CN1937606A - Uplink carrier frequency tracking method for multi user block transmission system - Google Patents

Abstract

The present invention provides a carrier frequency tracking method for the uplink of a multi-user block transmission system. Under the following conditions: a. after user u captures the carrier frequency offset, the remaining relative carrier frequency offset is controlled within 2%; b. Synchronization has been completed; the tracking method includes the following steps: (1) the system enters a normal tracking state, the base station backs up the received original multi-user uplink time-domain baseband signal for each user, and the base station uses the frequency offset estimated value to correct the deviation, and simultaneously selects Set the correction threshold δ ₁ needed to transmit back the estimated value of frequency offset; (2) According to the results of channel estimation and judgment in the current frame, the base station reconstructs the time-domain signal corresponding to the signal of user u without frequency offset, and calculates the frequency (3) Use steps (1) and (2) to rectify the deviation and estimate the frequency deviation. Based on signal reconstruction, the present invention can effectively suppress the slow drift of the carrier frequency, has low computational complexity, simple implementation, fast tracking speed, high precision, does not occupy additional spectrum resources, and improves transmission efficiency.

Description

The carrier frequency tracking method of multi user block transmission system up link

Technical field

The present invention relates to wideband digital communications method, belong to the broadband wireless communication technique field.

Background technology

The communication technology has obtained tremendous development since nearest decades, particularly nineteen nineties, people's daily life and development and national economy have been produced far-reaching influence.And the future communications technology is just developing towards the direction of broadband high-speed, therefore many wideband digital transmission technologys are subjected to paying close attention to widely, the single carrier of OFDM (hereinafter to be referred as OFDM:OrthogonalFrequency Division Multiplexing) and frequency domain equalization (hereinafter to be referred as SC-FDE:Single Carrierwith Frequency Domain Equalization) is exactly two kinds of wideband digital transmission technologys of being paid attention to by people, they all belong to the piecemeal transmission technology, and the degree that present OFDM is paid close attention to will be considerably beyond SC-FDE, and in multiple standards, become support technology, for example: the IEEE802.11a in the WLAN (wireless local area network) (WLAN:Wireless Local Area Network); IEEE802.16 in the wireless MAN (WMAN:Wireless Metropolitan Area Network); Various high-speed digital subscriber lines (xDSL:Digital Subscriber Line) in the cable data transmission all are based on the standard of OFDM technology.SC-FDE is not adopted by these standards, just is the physical layer transmission technology with the common suggestion of OFDM in IEEE802.16.

OFDM and SC-FDE belong to the piecemeal transmission technology, and the system that they constituted is called block transmission system.In mobile communication system, must adopt effective multiple access technique.The fundamental type of multiple access technique has frequency division multiple access FDMA (Frequency Division Multiple Access), time division multiple access TDMA (Time Division MultipleAccess) and code division multiple access CDMA (Code Division Multiple Access).FDMA and TDMA realize simple, but need leave boundary belt at frequency domain and time domain respectively, and efficient is low.CDMA is as a kind of multiple access technology, and its user capacity is significantly higher than TDMA and FDMA, but in up link (from the portable terminal to the base station), generally has serious multi-user interference.Though can adopt multiuser detection with the antagonism multi-user interference, realize complicated; Also there be the problem identical with common CDMA in CDMA multiple carrier (MC-CDMA).Carrier sense in WLAN (wireless local area network)/collision elimination technology inserts if be used for the multiple access of mobile communication, and efficient is very low.

OFDM OFDMA (Orthogonal Frequency DiVision Multiple Access), it is a kind of broadband wireless communications multiple access technology that received publicity in recent years, be a kind of multiple access technique, can be regarded as a kind of novel frequency division multiple access technology in essence based on OFDM.OFDMA is divided into a large amount of narrowband subchannels to whole bandwidth, and a user distributes one or several groups of subchannels, and each groups of subchannels comprises the subchannel of some.OFDMA realizes simple, availability of frequency spectrum height.In up link, no multi-user interference.The scheme that OFDMA sets up groups of subchannels generally has two kinds, a kind of is that the subchannel of adjacent some forms groups of subchannels, be block groups of subchannels, all subchannels that second kind of scheme is groups of subchannels are dispersed in the whole bandwidth according to certain interval, i.e. the pectination groups of subchannels.Also comprehensive these two schemes of subchannel promptly are randomly dispersed in the whole bandwidth in addition.Second kind of scheme, the first kind of scheme of comparing has advantage, especially in frequency selective fading channels.

Multi user block transmission system DFT-SOFDM (Discrete Fourier Transform-Spread OFDM) is a kind of new broadband wireless communications multiple access technology, is OFDMA and the combining of SC-FDE.In transmission ends, after the signal process discrete Fourier transform (DFT) (hereinafter to be referred as DFT:Discrete Fourier Transform) of user u, obtain its frequency-region signal, this frequency-region signal is placed on the subchannel of user u, carry out inverse discrete Fourier transform (hereinafter to be referred as IDFT:Inverse DiscreteFourier Transform) again and become time domain again, add the Cyclic Prefix transmission.Compare with OFDMA, DFT-SOFDM does not have serious PAPR problem, but DFT-SOFDM and OFDMA are high especially to synchronous required precision.For example DFT-SOFDM and OFDMA require to remain relative carrier wave frequency deviation and are controlled in 2% the scope, otherwise the performance of system can be subjected to very big influence.

Simultaneous techniques can be divided into regularly synchronous and carrier frequency synchronization.Carrier frequency synchronization generally is divided into following two steps: carrier frequency acquisition and carrier frequency tracking are called thick carrier frequency synchronization and thin carrier frequency synchronization again.Receiving terminal at first carries out carrier frequency acquisition, and carrier frequency is controlled in the small range, makes the system can operate as normal.In order to keep good synchronization performance, must carry out carrier frequency tracking.Carrier frequency tracking is the variation that thin carrier frequency synchronization is followed the tracks of carrier frequency offset, prevents its cumulative effect, guarantees the precision of carrier frequency synchronization.So receiver must be followed the tracks of the variation of carrier frequency offset.

When setting up groups of subchannels, the requirement of non-block scheme carrier synchronization is tighter than block scheme, especially in the carrier frequency acquisition stage, because big carrier synchronization error can cause serious multiple access to disturb, even makes the neighboring user cisco unity malfunction.In the carrier frequency tracking stage, it is little that different groups of subchannels are set up the scheme difference.

At present in the up link of the system of DFT-SOFDM and OFDMA, carrier frequency tracking is a difficult point, the main at present carrier synchronization method that adopts based on pilot tone, promptly in transmission course, insert the known symbol of some receiving terminals, receiving terminal utilizes these known symbols to carry out estimating carrier frequencies, these class methods are generally fairly simple, estimated accuracy depend on insertion oneself know the quantity of symbol, shortcoming is the efficient that has reduced system.

Summary of the invention

The present invention is directed to the problem that prior art exists, the carrier frequency tracking method of a kind of multi user block transmission system (as OFDMA, DFT-SOFDM) up link is provided, this method has the precision height, realizes characteristic of simple under the situation of the spectrum efficiency of sacrificial system not.

Owing to the present invention is to provide a kind of carrier frequency tracking method, there is under the situation of shake slowly or slowly drift method of the present invention can follow the tracks of this shake or drift in carrier frequency, make system held a good synchronous regime.Because it only is a high-precision carrier frequency tracking method, thus to make some hypothesis to its condition of work, suppose that user u passes through carrier wave frequency deviation and catches after, remain relative carrier wave frequency deviation and be controlled in 2%.These hypothesis can be with existing high-precision carrier frequency acquisition method or in conjunction with certain thin realization synchronously, this acquisition mode is physical presence, and the paper " a kind of new OFDM carrier frequency acquisition method " that for example is published on " electronic information journal " the 6th phase in 2004 just can satisfy this required precision.In addition, suppose regularly to finish synchronously.

Meeting the following conditions down: a user u remains relative carrier wave frequency deviation to be controlled in 2% after catching through carrier wave frequency deviation; B regularly finishes synchronously, and the carrier frequency tracking method of multi user block transmission system up link of the present invention may further comprise the steps:

(1) system enters normal tracking mode, the up time domain baseband signal of the original multi-user r=(r that the base station will receive ₀, r ₁..., r _N-1) be each user ID, the base station utilizes the frequency offset estimating value to rectify a deviation, and selected simultaneously passback frequency offset estimating is worth needed correction thresholding δ ₁

(2) result who estimates and adjudicate according to current frame channel, the corresponding time-domain signal that does not contain frequency deviation of the signal of base station reconfiguration and user u, and recover the time-domain signal that contains frequency deviation of user u according to the groups of subchannels of user u, according to the signal that contains frequency deviation and the reconstruction signal that recover, calculate the estimated value of frequency deviation;

(3) utilize step (1), (2) correction, estimate frequency deviation value, this estimated value is used for the correcting frequency deviation of next frame signal.

Below above step is elaborated:

At first the symbol that relates to is carried out following explanation:

N: the whole label of subchannel, O≤n≤N-1.In the block transmission system, communicating pair is divided into N subchannel to whole available band, and in the block transmission system of realizing based on FFT, n also is the label of frequency domain variable simultaneously.

M: the local label of subchannel is m subchannel label in the same groups of subchannels, claims that m is the local label in this groups of subchannels.

k _m: the local label of expression groups of subchannels is the whole label of the subchannel of m.

K _u: u user's channel group set, the set that it is made up of the whole label of all subchannels of u user.

In (1) step, system enters normal tracking mode, the up time domain baseband signal of the original multi-user r=(r that the base station will receive ₀, r ₁..., r _N-I) be each user ID, the base station utilizes the frequency offset estimating value to rectify a deviation, and selected simultaneously passback frequency offset estimating is worth needed correction thresholding δ ₁

The frequency offset estimating value of supposing present frame is

The base station utilizes this estimated value to carry out the time domain correction.Method for correcting error is divided into two kinds, feedback method for correcting error and local method for correcting error.If the correction thresholding is δ ₁, 3% relative frequency deviation for example.

The feedback method for correcting error is as follows.If

In order to reduce The noise, generally work as Several times appear continuously, for example 3 times the time, receiving terminal feeds back to it user u again, user u rectifies a deviation, for example can with phase-locked loop tranmitting frequency be finely tuned, also can correct with additive method with the frequency deviation value of receiving as the error signal that sends the vibrator phase-locked loop, after user u end is finished correcting frequency deviation, send a correction complement mark position.

Local method for correcting error is as follows.If

The base station utilizes formula $r_n^{\widehat{\mathrm{\&epsiv;}}}=r_n{e}^{\frac{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20061006925900131.png,A20061006925900141.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}\widehat{\mathrm{\&epsiv;}}(n+L)}{N}},$ N=0,1 ..., N-1 is to the up time domain baseband signal of the original multi-user r=(r that receives ₀, r ₁..., r _N-1) rectify a deviation, preserve the vector after rectifying a deviation $r^{\widehat{\mathrm{\&epsiv;}}}=({\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="A20061006925900141.png"\; state="\{\{state\}\}">r</figure-callout>}}_0^{\widehat{\mathrm{\&epsiv;}}},r_1^{\widehat{\mathrm{\&epsiv;}}},...,r_{N-1}^{\widehat{\mathrm{\&epsiv;}}}).$

(2) step, result according to current frame channel estimation and judgement, the corresponding time-domain signal that does not contain frequency deviation of the signal of base station reconfiguration and user u, and recover the time-domain signal that contains frequency deviation of user u according to the groups of subchannels of user u, according to the signal that contains frequency deviation and the reconstruction signal that recover, calculate the estimated value of frequency deviation.

To r correction processing, the signal that obtains is designated as according to (1) process that goes on foot description

Carry out N point FFT conversion, promptly

$Y=\mathrm{FFT}\left(r^{\widehat{\mathrm{\&epsiv;}}}\right)---\left(1\right)$

Obtain the frequency-region signal of user u by following formula:

$Y^u=(Y_{k_0},{\mathrm{<figure-callout\; id="1"\; label="Y\; k"\; filenames="A20061006925900131.png,A20061006925900141.png"\; state="\{\{state\}\}">Y</figure-callout>}}_{k_{}},...,Y_{k_{M-1}})=(Y_0^u,Y_1^u,...,Y_{M-1}^u)$

Because method of the present invention is applicable to OFDMA and two kinds of systems of DFT-SOFDM, this step is different for the decision method and the reconstruction signal method of two kinds of systems, now is illustrated respectively:

A) OFDMA system:

Obtain the frequency domain characteristic of user u up channel by channel estimating

(m=0,1 ..., M-1), then to Y _m ^u, (m=0,1 ..., M-1) carry out frequency domain equalization, balanced data according to the modulation system judgement of adopting, is obtained the Frame symbol after user u adjudicates

(m=0,1 ..., M-1), its bit error rate can be lower, for example less than 10 ^-1Even can arrive 10 ^-3Magnitude, wherein M is the number of subchannels of u user's groups of subchannels, this moment, judging process was eliminated most frequency deviations and The noise; During reconstruction signal, utilize

(m=0,1 ..., M-1), according to formula:

If n=k _m∈ K _u, n=0,1 ..., N-1; (2)

And it is right ${\tilde{Y}}^u=({\tilde{Y}}_0^u,{\tilde{Y}}_0^u,...,{\tilde{Y}}_{N-1}^u)$ Do N point IFFT conversion, reconstruct the time domain form of the received signal that does not contain frequency deviation

Promptly ${\tilde{y}}^u=\mathrm{IFFT}\left({\tilde{Y}}^u\right);$

B) DFT-SOFDM system:

Obtain the frequency domain characteristic of user u up channel by channel estimating (m=0,1 ..., M-1), then to Y _m ^u, (m=0,1 ..., M-1) carry out frequency domain equalization, balanced data is done M point IFFT conversion, again the modulation system of the data based employing behind the IFFT is adjudicated, obtain the Frame symbol after user u adjudicates (m=0,1 ..., M-1), its bit error rate can be lower, for example less than 10 ^-1Even can arrive 10 ^-3Magnitude, wherein M is the number of subchannels of u user's groups of subchannels, this moment, judging process was eliminated most frequency deviations and The noise; During reconstruction signal, will (m=0,1 ..., M-1) do M point FFT conversion, promptly ${\tilde{S}}^u=\mathrm{FFT}\left({\tilde{S}}^u\right),$ According to formula:

If n=k _m∈ K _u, n=0,1 ..., N-1; (2 ')

And it is right ${\tilde{Y}}^u=({\tilde{Y}}_0^u,{\tilde{Y}}_1^u,...,{\tilde{Y}}_{N-1}^u)$ Do N point IFFT conversion, reconstruct the time domain form of the received signal that does not contain frequency deviation Promptly ${\tilde{y}}^u=\mathrm{IFFT}\left({\tilde{Y}}^u\right).$

No matter being OFDMA or DFT-SOFDM system, all is according to following formula, the frequency domain information of the user u that obtains:

(3)

It is carried out N point IFFT conversion, recover the time domain form signal that contains frequency deviation of user u, promptly ${\hat{y}}^u=\mathrm{IFFT}\left({\hat{Y}}^u\right).$ Under the less situation of deviation ratio, recovery value is near actual value.

Because containing the recovery value of the received signal time domain form of inherent spurious frequency deviation all is complex vector located with the reconstruction value that does not contain frequency deviation, respectively their component is write as:

${\hat{y}}_n^u=x_n+{\mathrm{jy}}_n,n=\mathrm{0,1},...,N-1$

${\tilde{y}}_n^u=a_n+{\mathrm{jb}}_n,n=\mathrm{0,1},...,N-1$

By formula

${\widehat{\mathrm{\&epsiv;}}}_i=\frac{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="A20061006925900131.png,A20061006925900141.png"\; state="\{\{state\}\}">N</figure-callout>}}{2\mathrm{\&pi;}}\frac{\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}(n+L)(y_n{a}_n-x_n{b}_n)}{\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{(n+L)}^2(a_{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="A20061006925900131.png,A20061006925900141.png"\; state="\{\{state\}\}">n</figure-callout>}}^2+b_m^2)}---\left(4\right)$

Obtain the estimated value of current transmission frame inherent spurious frequency deviation Wherein L is the length of Cyclic Prefix.Order $\widehat{\mathrm{\&epsiv;}}={\widehat{\mathrm{\&epsiv;}}}_i+\widehat{\mathrm{\&epsiv;}},\widehat{\mathrm{\&epsiv;}}$ As the frequency offset estimating value to be used for the next frame signal correction.The base station before receiving the correction flag bit that user u sends, inherent spurious frequency deviation of every estimation, estimated value will constantly be added to

On; After receiving flag bit, will

Zero setting immediately.

In (3) step, system utilizes step (1), (2) correction, estimates frequency deviation value, and this estimated value is used for the correcting frequency deviation of next frame signal;

The frequency deviation value that the former frame that system utilized for (2) step to be provided is estimated is corrected this frame signal by the process that (1) step described, and this frame signal after the correction utilized for (2) step obtained the frequency offset estimating value then, corrected the next frame signal.

Because to be subjected to The noise, this estimated value is a stochastic variable, the precision that the mean square error by calculating this estimated value and real surplus frequency deviation can method of estimation.

The present invention is based on the carrier frequency tracking method of signal reconstruction, adopts local calculation process to correct with feedback and corrects the mode that combines, and computation complexity is low, realize simply, but following range is bigger, and tracking velocity is fast, and the precision height has improved efficiency of transmission.This method can be used for OFDMA and DFT-SOFDM up link, finish capturing frequency deviation after, utilize this method to carry out frequency offset tracking.

Description of drawings

Fig. 1 is a system block diagram of realizing method proposed by the invention.

Fig. 2 is the normal tracking characteristics figure of the inventive method under block groups of subchannels.

Fig. 3 is the normal tracking characteristics figure of the inventive method under the pectination groups of subchannels.

Fig. 4 is the block groups of subchannels of the inventive method inherent spurious frequency deviation mean square error figure under different signal to noise ratios.

Fig. 5 is the inventive method pectination groups of subchannels inherent spurious frequency deviation mean square error figure under different signal to noise ratios.

Among the figure: 1, information source module, 2, the sign map module, 3, FFT module (M point), 4, the signal spectrum conversion module, 5, IFFT module (N point), 6, add Cyclic Prefix (CP) module, 7, the D/A module, 8, intermediate frequency and rf modulations module, 9, channel, 10, radio frequency and intermediate frequency demodulation module, 11, the A/D module, 12, go the CP module, 13, FFT module (N point), 14, the signal spectrum inverse transform block, 15, balance module, 16, IFFT module (M point), 17, judging module, 18, channel estimation module, 19, reconstructed module, 20, recover module, 21, the estimated bias computing module, 22, multiple access access control module, 23, synchronization module, 24, Postponement module, 25, the correcting frequency deviation module, 26, feedback channel, 27, the feedback judge module.

Embodiment

Embodiment

Fig. 1 has provided the system block diagram of realizing method proposed by the invention, and each module effect is as follows:

Information source module 1: general module, the data that generation will be transmitted.Produce the data of M length according to multiple access access module 22.

Sign map module 2: general module, the data based modulation system that adopts that information source is produced is mapped on the planisphere corresponding points.

M point FFT conversion module 3: general module, the individual mapping signal of every frame M is transformed to frequency domain, obtain the M point frequency-region signal of signal.

Signal spectrum conversion module 4: the base station is by multiple access access module 22, and the M point frequency-region signal that module 3 is exported is placed on the corresponding frequency spectrum point of M subchannel, is realized by the general digital signal processing chip.

N point IFFT module 5: general module transforms to time domain again with the frequency-region signal that newly obtains.

Add CP module 6: general module adds Cyclic Prefix with the every frame data that obtain.

D/A module 7: general module is an analog signal with digital signal conversion.

Intermediate frequency and rf modulations module 8: general module, if use this system under wireless environment, need make rf modulations to signal could the antennas emission.Need sometimes earlier signal to be modulated to carry out the intermediate frequency amplification on the intermediate frequency, remake rf modulations, at last the modulated signal antennas is launched.

Channel 9: general module, the broadband mobile channel of transmission signals.

Radio frequency and intermediate frequency demodulation module 10: general module, in wireless environment, the frequency spectrum that reception antenna is received signal is moved low frequency from radio frequency or intermediate frequency.Before demodulation, need the frequency deviation that causes with in the Frequency Synchronization data correction signal transmission course.

A/D module 11: general module is transformed to digital signal with analog signal after the demodulation.A/D need sample to analog signal, provides the crystal oscillator of clock signal need follow the crystal oscillator frequency of transmitter D/A module identical, otherwise will cause the sampling rate error.Therefore it is synchronous to carry out sampling rate before A/D.

Go CP module 12: general module, remove Cyclic Prefix.At this moment just have the problem of judging when frame data begin, therefore going needs to do regularly synchronously before the CP.

N point FFT module 13: general module, will remove the signal of CP and the signal transformation of correcting frequency deviation module 25 outputs and arrive frequency domain.

Signal spectrum inverse transform block 14:, find out M point frequency-region signal that the received signal sub-channels carries and signal exported to and recover module 20 according to multiple access access module 22.

Balance module 15: general module, with the subchannel parameter (channel condition information) that channel estimation module 18 is sent here, the signal that signal spectrum inverse transform block 14 is elected carries out equilibrium.Balanced way can be selected one of following three kinds of balanced ways: zero forcing equalization, least mean-square error equilibrium, mixed mode equilibrium.

M point IFFT conversion module 16: general module transforms to time domain with M frequency-region signal of signal after the equilibrium.

Judging module 17: general module, according to the modulation system that system adopted, finish the judgement of time-domain signal and signal is exported to reconstructed module 19.

Channel estimation module 18: general module, carry out channel status and obtain.Can obtain channel condition information with diverse ways, as channel estimating, based on the channel estimation methods of auxiliary data, decision-feedback channel tracking method etc.It is training frames that embodiment provides the channel status acquisition methods.The following formation of each user's training frames.At first, produce the Newmann sequence:

$X_m=A\frac{\mathrm{\&pi;}{\mathrm{<figure-callout\; id="0"\; label="m"\; filenames="A20061006925900141.png"\; state="\{\{state\}\}">m</figure-callout>}}^2}{M},0\&le;m\&le;M-1$

Here A is an amplitude.If the signal to noise ratio of accepting of training frames is snr, amplitude is provided by following formula:

$A=\sqrt{\frac{\mathrm{<figure-callout\; id="10"\; label="N"\; filenames="A20061006925900131.png,A20061006925900141.png"\; state="\{\{state\}\}">N</figure-callout>}{10}^{\frac{\mathrm{<figure-callout\; id="10"\; label="snr"\; filenames="A20061006925900131.png,A20061006925900141.png"\; state="\{\{state\}\}">snr</figure-callout>}}{10}}{\mathrm{\&sigma;}}^2}{M}}$

σ ²It is noise power.Then, this sequence is expanded into the N dimensional vector

By N point IFFT conversion, ${\tilde{x}}^u=\mathrm{IFFT}\left({\tilde{x}}^u\right)$ Obtain each user's training frames.Remove CP after crossing channel, acknowledge(ment) signal r=(r _n, r ₁..., r _N-1), doing N point FFT conversion, R=FFT (r) is obtained the frequency domain estimated value of channel by following formula:

$\widetilde{H_m^u}=\frac{R_{k_m}}{X_{k_m}},0\&le;m\&le;M-1$

Owing to adopted the high accuracy frequency bias capture method, frequency deviation can be ignored the influence of channel estimating.

Reconstructed module 19: the signal reconstruction of judging module 17 inputs is gone out

Storage

Real part and imaginary part.

Recover module 20: the signal of signal spectrum inverse transform block 14 inputs is recovered

Storage Real part and imaginary part.

Estimated bias computing module 21: according to reconstructed module 19 outputs With 20 outputs of recovery module

Real part and imaginary part, according to formula ${\widehat{\mathrm{\&epsiv;}}}_i=\frac{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="A20061006925900131.png,A20061006925900141.png"\; state="\{\{state\}\}">N</figure-callout>}}{2\mathrm{\&pi;}}\frac{\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}(n+L)(y_n{a}_n-x_n{b}_n)}{\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{(n+L)}^2(a_{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="A20061006925900131.png,A20061006925900141.png"\; state="\{\{state\}\}">n</figure-callout>}}^2+b_n^2)}$ Calculate the estimated value of current transmission frame inherent spurious frequency deviation By formula $\widehat{\mathrm{\&epsiv;}}={\widehat{\mathrm{\&epsiv;}}}_i+\widehat{\mathrm{\&epsiv;}},$ Calculate the frequency offset estimating value, give feedback judge module 27 result of calculation.

Multiple access access control module 22: when setting up communication, the base station obtains each user's channel condition information by channel estimation module 18, for each user's allocated sub-channels group and user's access is as the criterion insert synchronously.The function of this module is with the multiple access access control module among the OFDMA.It is block setting up groups of subchannels u in the present embodiment, and the number of sub-channels of all groups of subchannels u all is identical, leaves 1 virtual carrier between groups of subchannels.

Synchronization module 23: this module is made up of three submodules, comprises regularly submodule, the synchronous submodule of sampling rate and carrier frequency acquisition submodule synchronously.Synchronization module 23 obtains the various synchrodatas that system needs by parameter Estimation.The carrier frequency acquisition submodule is given radio frequency and intermediate frequency demodulation module 10 with the Frequency Synchronization data; The synchronous submodule of sampling rate is given analog-to-digital conversion module 11 with the sampling rate synchrodata; Regularly submodule is given CP module 12 with the timing synchrodata synchronously.

Postponement module 24: by feeding back the frequency offset estimating value that judge module 27 obtains

Postpone a frame, give correcting frequency deviation module 25, correct the received signal that next frame contains frequency deviation.

Correcting frequency deviation module 25: according to the inherent spurious frequency deviation estimated value of the output of the frequency offset tracking submodule in the synchronous submodule

By formula $r_n^{\widehat{\mathrm{\&epsiv;}}}=r_n{e}^{\frac{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20061006925900131.png,A20061006925900141.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}\widehat{\mathrm{\&epsiv;}(n+L)}}{N}},$ N=0,1 ..., N-1 corrects received signal, and the result sends into N point FFT module 13.

Feedback channel 26: will feed back the frequency offset estimating value that judge module 27 obtains and pass to compensate of frequency deviation module 28, the information of multiple access access control module 22 is passed to signal spectrum conversion module 4.

Feedback judge module 27: if work as when normally following the tracks of $\widehat{\mathrm{\&epsiv;}}>{\mathrm{\&delta;}}_1$ Several times appear continuously, for example 3 times the time or when following the tracks of first $\stackrel{-}{\mathrm{\&epsiv;}}<{\mathrm{\&delta;}}_0,$ Then with the frequency offset estimating value Pass to compensate of frequency deviation module 28 by feedback channel 26, otherwise give Postponement module 24 the frequency offset estimating value.

Compensate of frequency deviation module 28: the frequency offset estimating value that feedback channel 26 transmits is adjusted intermediate frequency and rf modulations module 8.

This embodiment simulation parameter:

Simulated environment: Matlab7.0.1, the representative channel sample of IMT-2000 Vehichlar Test Environment channel model A, the every frame of carrier wave frequency deviation has 0.1% linear drift, and channel estimating adopts training frames and received signal to noise ratio with respect to the many 2dB of Frame

Subchannel sum: N=1024

Modulation system: 16QAM

CP length: 128

Number of users: 16

Received signal to noise ratio: 14dB (16QAM)

Fig. 2 has provided the tracking characteristics of the inventive method under block groups of subchannels.Fig. 3 has provided the tracking characteristics of the inventive method under the pectination groups of subchannels.The influence of error code supposes that promptly propagation delay time and error code all are 0 when propagation delay time when not considering backward channel passback frequency offset estimating value and transmission frequency deviation estimated value.Fig. 4 has provided the block groups of subchannels of the inventive method inherent spurious frequency deviation mean square error under different signal to noise ratios.Fig. 5 has provided the inventive method pectination groups of subchannels inherent spurious frequency deviation mean square error figure under different signal to noise ratios.Every some emulation 10,000 frames.

Simulation result shows that this method tracking velocity is fast, and the precision height is locked in relative frequency deviation in positive and negative 2%, satisfies the requirement of system to the frequency offset tracking precision fully, has very high practical value.Outstanding advantage of the present invention is: computation complexity is low, and particularly amount of calculation is little, and the estimated accuracy height is realized simply not reducing the spectrum efficiency of system, belongs to blind estimation tracking truly.

For avoiding confusion, following explanation done in some nouns of being mentioned in this specification:

1. symbol: be meant the data of information bit after ovennodulation mapping (also claiming sign map).It generally is the plural number that a real part and imaginary part are integer.

2. frame signal: for OFDM, a frame signal is meant N symbol doing the IFFT conversion at transmitting terminal, is meant at receiving terminal and is removing N the symbol that CP does the FFT conversion later on.For the DFT-SOFDM system, a frame signal is meant N information symbol between adjacent two CP at transmitting terminal, is meant at receiving terminal and is removing N the symbol that CP does the FFT conversion later on.

Claims (5)

1. the carrier frequency tracking method of a multi user block transmission system up link is characterized in that: meeting the following conditions down: after a user u process carrier wave frequency deviation is caught, remain relative carrier wave frequency deviation to be controlled in 2%; B regularly finishes synchronously; This carrier frequency tracking method may further comprise the steps:

(1) system enters normal tracking mode, the up time domain baseband signal of the original multi-user that the base station will receive r=( r ₀, r ₁..., r _N-1 ) be each user ID, the base station utilizes the frequency offset estimating value to rectify a deviation, and selected simultaneously passback frequency offset estimating is worth needed correction thresholding δ ₁

(2) result who estimates and adjudicate according to current frame channel, the corresponding time-domain signal that does not contain frequency deviation of the signal of base station reconfiguration and user u, and recover the time-domain signal that contains frequency deviation of user u according to the groups of subchannels of user u, according to the signal that contains frequency deviation and the reconstruction signal that recover, calculate the estimated value of frequency deviation;

(3) utilize step (1), (2) correction, estimate frequency deviation value, this estimated value is used for the correcting frequency deviation of next frame signal.

2. the carrier frequency tracking method of multi user block transmission system up link according to claim 1 is characterized in that: the implementation method in described (1) step is:

The frequency offset estimating value of supposing present frame is , the base station utilizes this estimated value to carry out the time domain correction, establishes the correction thresholding to be δ ₁, adopt the feedback method for correcting error:

If , in order to reduce The noise, when When several times occurring continuously, receiving terminal feeds back to it user u again, and user u rectifies a deviation, with the error signal of the frequency deviation value of receiving as transmission vibrator phase-locked loop, with phase-locked loop tranmitting frequency is finely tuned, after user u end is finished correcting frequency deviation, send a correction complement mark position.

3. the carrier frequency tracking method of multi user block transmission system up link according to claim 1 is characterized in that: the implementation method in described (1) step is:

The frequency offset estimating value of supposing present frame is , the base station utilizes this estimated value to carry out the time domain correction, establishes the correction thresholding to be δ ₁, adopt local method for correcting error:

If

, the base station utilizes formula $r_n^{\widehat{\mathrm{\&epsiv;}}}=r_n{e}^{\frac{-j2\mathrm{\&pi;}\widehat{\mathrm{\&epsiv;}}(n+L)}{N}},n=\mathrm{0,1},...,N-1$ , to the up time domain baseband signal of the original multi-user who receives r=( r ₀, r ₁..., r _N-1 ) rectify a deviation.

4. the carrier frequency tracking method of multi user block transmission system up link according to claim 1 is characterized in that: the implementation method of described (2) step for the OFDMA system is:

To r correction processing, the signal that obtains is designated as according to (1) process that goes on foot description , right Carry out NPoint FFT conversion, that is:

$Y=\mathrm{FFT}\left(r^{\widehat{\mathrm{\&epsiv;}}}\right)$

Obtain the frequency-region signal of user u by following formula:

$Y^u=(Y_{k_0},Y_{k_1},...,Y_{k_{M-1}})=(Y_0^u,...,Y_{M-1}^u)$

Obtain the frequency domain characteristic of user u up channel by channel estimating ${\tilde{H}}_{k_m}^u,(m=\mathrm{0,1},...,M-1)$ , then to Y _m ^u, ( m=0,1 ..., M-1) carries out frequency domain equalization, balanced data according to the modulation system judgement of adopting, is obtained the Frame symbol after user u adjudicates ${\tilde{S}}_m^u,(m=\mathrm{0,1},...,M-1),$ Its bit error rate is lower, less than 10 ^-1To 10 ^-3Magnitude, wherein MBe the number of subchannels of u user's groups of subchannels, this moment, judging process was eliminated most frequency deviations and The noise; During reconstruction signal, utilize , ( m=0,1 ..., M-1), according to formula:

And it is right Do NPut the IFFT conversion, reconstruct the time domain form of the received signal that does not contain frequency deviation

, promptly ${\tilde{y}}^u=\mathrm{IFFT}\left({\tilde{Y}}^u\right);$

According to following formula, obtain the frequency domain information of user u:

It is carried out NPoint IFFT conversion, the time domain form signal that contains frequency deviation of recovery user u, promptly

Because containing the recovery value of the received signal time domain form of inherent spurious frequency deviation all is complex vector located with the reconstruction value that does not contain frequency deviation, respectively their component is write as:

${\hat{y}}_n^u=x_n+j{y}_n,n=\mathrm{0,1},...,N-1$

${\tilde{y}}_n^u=a_n+j{b}_n,n=\mathrm{0,1},...,N-1$

By formula

${\widehat{\mathrm{\&epsiv;}}}_i=\frac{N}{2\mathrm{\&pi;}}\frac{\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}(n+L)(y_n{a}_n-x_n{b}_n)}{\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{(n+L)}^2(a_n^2+b_n^2)}$

Obtain the estimated value of current transmission frame inherent spurious frequency deviation , wherein L is the length of Cyclic Prefix; Order

,

As the frequency offset estimating value to be used for the next frame signal correction; The base station before receiving the correction flag bit that user u sends, inherent spurious frequency deviation of every estimation, estimated value will constantly be added to

On; After receiving flag bit, will

Zero setting immediately.

5. the carrier frequency tracking method of multi user block transmission system up link according to claim 1 is characterized in that: the implementation method of described (2) step for the DFT-SOFDM system is:

To r correction processing, the signal that obtains is designated as according to (1) process that goes on foot description

, right Carry out NPoint FFT conversion, that is:

$Y=\mathrm{FFT}\left(r^{\widehat{\mathrm{\&epsiv;}}}\right)$

Obtain the frequency-region signal of user u by following formula:

$Y^u=(Y_{k_0},Y_{k_1},...,Y_{k_{M-1}})=(Y_0^u,Y_1^u,...,Y_{M-1}^u)$

Obtain the frequency domain characteristic of user u up channel by channel estimating ${\tilde{H}}_{k_m}^u,(m=\mathrm{0,1},...,M-1),$ Then to Y _m ^u, ( m=0,1 ..., M-1) carries out frequency domain equalization, balanced data is done MPoint IFFT conversion is adjudicated the modulation system of the data based employing behind the IFFT again, obtains the Frame symbol after user u adjudicates ${\tilde{S}}_m^u,(m=\mathrm{0,1},...,M-1),$ Its bit error rate is lower, less than 10 ^-1To 10 ^-3Magnitude, wherein MBe the number of subchannels of u user's groups of subchannels, this moment, judging process was eliminated most frequency deviations and The noise; During reconstruction signal, will ${\tilde{S}}_m^u,(m=\mathrm{0,1},...,M-1),$ Do MPoint FFT conversion, promptly ${\tilde{S}}^u=\mathrm{FFT}\left({\tilde{S}}^u\right)$ , according to formula:

And it is right ${\tilde{y}}^u=({\tilde{Y}}_0^u,{\tilde{Y}}_1^u,...,{\tilde{Y}}_{N-1}^u)$ Do N point IFFT conversion, reconstruct the time domain form of the received signal that does not contain frequency deviation

, promptly ${\tilde{y}}^u=\mathrm{IFFT}\left({\tilde{Y}}^u\right)$

According to following formula, the frequency domain information of the user u that obtains:

It is carried out NPoint IFFT conversion, the time domain form signal that contains frequency deviation of recovery user u, promptly ${\hat{y}}^u=\mathrm{IFFT}\left({\hat{Y}}^u\right)$

Because containing the recovery value of the received signal time domain form of inherent spurious frequency deviation all is complex vector located with the reconstruction value that does not contain frequency deviation, respectively their component is write as:

${\hat{y}}_n^u=x_n+j{y}_n,n=\mathrm{0,1},...,N-1$

${\hat{y}}_n^u=a_n+j{b}_n,n=\mathrm{0,1},...,N-1$

By formula

${\widehat{\mathrm{\&epsiv;}}}_i=\frac{N}{2\mathrm{\&pi;}}\frac{\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}(n+L)(y_n{a}_n-x_n{b}_n)}{\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{(n+L)}^2(a_n^2+b_n^2)}$

Obtain the estimated value of current transmission frame inherent spurious frequency deviation

, wherein L is the length of Cyclic Prefix; Order

,

As the frequency offset estimating value to be used for the next frame signal correction; The base station before receiving the correction flag bit that user u sends, inherent spurious frequency deviation of every estimation, estimated value will constantly be added to On; After receiving flag bit, will Zero setting immediately.

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