenna 1 is corresponding to second sub-band, and the rest may be inferred.

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