CN1306745C - Guiding plan based on time frequency synchronous training sequence - Google Patents

Abstract

The present invention discloses a guiding project on the basis of a time and frequency synchronous training sequence, which utilizes the favorable periodic correlation characteristics and the constant amplitude characteristics of a CAZAC sequence to use the CAZAC sequence as a known measuring sequence and extract a part of the CAZAC sequence as a guiding signal so as to properly amplify the power of the guiding signal, and moreover, the corresponding position of a data signal, which is embedded with the guiding signal, is set to zero. The known measuring sequence can be used for not only the synchronization of time and frequency, but also channel estimation; a system can obtain the more accurate channel estimation and the more high performance of data demodulation by using the project of the present invention so as to cause the system to more exactly track the fading variation of channels in time.

Description

A kind of guidance method based on the temporal frequency synchronous training sequence

Technical field

The invention belongs to communication technical field, particularly the channel estimation methods of assisting based on time, frequency synchronization method and the guide symbol of training sequence in the communication technology.

Background technology

OFDM is called for short OFDM, owing to have the message transmission rate height, 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: ADSL (Asymmetric DigitalSubscriber Line), Wireless LAN is 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 have good anti-multipath, cochannel interference and impact noise ability and 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; LickhoSong; Hong Gil Kim; Taejoo Chang; Hyung Myung Kim, " Performance analysis of a coded OFDM system intime-varying multipath Rayleigh fading channels, " Vehicular Technology, IEEE Transactions on, Volume:48 Issue:5, Sept.1999, Page (s): 1610-1615 is described.

In ofdm system, time, Frequency Synchronization are the technology of a key, 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), and content sees document van de Beek, J.J. for details; Sandell, M.; Borjesson, P.O., " ML estimation of time and frequency offset in OFDM systems; " Signal Processing, IEEETransactions on, Volume:45 Issue:7, July 1997, Page (s): 1800-1805.One of simultaneous techniques of OFDM is to utilize known training sequence, training sequence is superimposed upon on the OFDM useful data making a start, and the correlation that the training sequence of receiving end utilization emission and receiving terminal have the training sequence signal is carried out time synchronized.Referring to document Tufvesson, F.; Edfors, O.; Faulkner, M., " Time and frequency synchronization for OFDM using PN-sequence preambles; " Vehicular TechnologyConference, 1999.VTC 1999-Fall.IEEE VTS 50th, Volume:4,1999, Page (s): 2203-2207.Adopting the advantage of training sequence is not need extra system bandwidth, and the efficient that sends signal is higher.

Simultaneously, channel estimation technique is widely used in communication technical field, and whether channel estimating accurately is related to the performance of whole communication system.Because in actual environment, wireless channel is constantly changing, blind Detecting in the conventional estimated method and blind estimation can not estimate the conversion of channel timely, yet utilize known training sequence deadline, Frequency Synchronization accurately, utilize the auxiliary channel estimating of guide symbol that from known training sequence, obtains simultaneously, can accurately follow the tracks of the real-time change of channel, and then estimate the decline of channel, carry out necessary compensation to received signal at receiving terminal then, improve the performance of whole system with this.Content sees for details: J.K.Cavers, " An analysis of pilot symbol assistedmodulation for Rayleigh fading channels, " IEEE Trans.Veh.Technol., vol.40, no.4, pp.686-693, Nov.1991.

The realization of the channel estimation technique that guide symbol is auxiliary need be inserted guide symbol in the data-signal that is sending of making a start, the design problem of promptly guiding pattern is the key of the auxiliary channel estimating of whole steering signal, and existing guiding pattern design criterion mainly contains:

(1) frequency domain sweep type pattern: guide symbol spreads all over whole frequency axis, promptly be separated by certain symbol lengths guiding OFDM symbol on place guide symbol fully, shown in figure (1), content sees for details: M.J.Fernandez-GetinoGarcia, S.Zazo and J.M.Paez-Borrallo, " Efficient Pilot Pattern Channel EstimationIn OFDM Systems Over HF Channels ", IEEE VTC ' 99, pp2193-2197.

(2) rectangular patterns: the positional alignment of guide symbol in time domain-frequency domain sample figure is rectangular, shown in figure (2), transverse axis express time axle wherein, the longitudinal axis is represented frequency axis, detailed content is seen: M.J.Fernandez-Getino Garcia, S.Zazo and J.M.Paez-Borrallo, " Pilot pattern for channel estimation estimation inOFDM " ELECTRONICS LETTERS 8 ^ThJune 2000 Vol.36 No.12, pp1049-1050.

(3) hexagon pattern: the positional alignment of guide symbol in time domain-frequency domain sample figure is hexagon, shown in figure (3), detailed content is seen: M.J.Fernandez-Getino Garcia, S.Zazo and J.M.Paez-Borrallo, " Pilot pattern for channel estimation estimation in OFDM " ELECTRONICSLETTERS 8 ^ThJune 2000 Vol.36 No.12, pp1049-1050.

Existing time based on training sequence, frequency synchronization method have its intrinsic limitation: when the relative energy (being about to total transmit signal energy normalization) of training sequence is excessive, will produce stronger interference to data-signal, make the desired data-signal that demodulates that receiving end can not be correct; When the energy of training sequence was low, the data-signal of transmission can produce strong interference to training sequence, and when receiving end was carried out simultaneous operation, the correlation of training sequence will be received destruction, and it is synchronous to carry out temporal frequency accurately.

In like manner, time, frequency synchronization method based on training sequence are also influential to guidance method: training sequence not only can produce the data-signal that sends and disturb, and for the steering signal generation interference of inserting in the data-signal, cause the inaccuracy of receiving end channel estimating, thereby cause the decreased performance of whole OFDM system.

Summary of the invention

Task of the present invention provides a kind of guidance method based on the temporal frequency synchronous training sequence, promptly adopt method of the present invention, system can obtain channel estimating more accurately, and higher data demodulates performance, and the decline that the system that makes can follow the tracks of channel more accurately and timely changes.

The invention provides a kind of guidance method, it is characterized in that the following step (as shown in Figure 4) of its employing based on the temporal frequency synchronous training sequence:

Make a start:

Step 1 (determining training sequence) determines that the training sequence that adopts is that a kind of mould is constant, autocorrelation is zero permanent mould zero autocorrelation sequence, is called for short the CAZAC sequence, is expressed as z _kThe CAZAC sequence has the good period correlation properties, and the amplitude of sequence all remains constant in time domain and frequency domain, and we are the Chu sequence of N in the cycle of selecting for use in the explanation of this job step, wherein the value of N is 2 integral number power, and the production method of Chu sequence is as follows:

$c_n=e^{\frac{\mathrm{j\&pi;}}{N}{n}^2},0\&le;n<N;$

Step 2 (distribution power) CAZAC sequence z _kMultiply by the relative power factor ρ is the ratio of training sequence power and total power that transmits, $c_n^{\&prime;}=\sqrt{\mathrm{\&rho;}}\&CenterDot;c_n;$

Step 3 (FFT conversion) is carried out the Fourier transform that length is N with the CAZAC sequence, is called for short the FFT conversion:

$z_k=\frac{1}{\sqrt{N}}\underset{i=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{c}_i^{\&prime;}{e}^{-j\frac{2\mathrm{\&pi;ik}}{N}};$

Step 4 (extract guide symbol and amplify) is according to rectangle guiding pattern design criterion, and the CAZAC sequence after the FFT conversion is chosen the operation of guide symbol, determines pilot sequence p _{L, k}, wherein l is an OFDM symbol sequence number, k is the subcarrier sequence number, D _tBe the interval of guide symbol in time domain, D _fBe the interval of guide symbol on subcarrier, A _pBe the ratio of pilot power, that is: with total power that transmits

Step 5 (for data signal distribution power) multiply by the data power factor with data-signal

Step 6 (it is zero that the steering signal position is set) establishes zero according to above-mentioned steps 4 described guiding pattern design criterions to corresponding guide symbol position in the data-signal, establishes the data-signal of b (n) for sending, b _{L, k}For inserting null value signal afterwards, that is: according to rectangle guiding pattern

Step 7 (data and training sequence addition, summation, and transmission) superposes x with the sequence of step 4 and step 6 generation _{L, k}=p _{L, k}+ b _{L, k}, obtain and signal x _{L, k}, then with x _{L, k}Send into the inverse Fourier transform module, be called for short the IFFT module, carry out inverse Fourier transform, obtain sending signal X _{L, n}, that is:

$X_{l,n}=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{x}_{l,k}{e}^{\frac{j2\mathrm{\&pi;nk}}{N}}.$

Receiving end:

It is synchronous 15 that step 8 is carried out temporal frequency in receiving end, removes protection time slot 16 then, carries out FFT conversion 9, extracts guide symbol again and carry out channel estimating 17, according to channel estimation results data carried out demodulation 19.

Just can realize later the purpose of the guidance method that the present invention is new through aforesaid operations.

Need to prove that the CAZAC sequence can be the Chu sequence of our usefulness in the above-mentioned steps, the CAZAC sequence can be Milewski sequence, Frank-Zadoff sequence or other known CAZAC sequences; The Milewski sequence is the Milwaukee sequence, and the Frank-Zadoff sequence is Frank-Zha Duofu sequence.The selection of guiding pattern can be a rectangle, can also be just hexagonal, and perhaps other known guiding patterns do not influence the generality of this patent.

Essence of the present invention is to extract guide symbol from the training sequence of transmitting terminal, and in the zero setting of the relevant position of data flow, then training sequence and data-signal is launched in the lump.Promptly when the known measurement sequence of utilization is carried out time, Frequency Synchronization, according to certain criterion therefrom the extracting part sub-sequence as guide symbol, and the power of amplification guide symbol, carry out channel estimating, and user data signal carries out channel estimating in the relevant position zero setting of inserting guide symbol exactly thereby reach.

From above-mentioned steps as can be seen, adopt guide symbol production method of the present invention, make steering signal can not be subjected to the influence of data-signal and training sequence, carry out channel estimating accurately in receiving end.So just can make fading compensation accurately to data, transmit information rapidly, reliably, improve the conformability of receiving terminal, reduce the hardware cost of receiving terminal in receiving end.

Innovation part of the present invention is to have made full use of CAZAC sequence good period correlation properties and normal amplitude characteristic, the CAZAC sequence is used as training sequence, and a kind of new guiding method for designing has been proposed: guide extraction on the basis of training sequence with the CAZAC sequence, suitably amplify pilot power, and in data-signal guiding relevant position zero setting, so fundamentally eliminated the interference of data-signal to steering signal, it because of steering signal again the part of training sequence itself, this has just guaranteed the purity of steering signal, having overcome in the prior art training sequence produces for the steering signal that inserts in the data-signal and disturbs, cause the inaccuracy of receiving end channel estimating, thereby cause the decreased performance of whole OFDM system, make receiving end can carry out channel estimating accurately; It is synchronous to use known training sequence both to be used for temporal frequency, is used for channel estimating again, and this has fully reduced overhead.

Description of drawings

Fig. 1 is the guiding pattern of frequency scanning type

Wherein, the grid of black is represented guide symbol, the grid designate data signal of white, and transverse axis express time axle, the longitudinal axis is represented frequency axis;

Fig. 2 is the rectangular arrangement figure of guide symbol

The hexagon-shaped configuration figure of Fig. 3 guide symbol

Fig. 4 is the implementation step block diagram of present specification

Among the figure, the CAZAC sequence is the Chu sequence, Be the relative power factor, FFT and IFFT computing length are N.

Fig. 5 is a transmitter fundamental diagram of the present invention

Wherein, the 1st, mapping block, the 2nd, data-signal power division module, the 3rd, zero insertion value module, the 4th, IFFT (contrary discrete Fourier transform (DFT)) module, the 5th, add protection time slot module, the 6th, the up-conversion module, the 7th, CAZAC sequence generation module, the 8th, training sequence power division module, the 9th, FFT (discrete Fourier transform (DFT)) module, the 10th, extract guiding module, the 11st, pilot power distribution module, the 12nd, the Multiplexing module of two paths of signals;

Fig. 6 is an operation of receiver principle schematic of the present invention

Wherein, the 13rd, down conversion module, the 14th, synchronization module, the 15th, go to protect the time slot module, the 9th, FFT module, the 16th, channel estimation module, the 17th, channel estimating compensating module, the 18th, demodulation module.

Embodiment:

Below to provide a concrete OFDM configuration down, the performing step of this patent.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=4096, the protection gap length is N _g=512.Get ρ=0.5, the energy of expression training sequence accounts for 50% of the gross energy that transmits.A _p=2, the expression pilot power is 2 times of gross power of transmitting.The CAZAC sequence selection is to be the Chu sequence of N=4096 in the cycle, is designated as C[i], i ∈ [0,4095].The guiding pattern is selected rectangular arrangement for use, and data-signal adopts the BPSK modulation.

As shown in Figure 5, data source is at first shone upon through module 1, passes through module 2 and power factor then

Multiply each other, determine the power of the data-signal of transmission, follow according to rectangle guiding design of patterns is accurate and survey, promptly finish the function of module 3 in the null value of guiding position insertion accordingly; While is 4096 Chu sequence by module 7 generation length, the sequence that produces is by training sequence (CAZAC sequence) power division module 8, pass through the FFT conversion module 9 that N=4096 is ordered again, guide extraction according to the design criterion of rectangle guiding pattern by module 10 through the data after the FFT conversion, the guide symbol of extraction is through guide symbol power division module 11 and amplitude factor A _ρMultiply each other; realize the function that pilot power is amplified; the data-signal of guiding that the process power amplification is handled and untreated training sequence carries out data multiplex in module 12; after superposeing, data sequence after training sequence and the process module 3 sends into IFFT module 4; finish the multi-carrier modulation function; add the protection time slots by module 5 then, after up-conversion unit 6 launch.

As shown in Figure 6; receiving terminal is earlier through down conversion module 13; it is synchronous that process module 14 is carried out temporal frequency then; signal synchronously passes through the FFT conversion again through removing protection time slot module 15, extracts guiding out and carries out channel estimating; the output result of channel estimation module 16 got to grip altogether with initial data multiply each other; be the function that module 17 is finished channel estimating, data 16 demodulation that compensation is later, output at last through demodulation module.

Claims (2)

1, a kind of guidance method based on the temporal frequency synchronous training sequence is characterized in that the following step of its employing:

Make a start and comprise:

Step 1 determines that the training sequence that adopts is that a kind of mould is constant, autocorrelation is zero permanent mould zero autocorrelation sequence, is called for short the CAZAC sequence, is expressed as z _k, the CAZAC sequence has the good period correlation properties, and the amplitude of sequence all remains constant in time domain and frequency domain, and the cycle of selecting for use of the CAZAC sequence here is the Chu sequence of N, and wherein the value of N is 2 integral number power, and the production method of Chu sequence is as follows:

$c_n=e^{\frac{\mathrm{j\&pi;}}{N}{n}^2}$ 0≤n＜N；

Step 2CAZAC sequence z _kMultiply by the relative power factor ρ is the ratio of training sequence power and total power that transmits,

$c_n^{\&prime;}=\sqrt{\mathrm{\&rho;}}\&CenterDot;c_n;$

Step 3 is carried out the Fourier transform that length is N with the CAZAC sequence, is called for short the FFT conversion: $z_k=\frac{1}{\sqrt{N}}\underset{i=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{c}_i^{\&prime;}{e}^{-j\frac{2\mathrm{\&pi;lk}}{N}};$

Step 4 is according to rectangle guiding pattern design criterion, and the CAZAC sequence after the FFT conversion is chosen the operation of guide symbol, determines pilot sequence p _{L, k}, wherein l is the OFDM symbol sequence number, is called for short OFDM symbol sequence number, k is the subcarrier sequence number, D _lBe the interval of guide symbol in time domain, D _fBe the interval of guide symbol on subcarrier, A _pBe the ratio of pilot power, that is: with total power that transmits

Step 5 multiply by the data power factor with data-signal

Step 6 establishes zero according to above-mentioned steps 4 described guiding pattern design criterions to corresponding guide symbol position in the data-signal, establishes the data-signal of b (n) for sending, b _{L, k}For inserting null value signal afterwards, that is: according to rectangle guiding pattern

Step 7 superposes x with the sequence of step 4 and step 6 generation _{L, k}=p _{L, k}+ b _{L, k}, obtain and signal x _{L, k}, then with x _{L, k}Send into the inverse Fourier transform module, be called for short the IFFT module, carry out inverse Fourier transform, obtain sending signal X _{L, n}, that is:

$X_{l,n}=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{x}_{l,k}{e}^{\frac{j2\mathrm{\&pi;nk}}{N}};$

Receiving end comprises:

It is synchronous 15 that step 8 is carried out temporal frequency in receiving end, removes protection time slot 16 then, carries out FFT conversion 9, extracts guide symbol again and carry out channel estimating 17, according to channel estimation results data carried out demodulation 19.

2, a kind of guidance method according to claim 2 based on the temporal frequency synchronous training sequence, it is characterized in that described CAZAC sequence is Milewski sequence or Frank-Zadoff sequence, the Milewski sequence is the Milwaukee sequence, and the Frank-Zadoff sequence is Frank-Zha Duofu sequence.

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