CN100574302C - The synchronous method of a kind of OFDM integer frequency - Google Patents

Abstract

The invention discloses the synchronous method of a kind of OFDM integer frequency, this method at first is provided with equally spaced pilot tone in OFDM symbols transmitted, and the pilot frequency sequence among the continuous OFDM more than is spaced apart regularly, and the data on the pilot sub-carrier are set to difference in the adjacent OFDM symbol; The time of carrying out to the received signal afterwards is slightly synchronous, and it is synchronous to carry out the mark frequency deviation according to thick synchronous result of time, according to the synchronous result of frequency deviation received signal is transformed into frequency domain afterwards; And the difference between corresponding equally spaced pilot tone is relevant in the adjacent OFDM symbol of definite pilot transmitted signal, and in the frequency domain of described received signal in the adjacent OFDM symbol difference between corresponding equally spaced subcarrier relevant, it is synchronous to carry out integer frequency according to these two difference correlated results then.The present invention program need not be provided with targeting signal, can realize that integer frequency is synchronous.And the present invention program is also applicable to mobile multipath channel.

Description

The synchronous method of a kind of OFDM integer frequency

Technical field

The present invention relates to OFDM (OFDM) technology, relate to the synchronous method of a kind of OFDM integer frequency or rather.

Background technology

The OFDM technology is to utilize parallel transmission to improve a kind of mobile communication technology of communication data rate.The OFDM technology has many advantages such as availability of frequency spectrum height, anti-multipath interference and intersymbol interference, channel estimating and equilibrium realize easily, system's implementation complexity is low.The OFDM technology also is easy to combine with various multiple access technologies, thereby is generally believed it is indispensable core technology in the 4th third-generation mobile communication system.At present, the OFDM technology has been widely used in digital audio broadcasting (DAB), digital video broadcasting (DVB), ADSL (Asymmetric Digital Subscriber Line) (ADSL), wireless lan (wlan), wireless MAN (WMAN), Wireless Personal Network (WPAN) and the unauthorized metropolitan area network of the wireless high-speed many data communication systems such as (WHUMAN).In addition, determined to use the OFDM technology in 802.16 agreements, 802.20 mobile wide-band wire-less accessing systems that Institute of Electrical and Electric Engineers (IEEE) is being discussed at present also will adopt the OFDM technology.

Though the OFDM technology has above-mentioned plurality of advantages, and had application widely, also had a shortcoming that can not be ignored in this technology, just be to use the system of OFDM technology to need point-device Time and Frequency Synchronization, to guarantee the orthogonality between the subcarrier.Wherein, if the integer frequency bias synchronization failure then will cause the thorough mistake of final decode procedure.Therefore, the integer frequency bias in the ofdm system is a very important key technology in this system synchronously.

At present, United States Patent (USP) " 5,732,113 " discloses the method for a kind of OFDM time and Frequency Synchronization.This method is to insert the leading cell that structure is special at transmitting terminal, and this leading cell is by two OFDM symbols (symbol), and promptly SYN_A and SYN B constitute, and wherein, front and back two parts of SYN_A are identical.Receiving terminal utilizes this leading cell to finish the synchronously thick and mark frequency offset estimating of time of ofdm system in time domain, then the mark compensate of frequency deviation that estimates is fallen, and SYN_A and SYN_B transformed to frequency domain, utilize the correlation of SYN_A and SYN_B on the frequency domain to finish the estimation of integer frequency bias.

The time-frequency synchronization method that this patent provided can be realized Time and Frequency Synchronization apace, and have rational computation complexity, still, this scheme need add a leading cell at the front end of the information that will launch, obviously this can increase the expense of system, causes spectrum efficiency to descend.The length of burst block in system (burst) is than under the short situation, and this problem is particularly evident.

In addition, be " 200410042904.7 ", denomination of invention carry out matched filtering for " a kind of method of OFDM Time and Frequency Synchronization " proposed to utilize in the same OFDM symbol uniformly-spaced the difference of pilot sub-carrier to be correlated with to China's application number, finishes the synchronous implementation of integer frequency bias.This scheme specifically is at first to utilize to slide relevantly to the received signal with time window that circulating prefix-length equates, and it is slightly synchronous to rely on Cyclic Prefix in the OFDM symbol to carry out the time, to obtain the sync peaks phase information of received signal; And carry out the mark frequency offset estimating according to described sync peaks phase information, and revise according to the signal that this mark frequency offset estimating information butt joint is received, make only to have integer frequency bias in the revised received signal, then this received signal is transformed into frequency domain; Again the frequency-region signal that receives being carried out integer frequency bias afterwards estimates.Though this scheme need not can realize that integer frequency bias is synchronous by leading cell, this scheme only is fit to static channel.For mobile multipath channel, under time-variant multipath channel, each subcarrier in the same frame usually needs to experience different channel fadings, along with the carrying out of moving, multipath channel also can change, such as increasing new arriving at the path or present different decline feature etc., and channel becomes when quick and the decline of frequency domain selectivity can cause the rapid deterioration of channel performance, so this scheme is not suitable for mobile multipath channel.In addition under the situation of mobile channel; the integer frequency bias coarse synchronization method that is used to reduce amount of calculation in this patent usually can cause that the rough estimate to integer frequency bias departs from desired value far away; to cause the rapid increase and the final mistake of estimating of operand, this makes equally and can't use this scheme in mobile multipath channel.

Summary of the invention

In view of this, subject matter to be solved by this invention is to provide a kind of OFDM integer frequency synchronous method, so that ofdm system does not need leading cell can realize that integer frequency is synchronous.

For overcoming the above problems, technical scheme of the present invention is achieved in that the synchronous method of a kind of OFDM integer frequency, in the orthogonal frequency division multiplex OFDM symbol of emission, equally spaced pilot tone is set, and the pilot frequency sequence in the continuous OFDM symbol more than is spaced apart regularly, and the data on the pilot sub-carrier are set to difference in the adjacent OFDM symbol; This method further may further comprise the steps:

A. the time of carrying out to the received signal is slightly synchronous, and it is synchronous to carry out the mark frequency deviation according to thick synchronous result of time, afterwards according to the mark frequency deviation synchronously and the time slightly synchronous result received signal is transformed into frequency domain;

B. uniformly-spaced the difference between pilot tone is relevant in the adjacent OFDM symbol of definite pilot transmitted signal, and determine in the adjacent OFDM symbol of the pairing frequency-region signal of described received signal, the difference of the subcarrier identical with the set pilot frequency locations pattern of transmitting terminal is relevant, and it is synchronous to carry out integer frequency according to these two difference correlated results then.

Among the described step b, describedly carry out integer frequency according to two difference correlated results and be synchronously:

To in the adjacent OFDM symbol of pilot transmitted signal uniformly-spaced the difference correlated results between pilot tone carry out conjugation, and with in every in this conjugate sequence adjacent OFDM symbol with pairing frequency-region signal to received signal, the subcarrier identical with the set pilot frequency locations pattern of transmitting terminal the respective items of difference correlated results multiply each other, in transmitting terminal and receiving terminal crystal oscillator frequency deviation region, determine maximum product value, determine integer frequency bias according to the sequence of the equally spaced pilot tone in the pairing received signal of this max product value.

This method may further include: an above OFDM symbol that begins most that is comprised in each the OFDM frame that will launch identifies as frame head, and equally spaced pilot frequency sequence is set to be different from the value of equally spaced pilot frequency sequence in the follow-up OFDM symbol in the described OFDM symbol;

Among the step b, uniformly-spaced the difference between pilot tone is relevant in the adjacent OFDM symbol of described definite pilot transmitted signal is: obtain two or more continuous OFDM symbols as the frame head sign, and determine that according to the OFDM symbol that is obtained uniformly-spaced the difference between pilot tone is relevant in the adjacent OFDM symbol of pilot transmitted signal;

Among the step b, in the adjacent OFDM symbol of the pairing frequency-region signal of described definite received signal, the difference of the subcarrier identical with the set pilot frequency locations pattern of transmitting terminal is relevant to be: obtain two or more continuous OFDM symbols, and determine in the adjacent OFDM symbol of the pairing frequency-region signal of received signal that according to the OFDM symbol that is obtained the difference of the subcarrier identical with the set pilot frequency locations pattern of transmitting terminal is relevant;

Among the step b, describedly carry out integer frequency according to two difference correlated results and be synchronously:

To in the adjacent OFDM symbol of pilot transmitted signal uniformly-spaced the difference correlated results between pilot tone carry out conjugation, and in the sequence that this conjugation is obtained every adjacent OFDM symbol with the pairing frequency-region signal of received signal, the respective items of the difference correlated results of the subcarrier identical with the set pilot frequency locations pattern of transmitting terminal multiplies each other, determine the max product value in transmitting terminal and receiving terminal crystal oscillator frequency deviation region, and the average absolute of all product values;

And whether the ratio of judging the absolute value of this product value and this mean value greater than pre-set threshold, if, then determine integer frequency bias success synchronously, determine the frame synchronization success simultaneously; Otherwise it is unsuccessful to determine that integer frequency bias reaches frame synchronization synchronously.

Described step b definite integer frequency bias reach synchronously frame synchronization unsuccessful after, further comprise: two or more continuous OFDM symbols that obtain received signal again, and determine in the adjacent OFDM symbol of the pairing frequency-region signal of received signal according to described OFDM symbol, the difference of the subcarrier identical with the set pilot frequency locations pattern of transmitting terminal is relevant, carries out again afterwards carrying out the synchronous operation of integer frequency according to two difference correlated results among the step b.

Among the described step a, the described time of carrying out to the received signal slightly is synchronously: it is relevant to utilize the equal time window of circulating prefix-length that is adopted with system to slide to the received signal, and the described Cyclic Prefix that adopts is the Cyclic Prefix in the described OFDM symbol; And it is slightly synchronous to carry out the time according to the Cyclic Prefix that is adopted, and obtains the sync peaks phase information of received signal.

The Cyclic Prefix that is adopted can be one;

Then the length of the Cyclic Prefix that is adopted during more than or equal to system applies the time delay expansion and signal to noise ratio is determined when counting, the time window that described step a utilizes is: the time window with the equal in length of the described Cyclic Prefix that adopts;

The length of the Cyclic Prefix that is adopted during less than system applies the time delay expansion and during the determined circulating prefix-length of signal to noise ratio, the time window that described step a utilizes is: with the time window of the equal in length of the Cyclic Prefix that is adopted, and be the interval with the length of OFDM symbol and the circulating prefix-length sum that is adopted between each time window more than one.

The Cyclic Prefix that is adopted can also be for more than one;

Among the step a, the circulating prefix-length that described utilization and system are adopted equate time window slide to the received signal and relevantly be: it is relevant that at least one OFDM symbol is slided, and the slip correlated results is carried out normalization measure;

Among the step a, it is described that to carry out the time according to the Cyclic Prefix that is adopted slightly synchronous, the sync peaks phase information of obtaining received signal is: determine the maximum of the ratio of the absolute value of slip correlated results and normalization metric, with the pairing time point of this maximum as time synchronized constantly.

Uniformly-spaced the difference between pilot tone is relevant in the described adjacent OFDM symbol of determining the pilot transmitted signal according to the OFDM symbol that is obtained comprises:

B1. obtain in transmitting more than one the pilot frequency sequence of OFDM symbol continuously, the conjugate multiplication of same position pilot tone in each pilot tone in each pilot frequency sequence and back one pilot frequency sequence, obtain product sequence, from each product sequence that obtains, take out the element of high order end more successively, element in all product sequence all is removed, and described element is lined up a collating sequence;

Describedly determine in the adjacent OFDM symbol of the pairing frequency-region signal of received signal relevant the comprising of difference of the subcarrier identical with the set pilot frequency locations pattern of transmitting terminal according to the OFDM symbol that is obtained:

It is identical and have a frequency-region signal sequence identical with transmitting terminal pilot frequency locations pattern to obtain the number of pilot sequences of being obtained with step b1 from received signal, afterwards the conjugate multiplication of the subcarrier of relevant position in each subcarrier in each frequency-region signal sequence and the back one frequency-region signal sequence, from each product sequence that obtains, take out the element of high order end more successively, element in all product sequence all is removed, and described element is lined up a collating sequence.

Described transmitting terminal is the base station, and receiving terminal is a travelling carriage;

This method further comprises: different pilot frequency sequences is sent in the base station that different districts is set;

Travelling carriage is determined different districts signal of base station power according to the range value of the frequency domain matched filtering of being signaled in the different districts base station, and determines the merging of selecting that the result selects cell base station or carries out the cell base station pilot frequency sequence according to this.

Carrying out integer frequency according to two difference correlated results among the described step b is synchronously: carry out the frequency domain matched filtering or slide relevant according to two difference correlated results.

The present invention program is by being provided with OFDM symbols transmitted, and by equally spaced pilot tone in the adjacent OFDM symbol of determining to transmit, and in the frequency domain of received signal in the adjacent OFDM symbol, the difference that has between the subcarrier with transmitting terminal same intervals pattern is relevant, wherein, this interval mode comprises pilot interval pattern in the same OFDM symbol and the pilot interval pattern between adjacent OFDM symbol, and then carry out the frequency domain matched filtering or slide relevant according to these two difference correlated results, thereby make and leading cell need be set in frame, the integer frequency that can realize OFDM is synchronous, thereby has significantly reduced overhead.

Since the present invention program be according to transmit and a plurality of adjacent OFDM channels of received signal to carry out difference relevant, and then carry out the frequency domain matched filtering, so the present invention program is equally applicable to mobile multipath channel according to the difference correlated results.According to emulation, be that the time slightly is offset 15 chips synchronously forward under the typical urban channel (TU channel) of 3km/h, 60km/h, 120km/h in 0dB, translational speed, it is synchronous that wrong integer frequency bias does not all appear in emulation 200000 frames.

The present invention program identifies as frame head by an above OFDM symbol that begins most in each OFDM frame of emission, and the sequence of equally spaced pilot tone is set to be different from the value of the sequence of equally spaced pilot tone in the follow-up OFDM symbol in these OFDM symbols, also when realizing that integer frequency is synchronous, realized frame synchronization.In addition, the present invention program is when slightly making a mistake synchronously to the time of OFDM symbol before, if the thick success synchronously of the time of several afterwards OFDM symbols then still can be finished frame synchronization by the synchronous method of integer frequency of the present invention, improved the probability of success of frame synchronization greatly.Certainly, precondition is that the recipient has enough memory spaces to deposit the information of continuous a plurality of OFDM symbol sebolic addressings.

In addition, can also be set to send different pilot frequency sequences by the base station of different districts, make the recipient, be the power that travelling carriage can be determined the signal that sends from the base station of different districts by the range value of frequency deviation matched filtering, thereby according to strong and weak soft handover, merging and other corresponding work of determining the minizone of this signal.

Description of drawings

Fig. 1 is that the pilot tone of OFDM symbol in the embodiment of the invention is arranged schematic diagram;

Fig. 2 is the present invention program's a processing procedure schematic diagram.

Embodiment

Core concept of the present invention is: the time of at first carrying out to the received signal is slightly synchronous; It is synchronous to carry out the mark frequency deviation according to thick synchronous result of time then, according to the synchronous result of mark frequency deviation received signal is transformed into frequency domain again; It is synchronous to carry out integer frequency with the information that knows of frequency domain and the signal frequency-domain information that is received in frequency domain, and such as carrying out matched filtering or slide relevantly, finding match peak, and it is synchronous to finish integer frequency bias according to this peak value.

Below in conjunction with drawings and the specific embodiments the present invention program is described in further detail.

The present invention program at first will introduce equally spaced pilot tone in the OFDM symbol, and the pilot frequency sequence in continuous several OFDM symbols is spaced apart regularly.Certainly, the interval rule of the equally spaced pilot tone between all OFDM symbols also should be identical, that is to say, the sequence of the equally spaced pilot tone in the several successive OFDM symbol is set to equidistant dislocation.

Such as, can in same OFDM symbol, a pilot tone be set every interval N subcarrier, and with M the subcarrier that be set to of equally spaced pilot tone in the adjacent OFDM symbol, synchronous for determining correct integer frequency bias, the data in adjacent OFDM symbol on the pilot sub-carrier should be inequality.Therefore, for continuous 6 OFDM symbols, if N is 12, M is 4, and the pilot tone of then such OFDM symbol is arranged as shown in Figure 1.

Based on above-mentioned setting, the present invention program's specific implementation process as shown in Figure 2, corresponding following steps:

Step 201, time are slightly synchronous.

This step specifically is that to utilize the time window that equates with circulating prefix-length to slide to received signal relevant, and it is slightly synchronous to utilize the interior Cyclic Prefix of OFDM symbol to carry out the time, to obtain the sync peaks phase information of the signal that receives.Wherein, the Cyclic Prefix that is adopted can be to have only one, also can be a plurality of.

If the Cyclic Prefix that is adopted has only one, it is slightly synchronous then can to adopt present existing processing method to carry out the time.Such as, in the long ofdm system of Cyclic Prefix such as IEEE802.16a OFDMA pattern, the length of Cyclic Prefix during more than or equal to system applies the time delay expansion and signal to noise ratio is determined counts, during such as 64, adopt a time window that equates with circulating prefix-length can obtain good time synchronized performance.

Cyclic Prefix in ofdm system is shorter, such as the length of Cyclic Prefix less than the time delay expansion and signal to noise ratio is determined when counting, owing to be the interval between these time windows with OFDM symbol lengths and circulating prefix-length sum, therefore adopt more than one and to slide relevantly to the received signal, can obtain good time synchronized performance equally with the isometric time window of Cyclic Prefix.

Thick synchronous for the time of being undertaken by a plurality of Cyclic Prefix, with the time of being undertaken by three Cyclic Prefix slightly be example synchronously, it can utilize following formula (1) the relevant P (d) that obtains sliding, and utilize following formula (2) that the P (d) that obtains is carried out normalization tolerance, obtain the tolerance R (d) of energy, ask the ratio of P (d) and R (d) again $M\left(d\right)=\frac{\left|P\left(d\right)\right|}{R\left(d\right)},$ With the pairing d of the maximum of this ratio as the maximum estimated value

And will

As thick synchronization point of time.

$P\left(d\right)=\underset{m=0}{\overset{m=\mathrm{GI}-1}{\mathrm{\Σ}}}\left(r_{d+m}^{*}{r}_{d+m+N}\right)+\underset{m=0}{\overset{m=\mathrm{GI}-1}{\mathrm{\Σ}}}\left(r_{d+m+N+\mathrm{GI}}^{*}{r}_{d+m+2N+\mathrm{GI}}\right)+\underset{m=0}{\overset{m=\mathrm{GI}-1}{\mathrm{\Σ}}}\left(r_{d+m+2(N+\mathrm{GI})}^{*}{r}_{d+m+3N+2\mathrm{GI}}\right)$ Formula (1)

$R\left(d\right)=\frac{1}{2}\left[\begin{array}{c}\underset{m=0}{\overset{m=\mathrm{GI}-1}{\mathrm{\Σ}}}(r_{d+m}^{*}{r}_{d+m}+r_{d+m+N}^{*}{r}_{d+m+N})+\underset{m=0}{\overset{m=\mathrm{GI}-1}{\mathrm{\Σ}}}(r_{d+m+N+\mathrm{GI}}^{*}{r}_{d+m+2N+\mathrm{GI}}+r_{d+m+2N+\mathrm{GI}}^{*}{r}_{d+m+2N+\mathrm{GI}})\\ +\underset{m=0}{\overset{m=\mathrm{GI}-1}{\mathrm{\Σ}}}(r_{d+m+2(N+\mathrm{GI})}^{*}{r}_{d+m+2(N+\mathrm{GI})}+r_{d+m+3N+2\mathrm{GI}}^{*}{r}_{d+m+3N+2\mathrm{GI}})\end{array}\right]$ Formula (2)

Wherein, r is the signal that receives, and d is a time point, and GI is the length of Cyclic Prefix, and N is the length of OFDM symbol, so r following is designated as the time.

Step 202, mark frequency offset estimating.

This step is to utilize the phase information of the sync peaks position that the time slightly obtains synchronously to carry out the mark frequency offset estimating.Specifically can pass through Δ f ₁=Angle (P (d))/N calculates, and wherein, N is the length of OFDM symbol.

Step 203, mark compensate of frequency deviation.

This step specifically is to utilize the mark frequency deviation information that estimates to revise to the received signal, makes only to have integer frequency bias and mark residual frequency departure in the revised received signal.

Step 204, time-frequency conversion (FFT).

The result that this step specifically is synchronous according to the mark frequency deviation and the time is slightly synchronous arrives frequency domain with the conversion of signals that receives, and estimates to carry out integer frequency bias.

Step 205, the OFDM symbol of frequency domain is carried out integer frequency bias estimate.

For step 205, difference in a plurality of known adjacent OFDM symbol of the definite pilot transmitted signal of needs between equally spaced pilot tone is relevant, and in a plurality of OFDM symbols of the pairing frequency-region signal of signal that receives, the difference of the subcarrier identical with the set pilot frequency locations pattern of transmitting terminal is relevant, then these two difference correlated results are carried out the frequency domain matched filtering, thus realize to integer frequency bias synchronously.

Specifically, when the difference in a plurality of known adjacent OFDM symbol of determining the pilot transmitted signal between equally spaced pilot tone is relevant, at first to obtain the known pilot sequence of several successive OFDM symbol, and carry out the relevant of two adjacent pilot frequencies sequences, promptly the conjugate multiplication of the pilot tone of relevant position in each pilot tone in each pilot frequency sequence and back one pilot frequency sequence, the all sequences that product is obtained is arranged in order again, thereby obtains a sequence after the merging.This union operation is: sequentially the high order end from the product sequence that obtains takes out elements corresponding in turn, and all elements in all product sequence all has been removed, and the order of again these elements being pressed when taking out forms a sequence afterwards.

Such as, determined that at first the known pilot subcarrier sequence in continuous four OFDM symbols is respectively: P ₁=[p ₁₁p ₁₂P _1n], P ₂=[p ₂₁p ₂₂P _2n], P ₃=[p ₃₁p ₃₂P _3n] and P ₄=[p ₄₁p ₄₂P _4n].Obtain pilot frequency sequence relevant of two adjacent OFDM symbol by product, promptly obtain $P_{12}=\left[\begin{array}{cccc}{p}_{11}{p}_{21}^{*}& p_{12}{p}_{22}^{*}& \·\·\·& p_{1,n-1}{p}_{2n-1}^{*}\end{array}\right],$ $P_{23}=\left[\begin{array}{cccc}{p}_{21}{p}_{31}^{*}& p_{22}{p}_{32}^{*}& \·\·\·& p_{2,n-1}{p}_{3n-1}^{*}\end{array}\right]$ And $P_{34}=\left[\begin{array}{cccc}{p}_{31}{p}_{41}^{*}& p_{32}{p}_{42}^{*}& \·\·\·& p_{3,n-1}{p}_{4n-1}^{*}\end{array}\right],$ Upper right mark wherein ^*Conjugation is got in expression.Again with sequence P ₁₂, P ₂₃And P ₃₄Merge into a sequence P, obtain:

$P=\left[\begin{array}{cccccccccc}{p}_{11}{p}_{21}^{*}& p_{21}{p}_{31}^{*}& p_{31}{p}_{41}^{*}& p_{12}{p}_{22}^{*}& p_{22}{p}_{31}^{*}& p_{32}{p}_{42}^{*}& \·\·\·& p_{1,.n-1}{p}_{2n-1}^{*}& p_{2,n-1}{p}_{3n-1}^{*}& p_{3,n-1}{p}_{4n-1}^{*}\end{array}\right]$

Four OFDM symbols have been used owing to the difference of doing at the pilot signal of transmitting terminal is relevant, therefore this step has difference between the subcarrier of transmitting terminal pilot interval pattern when relevant in a plurality of OFDM symbols of determining the pairing frequency-region signal of received signal, and finishing integer frequency bias with the pilot frequency sequence that uses four OFDM symbols is example synchronously equally.Specifically, the frequency-region signal sequence of continuous four the OFDM symbols in the received signal that obtains of obtaining step 204 at first, and it is labeled as R respectively ₁=[r ₁₁r ₁₂R _1N], R ₂=[r ₂₁r ₂₂R _2N], R ₃=[r ₃₁r ₃₂R _3N] and R ₄=[r ₄₁r ₄₂R _4N].And then the position of the equally spaced pilot tone that in same OFDM symbol and adjacent OFDM symbol, is provided with according to transmitting terminal relation, it also is the set pilot frequency locations pattern of transmitting terminal, same position from these several frequency-region signal sequences is obtained corresponding sequence respectively, such as, obtain: (R ₁') _k=[(r ₁₁') _k(r ₁₂') _k(r _1n') _k], (R ₂') _k=[(r ₂₁') _k(r ₂₂') _k(r _2n') _k], (R ₃') _k=[(r ₃₁') _k(r ₃₂') _k(r _3n') _k] and ( _R4') _k=[(r ₄₁') _k(r ₄₂') _k(r _4n') _k],

Wherein, k represents the sequence number of current selected sequence.

Obviously, resulting sequence (R ₁') _k, (R ₂') _k, (R ₃') _kAnd (R ₄') _kFour OFDM symbols of arrangement and emission side in the position of sequence of equally spaced pilot tone corresponding, be a kind of sliding relation.

Afterwards again to (R ₁') _k, (R ₂') _k, (R ₃') _kAnd (R ₄') _kThese several sequences are carried out the relevant of two adjacent frequency-region signal sequences, promptly the conjugate multiplication of the subcarrier of relevant position in each subcarrier in each frequency-region signal sequence and the back one frequency-region signal sequence, the all sequences that product is obtained is arranged in order again, thereby obtains a sequence after the merging.The processing procedure that difference in a plurality of adjacent OFDM symbol of this processing procedure and definite transmitting terminal between equally spaced pilot tone is relevant is identical, therefore is not described in detail.Sequence after the merging that obtains by this processing is:

${\left(R^{\′}\right)}_k=\left[\begin{array}{c}\begin{array}{cccccc}{\left(r_{11}^{\′}\right)}_k{\left(r_{21}^{\′}\right)}_k^{*}& {\left(r_{21}^{\′}\right)}_k{\left(r_{31}^{\′}\right)}_k^{*}& {\left(r_{31}^{\′}\right)}_k{\left(r_{41}^{\′}\right)}_k^{*}& {\left(r_{12}^{\′}\right)}_k{\left(r_{22}^{\′}\right)}_k^{*}& {\left(r_{22}^{\′}\right)}_k{\left(r_{32}^{\′}\right)}_k^{*}& {\left(r_{33}^{\′}\right)}_k{\left(r_{43}^{\′}\right)}_k^{*}\end{array}\\ \begin{array}{cccc}...& {\left(r_{1,n-1}^{\′}\right)}_k{\left(r_{2,n-1}^{\′}\right)}_k^{*}& {\left(r_{2,n-1}^{\′}\right)}_k{\left(r_{3,n-1}^{\′}\right)}_k^{*}& {\left(r_{3,n-1}^{\′}\right)}_k{\left(r_{4,n-1}^{\′}\right)}_k^{*}\end{array}\end{array}\right].$

Obtaining P and (R ') _kAfter these two sequences, again these two difference correlated results are carried out the frequency domain matched filtering, be about to (R ') _kMultiplying each other with the respective items of the conjugation of P, and by adjusting the value of k, in the possible scope of transmitting terminal and receiving terminal crystal oscillator frequency deviation, also is in the possible scope of integer frequency bias, finds out maximum product value, determines corresponding sequence (R according to the pairing k of this product value then ₁₂') _k, (R ₂₃') _k(R ₃₄') _k, should (R ₁₂') _k, (R ₂₃') _k(R ₃₄') _kBe corresponding equally spaced pilot frequency sequence, after having determined the k value, promptly be equivalent to determine the pilot frequency locations in the pilot frequency sequence, get final product the position of specified data subcarrier in view of the above, thereby can find the position of integer frequency bias, therefore, can determine integer frequency bias according to this pilot frequency sequence and k value uniformly-spaced.

Can realize purpose of the present invention by said process.

In addition, need to prove,,, can finally realize integer frequency bias by such scheme no matter the n value is much if the equally spaced pilot tone in continuous n the OFDM symbol is arranged in order by rule.Certainly, want to realize purpose of the present invention, should merge by two sequences at least, to obtain sequence P and (R ') _kObviously, the sequence that is used to merge is many more, and then the peak value that obtains of matched filtering is big more.Certainly,, then can increase operand and delay, so can be identified for the number of the sequence that merges as required if the sequence that is used to merge is too many.

In the said process, step 205 is to obtain sequence P and (R ') by three sequences are merged _k, this is only for OFDM symbol pilot tone arrangement scheme shown in Figure 1.Because in the OFDM symbol shown in Figure 1, equally spaced pilot tone in first three OFDM symbol is arranged by rule, for the 4th to the 6th OFDM symbol, then repeated the arrangement regulation of first three again, that is to say, can determine the sequence of corresponding equally spaced pilot tone according to three OFDM symbols.

The present invention program can also be further in beginning S OFDM symbol of each OFDM frame of transmitting terminal the value of the sequence of equally spaced pilot tone be set to differently with follow-up OFDM symbol, thick synchronously, mark frequency offset estimating of the time of carrying out successively afterwards, mark compensate of frequency deviation, FFT and integer frequency bias are estimated.Wherein, when carrying out the integer frequency bias estimation, the implementation that utilizes above-mentioned steps 205 to mention equally.

Because it is different that beginning S OFDM symbol of OFDM frame and the value of the sequence of the equally spaced pilot tone of follow-up OFDM symbol exist, so achieve frame is synchronous on this basis, at this moment, this set S OFDM symbol identifies as frame head.This be because: the sequence that different uniformly-spaced pilot tones is set in beginning S OFDM symbol of each OFDM frame is used to identify frame head, and matched filtering has only and identically could mate and produce peak value, therefore, if the matched filtering of back operation can produce peak value, then frame head has been found in explanation.

For achieve frame synchronous, carry out matched filtering or slide relevant find the maximum of correlation after, whether the ratio of average of absolute value that can also further judge this peaked absolute value and correlated results sequence is greater than a pre-set threshold, if, then show integer frequency bias synchronously and the frame synchronization success, so original position that can locating frame.If less than this threshold value, show that then integer frequency bias is synchronous and frame synchronization is unsuccessful.

Under the situation of this ratio,, can also carry out integer frequency bias by the 2nd to S+1 OFDM symbol and estimate, and carry out the comparison of above-mentioned ratio and threshold value for realizing the synchronous and frame synchronization of integer frequency bias less than threshold value.And the like, can also carry out integer frequency bias to the 3rd to S+2 OFDM symbol and estimate.Certainly, synchronous for achieve frame, can only carry out integer frequency bias to 2S-1 OFDM symbol by S at most and estimate, because carry out must having one to can be used as the frame head sign at least in the OFDM symbol that integer frequency bias estimates, otherwise just can't achieve frame synchronous.

In addition, if by the sub-district is provided with, make the base station in the different districts send different pilot frequency sequences, and the recipient adopts scheme provided by the present invention to carry out the integer frequency bias estimation, then the recipient is behind the range value of determining the frequency domain matched filtering of signaling in each base station, can determine the signal power of respective base station by the size that compares these range values, thereby make the recipient can finish the switching of minizone.

The above only is the present invention program's preferred embodiment, not in order to limit protection scope of the present invention.

Claims (10)

1, the synchronous method of a kind of OFDM integer frequency, it is characterized in that, in the orthogonal frequency division multiplex OFDM symbol of emission, equally spaced pilot tone is set, and the pilot frequency sequence in the continuous OFDM symbol more than is spaced apart regularly, and the data on the pilot sub-carrier are set to difference in the adjacent OFDM symbol; This method further may further comprise the steps:

A. the time of carrying out to the received signal is slightly synchronous, and it is synchronous to carry out the mark frequency deviation according to thick synchronous result of time, afterwards according to the mark frequency deviation synchronously and the time slightly synchronous result received signal is transformed into frequency domain;

B. uniformly-spaced the difference between pilot tone is relevant in the adjacent OFDM symbol of definite pilot transmitted signal, and determine in the adjacent OFDM symbol of the pairing frequency-region signal of described received signal, the difference of the subcarrier identical with the set pilot frequency locations pattern of transmitting terminal is relevant, and it is synchronous to carry out integer frequency according to these two difference correlated results then.

2, method according to claim 1 is characterized in that among the described step b, describedly carries out integer frequency according to two difference correlated results and is synchronously:

To in the adjacent OFDM symbol of pilot transmitted signal uniformly-spaced the difference correlated results between pilot tone carry out conjugation, and with in every in this conjugate sequence adjacent OFDM symbol with the pairing frequency-region signal of received signal, the respective items of the difference correlated results of the subcarrier identical with the set pilot frequency locations pattern of transmitting terminal multiplies each other, in transmitting terminal and receiving terminal crystal oscillator frequency deviation region, determine maximum product value, determine integer frequency bias according to the sequence of the equally spaced pilot tone in the pairing received signal of this max product value.

3, method according to claim 1, it is characterized in that, this method further comprises: an above OFDM symbol that begins most that is comprised in each the OFDM frame that will launch identifies as frame head, and equally spaced pilot frequency sequence is set to be different from the value of equally spaced pilot frequency sequence in the follow-up OFDM symbol in the described OFDM symbol;

Among the step b, uniformly-spaced the difference between pilot tone is relevant in the adjacent OFDM symbol of described definite pilot transmitted signal is: obtain more than two the continuous OFDM symbol as the frame head sign, and determine that according to the OFDM symbol that is obtained uniformly-spaced the difference between pilot tone is relevant in the adjacent OFDM symbol of pilot transmitted signal;

Among the step b, in the adjacent OFDM symbol of the pairing frequency-region signal of described definite received signal, the difference of the subcarrier identical with the set pilot frequency locations pattern of transmitting terminal is relevant to be: obtain OFDM symbol continuous more than two, and determine in the adjacent OFDM symbol of the pairing frequency-region signal of received signal that according to the OFDM symbol that is obtained the difference of the subcarrier identical with the set pilot frequency locations pattern of transmitting terminal is relevant;

Among the step b, describedly carry out integer frequency according to two difference correlated results and be synchronously:

To in the adjacent OFDM symbol of pilot transmitted signal uniformly-spaced the difference correlated results between pilot tone carry out conjugation, and in the sequence that this conjugation is obtained every adjacent OFDM symbol with the pairing frequency-region signal of received signal, the respective items of the difference correlated results of the subcarrier identical with the set pilot frequency locations pattern of transmitting terminal multiplies each other, determine the max product value in transmitting terminal and receiving terminal crystal oscillator frequency deviation region, and the average absolute of all product values;

And whether the ratio of judging the absolute value of this product value and this mean value greater than pre-set threshold, if, then determine integer frequency bias success synchronously, determine the frame synchronization success simultaneously; Otherwise it is unsuccessful to determine that integer frequency bias reaches frame synchronization synchronously.

4, method according to claim 3, it is characterized in that, described step b definite integer frequency bias reach synchronously frame synchronization unsuccessful after, further comprise: the continuous OFDM symbol more than two that obtains received signal again, and determine in the adjacent OFDM symbol of the pairing frequency-region signal of received signal according to described OFDM symbol, the difference of the subcarrier identical with the set pilot frequency locations pattern of transmitting terminal is relevant, carries out again afterwards carrying out the synchronous operation of integer frequency according to two difference correlated results among the step b.

5, according to any described method in the claim 1 to 4, it is characterized in that among the described step a, the described time of carrying out to the received signal slightly is synchronously: it is relevant to utilize the equal time window of circulating prefix-length that is adopted with system to slide to the received signal, and the described Cyclic Prefix that adopts is the Cyclic Prefix in the described OFDM symbol; And it is slightly synchronous to carry out the time according to the Cyclic Prefix that is adopted, and obtains the sync peaks phase information of received signal.

6, method according to claim 5 is characterized in that, the Cyclic Prefix that is adopted is one;

The length of the Cyclic Prefix that is adopted during more than or equal to system applies the time delay expansion and during the determined circulating prefix-length of signal to noise ratio, the time window that described step a utilizes is: the time window with the equal in length of the described Cyclic Prefix that adopts;

The length of the Cyclic Prefix that is adopted during less than system applies the time delay expansion and during the determined circulating prefix-length of signal to noise ratio, the time window that described step a utilizes is: with the time window of the equal in length of the Cyclic Prefix that is adopted, and be the interval with the length of OFDM symbol and the circulating prefix-length sum that is adopted between each time window more than one.

7, method according to claim 5 is characterized in that the Cyclic Prefix that is adopted is more than one;

Among the step a, the time window that the circulating prefix-length that described utilization and system are adopted equates slides to the received signal and relevantly is: it is relevant that at least one OFDM symbol is slided, and the slip correlated results is carried out normalization measure;

Among the step a, it is described that to carry out the time according to the Cyclic Prefix that is adopted slightly synchronous, the sync peaks phase information of obtaining received signal is: determine the maximum of the ratio of the absolute value of slip correlated results and normalization metric, with the pairing time point of this maximum as time synchronized constantly.

8,, it is characterized in that uniformly-spaced the difference between pilot tone is relevant in the described adjacent OFDM symbol of determining the pilot transmitted signal according to the OFDM symbol that is obtained to comprise according to claim 3 or 4 described methods:

B1. obtain in transmitting more than one the pilot frequency sequence of OFDM symbol continuously, the conjugate multiplication of same position pilot tone in each pilot tone in each pilot frequency sequence and back one pilot frequency sequence, obtain product sequence, from each product sequence that obtains, take out the element of high order end more successively, element in all product sequence all is removed, and described element is lined up a collating sequence;

Describedly determine in the adjacent OFDM symbol of the pairing frequency-region signal of received signal relevant the comprising of difference of the subcarrier identical with the set pilot frequency locations pattern of transmitting terminal according to the OFDM symbol that is obtained:

It is identical and have a frequency-region signal sequence identical with transmitting terminal pilot frequency locations pattern to obtain the number of pilot sequences of being obtained with step b1 from received signal, afterwards the conjugate multiplication of the subcarrier of relevant position in each subcarrier in each frequency-region signal sequence and the back one frequency-region signal sequence, from each product sequence that obtains, take out the element of high order end more successively, element in all product sequence all is removed, and described element is lined up a collating sequence.

9, according to any described method in the claim 1 to 4, it is characterized in that described transmitting terminal is the base station, receiving terminal is a travelling carriage;

This method further comprises: different pilot frequency sequences is sent in the base station that different districts is set;

Travelling carriage is determined different districts signal of base station power according to the range value of the frequency domain matched filtering of being signaled in the different districts base station, and determines the selection merging that the result selects cell base station or carries out the cell base station pilot frequency sequence according to this.

10, method according to claim 1 is characterized in that, carries out integer frequency according to two difference correlated results among the described step b to be synchronously: carry out the frequency domain matched filtering or slide relevant according to two difference correlated results.

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