CN102185822B  OFDM/OQAM (Orthogonal Frequency Division Multiplexing/Offset Quadrature Amplitude Modulation) system and time frequency synchronization method thereof  Google Patents
OFDM/OQAM (Orthogonal Frequency Division Multiplexing/Offset Quadrature Amplitude Modulation) system and time frequency synchronization method thereof Download PDFInfo
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 CN102185822B CN102185822B CN 201110142938 CN201110142938A CN102185822B CN 102185822 B CN102185822 B CN 102185822B CN 201110142938 CN201110142938 CN 201110142938 CN 201110142938 A CN201110142938 A CN 201110142938A CN 102185822 B CN102185822 B CN 102185822B
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Abstract
The invention discloses an OFDM/OQAM (Orthogonal Frequency Division Multiplexing/Offset Quadrature Amplitude Modulation) system and a time frequency synchronization method thereof. The time frequency synchronization method comprises the following steps of: a coarse synchronization estimating step for estimating an estimated frequency offset value of a received baseband receiving signal frame sequence; a frequency offset compensating step for compensating the frequency offset of the received base band receiving signal frame sequence by using the estimated frequency offset value obtained by the coarse synchronization estimating step; a fine synchronization estimating step for estimating an estimated time offset value of r2 (KTS) obtained by the frequency offset compensating step; and a time offset compensating step for compensating the time offset of the r2 (kTS) obtained by the frequency offset compensating step by using the estimated time offset value obtained by the fine synchronization estimating step so as to obtain r3 (kTS). In the invention, onestep synchronization is divided into two steps including coarse synchronization and fine synchronization; and the frequency offset of the baseband receiving signal frame sequence is first compensated by using the estimated frequency offset value obtained in the coarse synchronization and then the fine synchronization is carried out by using the compensated signal to obtain a final estimated time offset value so that the influence of CFO (Carrier Frequency Offset) during the fine synchronization is minimized and the time offset estimation accuracy and the acquisition probability are improved.
Description
Technical field
The invention belongs to the mobile communication technology field, be particularly related to a kind of OFDM (OFDM/OQAM, Orthogonal Frequency Division Multiplexing/Offset Quadrature Amplitude Modulation) system and timefrequency synchronization method thereof of staggered quadrature amplitude modulation.
Background technology
Because wireless user's improving constantly transmission rate request, multicarrier modulation technology has become the main flow modulation system of present radio communication, as based on conventional orthogonal frequency division multiplexing (CPOFDM, the Cyclic PrefixOrthogonal Frequency Division Multiplexing) technology of Cyclic Prefix with regard to selected be key technology in the LTE standard.And for CPOFDM, OFDM/OQAM has higher spectrum efficiency, better timefrequency focus characteristics, and for overcoming intersymbol interference (ISI, InterSymbol Interference) and intercarrier interference (ICI, InterCarrier Interference) influence has good effect to a certain extent, the latter particularly becomes OFDM/OQAM with respect to one of main advantage of CPOFDM.The transmission signal of OFDM/OQAM system is realvalued, takes from real part and the imaginary part of complex symbol to be passed, and with respect to traditional ofdm system, OFDM/OQAM only satisfies strict orthogonality condition in real number field; Optional usefulness has the isotropism orthogonal transform function (IOTA, Isotropic Orthogonal Transform Algorithm) that good timefrequency focuses on (TFL, Time Frequency Localization) characteristic.
Use the OFDM/OQAM system sending end structure schematic diagram of traditional timefrequency combination method of estimation as shown in Figure 1.Comprise signal source module, normal signal processing module, orthogonalization phase mapping module, N point IFFT module, shaping filter module, D/A modular converter, upconversion module.
For the convenience of describing, at first introduce wherein used term:
(1) shaping filter function g (t) is at interval t ∈ { 0, T
_{s}..., (N
_{g}1) T
_{s}On get nonzero value, N wherein
_{g}=ξ T/T
_{s}For nonzero sample is counted, ξ is the tap number of shaping filter function, T
_{s}Be the systematic sampling time interval, T is the symbol time interval.
(2) frequency domain synchronizing pilot symbol is by the N of continuous transmission
_{TR}Individual OFDM symbol constitutes (N
_{TR}At least bigger 2 than the tap number ξ of shaping filter function, could guarantee so partly has the repetition frequency pilot sign through the time domain pilot of transmitting terminal modulation), be about to frequency domain repetition frequency pilot sign and be expressed as a
_{l}(p)=a
_{l} ^{TR}, l=0 ..., N1, p=0 ..., N
_{TR}1, wherein N represents subcarrier number, and l represents the sequence number of subcarrier, and p represents the frequency pilot sign sequence number.Through the timedomain pilot signal s after the modulation of transmitting terminal
_{TR}(kT
_{s}), k ∈ 0,1,2 ..., N
_{TR}N1} is at transmission N
_{g}After 2 sampled points ofN, at interval k ∈ { N of the moment
_{g}N/2 ..., N
_{TR}NN1} satisfies relational expression s
_{TR}(kT
_{s}+ NT
_{s})=s
_{TR}(kT
_{s}).
(3) the baseband receiving signals frame sequence is r (kT
_{s}), k ∈ 0,1,2 ..., τ ∈ 0,1 ..., inclined to one side actual value when N/4} is,
For the time inclined to one side estimated value,
For the time inclined to one side experiment value, ε ∈＜0.5,0.5〉for normalizing to frequency deviation actual value on the subcarrier spacing,
Be the frequency deviation estimated value,
Be correlated series,
For asking phase angular operator, τ
_{Max}Be the multipath channel maximum delay, D is the summation window length of sliding.
At first carry out initialization process: in the register of transmitting terminal (travelling carriage) and receiving terminal (base station), store identical transmission pilot frequency sequence, and will send time domain pilot sequence s at receiving terminal
_{TR}(kT
_{s}) ξ N+1 to the (N
_{TR}1) N data save as the transmission consensus sequence, in the identical shaping filter sequence of function of transmittingreceiving twoend storage, and set up corresponding rule.Concrete treatment step is as follows:
Step 11. signal source module produces data bit and does coding through the normal signal processing module, quadrature amplitude modulation (QAM, Quadrature Amplitude Modulation), obtain complex data after, framing and to add length at front end be N
_{TR}Frequency domain repeat frequency pilot sign a
_{l}(p)=a
_{l} ^{TR}, l=0 ..., N1, p=0 ..., N
_{TR}1, then carry out real imaginary component from;
Step 12. is carried out the orthogonalization phase mapping by orthogonalization phase mapping module respectively by the real imaginary part of the data that step 11 obtains;
Step 13. is done antifast Fourier transform (IFFT, Inverse Fast Fourier Transform) by the data of step 12 by N point IFFT module, finishes multicarrier modulation;
The data that step 14. is obtained by step 13 by the shaping filter module, are finished the signal moulding, and the string conversion;
Step 15. is transmitted by data process D/A modular converter, upconversion module that step 14 obtains.
As typical multicarrier modulation, OFDM/OQAM has the general character of a multicarrier modulation technology, namely be subject to carrier frequency shift (CFO, Carrier Frequency Offset) and the influence of time migration, the main cause that CFO produces is because the oscillator of transmittingreceiving twoend is stable and accurate inadequately, the frequency that produces is deviation to some extent, and then has destroyed the orthogonality between subcarrier, and then has introduced ISI and ICI.And owing to do not add CP, in case synchronism deviation occurs, whole discrete Fourier (DFT, Discrete Fourier Transform) window will misplace, and causes the interference that is difficult to recover, so partially also very responsive when OFDM/OQAM is.
In order to obtain reasonable systematic function, frequency deviation is estimated all to have than higher precision in the time of just must guaranteeing.T.Fusco, A.Petrella and M.Tanda " DataAided Symbol Timing and CFO Synchronization for Filter Bank Multicarrier Systems[J] .IEEE Trans.Wireless Commun.; May2009; 8 (5): 27052715. " proposed based on the autocorrelative MLS timefrequency combination of baseband receiving signals frame sequence second order method of estimation, also enumerated based on the baseband receiving signals frame sequence and sent the TR2 timefrequency combination method of estimation that consensus sequence carries out the quadravalence crosscorrelation.
Fig. 2 is for using the OFDMA/OQAM system receiving terminal fundamental diagram that traditional MLS and TR2 timefrequency combination are estimated, comprise down conversion module, the A/D modular converter, synchronous estimation module, the time compensate of frequency deviation module, matched filtering module, FFT module, go orthogonalization phase mapping module, the normal signal processing module.Suppose that the receiving terminal channel information is known, then the demodulation step of receiving terminal can be expressed as following step:
Step 21. receives signal through down conversion module, A/D modular converter, obtains baseband receiving signals frame sequence r (kT
_{s}), k ∈ 0,1,2 ...;
The baseband receiving signals frame sequence r (kT that step 22. obtains step 21
_{s}) frequency deviation when estimating by synchronization module, be (N by the baseband receiving signals frame sequence is carried out length
_{TR}1ξ) (processing method that MLS timefrequency combination method of estimation adopts specifically can be expressed as the slip autocorrelation of N+1
Wherein,
Obtain a correlated series
Choose
Inclined to one side experiment value when peak value is corresponding
As the time inclined to one side estimated value
Recycling
Further estimate the frequency deviation estimated value
Here, " " expression phase multiplication, " * " represents conjugate operation;
During step 23. the compensate of frequency deviation module with step 22 obtain the time partially and the frequency deviation estimated value baseband receiving signals frame sequence is compensated;
The data that step 24. obtains step 23 are done matched filtering by the matched filtering module;
Step 25. will through fast Fourier transform (FFT, Fast Fourier Transform) module, be finished the multicarrier demodulation by the data after the step 24;
Step 26. will be gone the orthogonalization phase mapping through past orthogonalization phase mapping module by the data after the step 25;
Step 27. will be by the data after the step 26, eliminate via equalizer (as zero forcing equalization etc.) or reduce multipath channel to the influence of OFDM/OQAM signal with known channel information;
Step 28. will be carried out real imaginary part by the data after the step 27 and be converged, and carry out QAM demodulation and corresponding decoding, the output data bit.
Here adopt the OFDM/OQAM system of traditional timefrequency combination method of estimation based on pilot tone to have following shortcoming:
One, receiving terminal has only carried out associative operation one time, when estimating after the inclined to one side estimated value of offset frequency when having carried out at once the offset frequency offset compensation, estimate partially when noticing before frequency deviation is estimated, to carry out, that is to say the influence of not removing frequency deviation when when carrying out, estimating partially, the acquisition probability of having estimated partially when this has also influenced.
They are two years old. directly choose by step 22 obtain the correlated series peak value when corresponding inclined to one side experiment value as the time inclined to one side estimated value.When first footpath was not the strongest path of instantaneous power in multipath channel, the time inclined to one side estimated value that obtains like this can automatically become locked on the footpath of instantaneous power maximum, rather than first footpath of wishing.Can directly cause the demodulation operation dislocation of receiving terminal step 24 and step 25 like this, cause correctly demodulation of receiving terminal.
They are three years old. two kinds of methods estimating partially when step 22 is used for.First method adopts baseband receiving signals frame sequence second order autocorrelation estimating time bias, and the correlation that obtains like this changes milder, than the influence that is easier to be subjected to noise and CFO; Second method adopts the baseband receiving signals frame sequence and sends the quadravalence slip crosscorrelation estimating time bias of consensus sequence, and the correlation that obtains like this can obtain than higher relevant peaks at the timing point, but the complexity that realizes increases to some extent.
They are four years old. the slip correlation window scope (N that step 22 is chosen when carrying out associative operation
_{TR}1ξ) N does not arrive the maximum magnitude that can choose in theory, and inclined to one side estimated accuracy also has certain room for improvement when that is to say.And the frequency deviation estimated value is that inclined to one side estimated value calculates when utilizing, and improved space is also arranged.
Summary of the invention
The objective of the invention is the lower problem of acquisition probability estimated partially when solving existing employing based on the OFDM/OQAM system of the timefrequency combination method of estimation of pilot tone, proposed a kind of OFDM/OQAM system and timefrequency synchronization method thereof.
Technical scheme of the present invention is: a kind of OFDM/OQAM system is characterized in that the receiving terminal of described OFDM/OQAM system comprises:
Thick estimation module synchronously is used for the baseband receiving signals frame sequence r that estimation receives
_{1}(kT
_{S}) the frequency deviation estimated value
The compensate of frequency deviation module is used for the frequency deviation estimated value that thick estimation module is synchronously obtained
To baseband receiving signals frame sequence r
_{1}(kT
_{S}) carry out compensate of frequency deviation, obtain the receiving symbol frame sequence r behind the compensate of frequency deviation
_{2}(kT
_{S});
Thin estimation module synchronously is used for the r that estimates that the compensate of frequency deviation module obtains
_{2}(kT
_{S}) time inclined to one side estimated value
The partial compensation for the time module is used for the time inclined to one side estimated value that thin estimation module is synchronously obtained
The r that the compensate of frequency deviation module is obtained
_{2}(kT
_{S}) carry out partial compensation for the time, the receiving symbol frame sequence r when obtaining behind the compensate of frequency deviation
_{3}(kT
_{S}).
The invention allows for a kind of OFDM/OQAM system time frequency method for synchronous, comprise
Thick estimating step synchronously is used for the baseband receiving signals frame sequence r that estimation receives
_{1}(kT
_{S}) the frequency deviation estimated value
The compensate of frequency deviation step is used for the frequency deviation estimated value that thick estimating step is synchronously obtained
To the baseband receiving signals frame sequence r that receives
_{1}(kT
_{S}) carry out compensate of frequency deviation, obtain the receiving symbol frame sequence r behind the compensate of frequency deviation
_{2}(kT
_{S});
Thin estimating step synchronously is used for the r that estimates that the compensate of frequency deviation step obtains
_{2}(kT
_{S}) time inclined to one side estimated value
The partial compensation for the time step is used for the time inclined to one side estimated value that thin estimating step is synchronously obtained
The r that the compensate of frequency deviation step is obtained
_{2}(kT
_{S}) carry out partial compensation for the time, the receiving symbol frame sequence r when obtaining behind the compensate of frequency deviation
_{3}(kT
_{S}).
As a preferable scheme of the present invention, the detailed process of described thick estimating step synchronously is as follows:
With baseband receiving signals frame sequence r
_{1}(kT
_{S}) and send consensus sequence s
_{TR}(kT
_{s}) to carry out length be (N
_{TR}ξ12) the second order slip computing crosscorrelation of N obtains a correlated series
Specifically be expressed as
Wherein
${R}_{1}\left(\stackrel{~}{\mathrm{\τ}}\right)=\underset{k={N}_{g}N/2}{\overset{{N}_{\mathrm{TR}}\·NN1}{\mathrm{\Σ}}}{r}_{1}^{*}(k{T}_{s}+\stackrel{~}{\mathrm{\τ}}){s}_{\mathrm{TR}}\left(k{T}_{s}\right),$ $Q\left(\stackrel{~}{\mathrm{\τ}}\right)=\underset{k={N}_{g}N/2}{\overset{{N}_{\mathrm{TR}}\·NN1}{\mathrm{\Σ}}}{\left{s}_{\mathrm{TR}}\left(k{T}_{s}\right)\right}^{2},$ Right
The slip summation operation of carrying out the long D of fixed window obtains one and sequence
D＞τ wherein
_{Max}, choose and sequence
Peak value inclined to one side test value when corresponding
As the time inclined to one side estimated value
Use again
Further estimate the frequency deviation estimated value
Wherein
Wherein, N is subcarrier number, N
_{TR}For frequency domain repeats frequency pilot sign number, N
_{g}For the nonzero sample of shaping filter function is counted T
_{s}Be the sampling period.
As another preferable scheme of the present invention, the detailed process of described thin estimating step synchronously is as follows:
The compensate of frequency deviation step is obtained r
_{2}(kT
_{S}) and send consensus sequence s
_{TR}(kT
_{s}) to carry out length be (N
_{TR}ξ1/2) the second order slip computing crosscorrelation of N obtains a correlated series
Specifically be expressed as
Wherein
${R}_{2}\left(\stackrel{~}{\mathrm{\τ}}\right)=\underset{k={N}_{g}N/2}{\overset{{N}_{\mathrm{TR}}\·NN1}{\mathrm{\Σ}}}{r}_{2}^{*}(k{T}_{s}+\stackrel{~}{\mathrm{\τ}}){s}_{\mathrm{TR}}\left(k{T}_{s}\right),$ $Q\left(\stackrel{~}{\mathrm{\τ}}\right)=\underset{k={N}_{g}N/2}{\overset{{N}_{\mathrm{TR}}\·NN1}{\mathrm{\Σ}}}{\left{s}_{\mathrm{TR}}\left(k{T}_{s}\right)\right}^{2},$ Right
The slip summation operation of carrying out the long D of fixed window obtains one and sequence
D＞τ wherein
_{Max}, choose and sequence
Peak value inclined to one side test value when corresponding
As the time inclined to one side estimated value
Wherein, N is subcarrier number, N
_{TR}For frequency domain repeats frequency pilot sign number, N
_{g}For the nonzero sample of shaping filter function is counted T
_{s}Be the sampling period.
Beneficial effect of the present invention: the present invention expanded to for two steps with the step method for synchronous based on the timefrequency combination method of estimation of pilot tone in traditional OFDM/OQAM system, i.e. thick estimation is synchronously estimated synchronously with thin, with the frequency deviation estimated value that obtains in the thick estimation synchronously the baseband receiving signals frame sequence is carried out compensate of frequency deviation earlier, carry out the thin final time inclined to one side estimated value of estimating to obtain synchronously with the signal after the compensation again, make thin synchronously the time influence of CFO drop to minimum, precision and the acquisition probability estimated partially during raising; Expand the relevant range of baseband receiving signals frame sequence and transmission consensus sequence simultaneously, improved frequency offset estimation accuracy.
Adopt method and system of the present invention, the precision that the acquisition probability of estimating partially in the time of can effectively improving and frequency deviation are estimated is to reach the purpose that better satisfies the highspeed mobile communications requirement.
Description of drawings
Fig. 1 is the OFDM/OQAM system sending end structure schematic diagram that traditional timefrequency combination is estimated.
Fig. 2 is the OFDM/OQAM system receiving terminal structural representation that traditional timefrequency combination is estimated.
Fig. 3 is OFDM/OQAM system receiving terminal structural representation of the present invention.
Fig. 4 is the time inclined to one side acquisition probability contrast schematic diagram of method of the present invention and TR2, MLS method.
Fig. 5 is that the frequency deviation of method of the present invention and TR2, MLS method is estimated mean square error contrast schematic diagram.
Embodiment
The invention will be further elaborated below in conjunction with accompanying drawing and specific embodiment.
Of the present invention main by following technological means realization:
One, step method for synchronous based on the timefrequency combination method of estimation of pilot tone in traditional OFDM/OQAM system was expanded to for two steps, i.e. thick estimation is synchronously estimated synchronously with thin, with the frequency deviation estimated value that obtains in the thick estimation synchronously the baseband receiving signals frame sequence is carried out compensate of frequency deviation earlier, carry out thin estimation synchronously with the signal after the compensation again and obtain final time inclined to one side estimated value;
For the effect that further develops skill, in synchronously thick and thin synchronous estimation procedure, taked following measure:
Two, carrying out when synchronous with the baseband receiving signals frame sequence and sending consensus sequence to carry out the theoretical expanded range of crosscorrelation to maximum;
Three, change the related operation of receiving terminal into baseband receiving signals frame sequence and the second order computing crosscorrelation that sends consensus sequence;
Four, correlated series is carried out the summation of further sliding window handles, the peak value of choosing gained and sequence mould value as the time inclined to one side estimated value.
Be specifically described below.OFDM/OQAM system of the present invention and timefrequency synchronization method thereof, as shown in Figure 3, the receiving terminal of OFDM/OQAM system comprises:
Thick estimation module synchronously is used for the baseband receiving signals frame sequence r that estimation receives
_{1}(kT
_{S}) the frequency deviation estimated value
The compensate of frequency deviation module is used for the frequency deviation estimated value that thick estimation module is synchronously obtained
To the baseband receiving signals frame sequence r that receives
_{1}(kT
_{S}) carry out compensate of frequency deviation, obtain the receiving symbol frame sequence r behind the compensate of frequency deviation
_{2}(kT
_{S});
Thin estimation module synchronously is used for the r that estimates that the compensate of frequency deviation module obtains
_{2}(kT
_{S}) time inclined to one side estimated value
The partial compensation for the time module is used for the time inclined to one side estimated value that thin estimation module is synchronously obtained
The r that the compensate of frequency deviation module is obtained
_{2}(kT
_{S}) carry out partial compensation for the time, the receiving symbol frame sequence r when obtaining behind the compensate of frequency deviation
_{3}(kT
_{S}).
OFDM/OQAM system time frequency method for synchronous of the present invention comprises the steps:
Thick estimating step synchronously is used for the baseband receiving signals frame sequence r that estimation receives
_{1}(kT
_{S}) the frequency deviation estimated value
The compensate of frequency deviation step is used for the frequency deviation estimated value that thick estimating step is synchronously obtained
To the complex symbol frame sequence r that receives
_{1}(kT
_{S}) carry out compensate of frequency deviation, obtain the receiving symbol frame sequence r behind the compensate of frequency deviation
_{2}(kT
_{S});
Thin estimating step synchronously is used for the r that estimates that the compensate of frequency deviation step obtains
_{2}(kT
_{S}) time inclined to one side estimated value
The partial compensation for the time step is used for the time inclined to one side estimated value that thin estimating step is synchronously obtained
The r that the compensate of frequency deviation step is obtained
_{2}(kT
_{S}) carry out partial compensation for the time, the receiving symbol frame sequence r when obtaining behind the compensate of frequency deviation
_{3}(kT
_{S}).
Here the estimation procedure in thick estimating step synchronously and the thin estimating step synchronously can adopt MLS and the TR2 method in the background technology, and here as one of timefrequency synchronization method of the present invention preferable scheme, the detailed process of thick estimating step synchronously is as follows:
With baseband receiving signals frame sequence r
_{1}(kT
_{S}) and send consensus sequence s
_{TR}(kT
_{s}) to carry out length be (N
_{TR}ξ1/2) the second order slip computing crosscorrelation of N obtains a correlated series
Specifically be expressed as
Wherein
${R}_{1}\left(\stackrel{~}{\mathrm{\τ}}\right)=\underset{k={N}_{g}N/2}{\overset{{N}_{\mathrm{TR}}\·NN1}{\mathrm{\Σ}}}{r}_{1}^{*}(k{T}_{s}+\stackrel{~}{\mathrm{\τ}}){s}_{\mathrm{TR}}\left(k{T}_{s}\right),$ $Q\left(\stackrel{~}{\mathrm{\τ}}\right)=\underset{k={N}_{g}N/2}{\overset{{N}_{\mathrm{TR}}\·NN1}{\mathrm{\Σ}}}{\left{s}_{\mathrm{TR}}\left(k{T}_{s}\right)\right}^{2},$ Right
The slip summation operation of carrying out the long D of fixed window obtains one and sequence
D＞τ wherein
_{Max}, choose and sequence
Peak value inclined to one side test value when corresponding
As the time inclined to one side estimated value
Use again
Further estimate the frequency deviation estimated value
Wherein
$F\left(\stackrel{~}{\mathrm{\τ}}\right)=\underset{k={N}_{g}N/2}{\overset{{N}_{\mathrm{TR}}\·NN1}{\mathrm{\Σ}}}{r}_{1}(k{T}_{s}+N{T}_{s}+\stackrel{~}{\mathrm{\τ}}){r}_{1}^{*}(k{T}_{s}+\stackrel{~}{\mathrm{\τ}}).$
Here as another preferable scheme of timefrequency synchronization method of the present invention, detailed process is as follows in the thin estimating step synchronously:
The compensate of frequency deviation step is obtained r
_{2}(kT
_{S}) and send consensus sequence s
_{TR}(kT
_{s}) to carry out length be (N
_{TR}ξ1/2) the second order slip computing crosscorrelation of N obtains a correlated series
Specifically be expressed as
Wherein
${R}_{2}\left(\stackrel{~}{\mathrm{\τ}}\right)=\underset{k={N}_{g}N/2}{\overset{{N}_{\mathrm{TR}}\·NN1}{\mathrm{\Σ}}}{r}_{2}^{*}(k{T}_{s}+\stackrel{~}{\mathrm{\τ}}){s}_{\mathrm{TR}}\left(k{T}_{s}\right),$ $Q\left(\stackrel{~}{\mathrm{\τ}}\right)=\underset{k={N}_{g}N/2}{\overset{{N}_{\mathrm{TR}}\·NN1}{\mathrm{\Σ}}}{\left{s}_{\mathrm{TR}}\left(k{T}_{s}\right)\right}^{2},$ Right
The slip summation operation of carrying out the long D of fixed window obtains one and sequence
D＞τ wherein
_{Max}, choose and sequence
Peak value inclined to one side test value when corresponding
As the time inclined to one side estimated value
As can be seen, thick estimation module synchronously and thin estimation module synchronously can be respectively applied to realize abovementioned thick estimating step synchronously and the thin detailed process of estimating step synchronously here.
The present invention at first expanded to for two steps with the step method for synchronous based on the timefrequency combination method of estimation of pilot tone in traditional OFDM/OQAM system, namely synchronously thick and synchronously thin, with the thick middle frequency deviation estimated value that obtains synchronously the baseband receiving signals frame sequence is carried out compensate of frequency deviation earlier, carry out carefully obtaining synchronously final time inclined to one side estimated value with the signal after the compensation again, such processing make thin synchronously the time influence of CFO drop to minimum, the precision of estimating partially during raising; Secondly carrying out when synchronous the baseband receiving signals frame sequence and sending theoretical expanded range that consensus sequence carries out crosscorrelation to maximum, be i.e. (N
_{TR}ξ1/2) N can farthest utilize the reception data of frequency deviation information when carrying like this, makes estimated result more accurate; Related operation with receiving terminal changes baseband receiving signals frame sequence and the second order crosscorrelation that sends consensus sequence into again, such processing is directly done the autocorrelative timing accuracy height of second order than baseband receiving signals frame sequence, also the complexity of doing the quadravalence crosscorrelation than baseband receiving signals frame sequence and transmission consensus sequence is low, is guaranteeing to find a balance point preferably between estimated performance and the control implementation complexity; Moreover, the present invention be not directly with the correlated series peak value to seasonable test value partially as the time inclined to one side estimated value, but being carried out further sliding window summation, handles correlated series, the peak value of choosing gained and sequence mould value as the time inclined to one side estimated value, when the starting end of the summation window that slides just aligns the channel impulse response in first footpath, all path responses of multipath channel are all in the summation window, what obtain is maximum with value, and when first directly is moved out of outside the summation window, decline to a certain degree appears in meeting with value, so choose when corresponding with the peak value of sequence inclined to one side test value as the time inclined to one side estimated value, can be locked in comparatively exactly on the time of advent in first footpath.The bias estimation footpath that instantaneous power is the strongest in multipath channel is not can be locked in the power most powerful path and the timing error that causes under the situation in first footpath in the time of can solving tradition effectively like this.
Present embodiment adopts following system condition: OFDM/OQAM system subcarrier number is 256, and the shaping filter function is selected the IOTA function, and repetition pilot length N is chosen in the tap number ξ of filter=8
_{TR}=10 data symbols, adopt the 4QAM modulation, sample frequency: be 4M(million)the sample per second, adopt 802.22 representative channel in 6 footpaths, channel delay is [3024711] (unit is sampling time interval), path gain is [607221620] (unit is dB), and (carrier spacing), normalization Doppler expanded to 1.5 * 10
^{3}
Under abovementioned simulated environment, channel second footpath has maximum average gain.Simulation result as shown in Figure 4 and Figure 5, wherein method for synchronous of the present invention refers to that thick estimating step synchronously and thin estimating step synchronously adopt in the diagram all is method of estimation in the preferable scheme, as can be seen from Figure 4, the timing acquisition effect of tradition MLS and TR2 method is relatively poor, the acquisition probability upper limit only is respectively 0.05 and 0.17, because in most cases first directly power is less than other footpath, and conventional method only can be caught the due in the path with maximum gain; The time bias estimation that the present invention carries uses the mode of sliding window summation can capture the first directly time of advent as a rule, is limited to 0.78 on its acquisition probability, and performance boost is remarkable.As can be drawn from Figure 5, the frequency offset estimation accuracy of TR2, MLS and method for synchronous of the present invention all obtains obviously to promote successively.1 * 10
^{5}The mean square error level under, method of the present invention obtains the performance boost of 5dB than the TR2 method, obtains the performance boost of 3dB than the MLS method.
Those of ordinary skill in the art will appreciate that embodiment described here is in order to help reader understanding's principle of the present invention, should to be understood that protection scope of the present invention is not limited to such special statement and embodiment.Those of ordinary skill in the art can make various other various concrete distortion and combinations that do not break away from essence of the present invention according to these technology enlightenments disclosed by the invention, and these distortion and combination are still in protection scope of the present invention.
Claims (4)
1. an OFDM/OQAM system is characterized in that, the receiving terminal of described OFDM/OQAM system comprises:
Thick estimation module synchronously is used for the baseband receiving signals frame sequence r that estimation receives
_{1}(kT
_{S}) the frequency deviation estimated value
The compensate of frequency deviation module is used for the frequency deviation estimated value that thick estimation module is synchronously obtained
To the baseband receiving signals frame sequence r that receives
_{1}(kT
_{S}) carry out compensate of frequency deviation, obtain the receiving symbol frame sequence r behind the compensate of frequency deviation
_{2}(kT
_{S});
Thin estimation module synchronously is used for the r that estimates that the compensate of frequency deviation module obtains
_{2}(kT
_{S}) time inclined to one side estimated value
The partial compensation for the time module is used for the time inclined to one side estimated value that thin estimation module is synchronously obtained
The r that the compensate of frequency deviation module is obtained
_{2}(kT
_{S}) carry out partial compensation for the time, the receiving symbol frame sequence r when obtaining behind the compensate of frequency deviation
_{3}(kT
_{S});
Described thick estimation module synchronously is used for being achieved as follows process:
With baseband receiving signals frame sequence r
_{1}(kT
_{S}) and send consensus sequence s
_{TR}(kT
_{s}) to carry out length be (N
_{TR}ξ1/2) the second order slip computing crosscorrelation of N obtains a correlated series
Specifically be expressed as
Wherein
Right
The slip summation operation of carrying out the long D of fixed window obtains one and sequence
D＞τ wherein
_{Max}, choose and sequence,
Peak value inclined to one side test value when corresponding
As the time inclined to one side estimated value
Use again
Further estimate the frequency deviation estimated value
Wherein
Wherein, N is subcarrier number, N
_{TR}For frequency domain repeats frequency pilot sign number, N
_{g}For the nonzero sample of shaping filter function is counted T
_{s}Be the sampling period, τ
_{Max}Be the multipath channel maximum delay.
2. OFDM/OQAM according to claim 1 system is characterized in that, described thin estimation module synchronously is used for being achieved as follows process:
The compensate of frequency deviation step is obtained r
_{2}(kT
_{S}) and send consensus sequence s
_{TR}(kT
_{s}) to carry out length be (N
_{TR}ξ1/2) the second order slip computing crosscorrelation of N obtains a correlated series
Specifically be expressed as
Wherein
Right
The slip summation operation of carrying out the long D of fixed window obtains one and sequence
D＞τ wherein
_{Max}, choose and sequence,
Peak value inclined to one side test value when corresponding
As the time inclined to one side estimated value
3. OFDM/OQAM system time frequency method for synchronous comprises:
Thick estimating step synchronously is used for the baseband receiving signals frame sequence r that estimation receives
_{1}(kT
_{S}) the frequency deviation estimated value
The compensate of frequency deviation step is used for the frequency deviation estimated value that thick estimating step is synchronously obtained
To the baseband receiving signals frame sequence r that receives
_{1}(kT
_{S}) carry out compensate of frequency deviation, obtain the receiving symbol frame sequence r behind the compensate of frequency deviation
_{2}(kT
_{S});
Thin estimating step synchronously is used for the r that estimates that the compensate of frequency deviation step obtains
_{2}(kT
_{S}) time inclined to one side estimated value
The partial compensation for the time step is used for the time inclined to one side estimated value that thin estimating step is synchronously obtained
The r that the compensate of frequency deviation step is obtained
_{2}(kT
_{S}) carry out partial compensation for the time, the receiving symbol frame sequence r when obtaining behind the compensate of frequency deviation
_{3}(kT
_{S});
Described thick synchronous estimating step estimation procedure is as follows:
With baseband receiving signals frame sequence r
_{1}(kT
_{S}) and send consensus sequence s
_{TR}(kT
_{s}) to carry out length be (N
_{TR}ξ1/2) the second order slip computing crosscorrelation of N obtains a correlated series
Specifically be expressed as
Wherein
Right
The slip summation operation of carrying out the long D of fixed window obtains one and sequence
D＞τ wherein
_{Max}, choose and sequence
Peak value inclined to one side test value when corresponding
As the time inclined to one side estimated value
Use again
Further estimate the frequency deviation estimated value
Wherein
Wherein, N is subcarrier number, N
_{TR}For frequency domain repeats frequency pilot sign number, N
_{g}For the nonzero sample of shaping filter function is counted T
_{s}Be the sampling period, τ
_{Max}Be the multipath channel maximum delay.
4. timefrequency synchronization method according to claim 3 is characterized in that, described thin synchronous estimating step estimation procedure is as follows:
The compensate of frequency deviation step is obtained r
_{2}(kT
_{S}) and send consensus sequence s
_{TR}(kT
_{s}) to carry out length be (N
_{TR}ξ1/2) the second order slip computing crosscorrelation of N obtains a correlated series
Specifically be expressed as
Wherein
Right
The slip summation operation of carrying out the long D of fixed window obtains one and sequence
D＞τ wherein
_{Max}, choose and sequence,
Peak value inclined to one side test value when corresponding
As the time inclined to one side estimated value
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