CN100562002C - Protection fill method and communication system thereof at interval in a kind of orthogonal FDM modulation system - Google Patents

Abstract

The invention discloses protection fill method and communication system thereof at interval in a kind of orthogonal FDM modulation system, belong to digital information transmission technical field.Described method comprises: sequence length selection, sequence selection, sequence interstitital texture are selected, channel estimation method, use broad sense Legendre sequence or its inverse discrete Fourier transformer inverse-discrete as training sequence in above-mentioned steps.The broad sense Legendre sequence comprises Legendre symbol, Legendre sequence, expansion Legendre sequence.Use broad sense Legendre sequence or its inverse Fourier transform as the advantage of training sequence to be, broad sense Legendre sequence length is selected more, can more complete filling protect at interval; Frequency domain is smooth; Time domain two-value or three values, and have symmetry, time domain is handled easily; Frequency domain two-value or three values, the channel estimating computational complexity is low, the estimated accuracy height.

Description

Protection fill method and communication system thereof at interval in a kind of orthogonal FDM modulation system

Technical field

The invention belongs to digital information transmission technical field; be particularly related to OFDM (Orthogonal FrequencyDivision Multiplexing; OFDM) multicarrier system (Multi Carrier; MC) or single carrier (Single Carrier; SC) (Training Sequence is TS) as protecting the communication system of filling at interval based on training sequence in the system.

Background technology

The core of communication system is how to improve efficiency of transmission and reliability in limited bandwidth.Therefore, in Digital Television or computer system, the payload of each transmission frame or valid data part should account for the big as far as possible part of transmission frame, so that improve the efficiency of transmission of system.Simultaneously, system should be able to discern and compensate the characteristic variations of transmission channel, so that realize reliable transmission.Realize above-mentioned high efficiency and high reliability, system want can be from the signal specific of Channel Transmission recovered clock, the reinsertion of carrier and the estimation characteristic of channel, and this signal is also as the protection of transmission signals at interval and frame synchronization.

Single carrier and multicarrier modulation system are under wireless multi-path channel in addition, can produce frequency selective fading, be intersymbol interference (Inter Symbol Interference, ISI), to with the data block for the unit system for transmitting can cause inter-block-interference (InterBlock Interference, IBI).A kind of method that anti-multipath is disturbed be between transmission data block, add protection at interval (GuardInterval, GI).Usually protection length at interval is not less than the maximum multipath time-delay of channel, and then the data block between the protection does not at interval have inter-block-interference.Protection fill method at interval has multiple: and Cyclic Prefix (Cyclic Prefix, CP), zero padding (Zero Padding, ZP).The ofdm system frame structure that Cyclic Prefix is filled as shown in Figure 1, DFT (discrete Fourier transform (DFT)) (perhaps FFT, fast fourier algorithm) piece A2 is positioned at after the Cyclic Prefix section A1, Cyclic Prefix as the protection of DFT at interval.The ofdm system frame result of zero padding as shown in Figure 2, the zero padding section is followed in DFT piece back, this zero padding section as the protection of DFT piece at interval.Referring to document [Muquet B, Wang Z, Giannakis G.B, Courville M.de, and Duhamel P, CyclicPrefixing or Zero Padding for Wireless Multicarrier Transmissions, IEEE Trans.onCommunications, 2002,50 (12): 2136-2148].CP-OFDM (ofdm system of Cyclic Prefix) has obtained extensive use at present, as digital audio broadcasting (Digital Audio Broadcasting, DAB), digital video broadcast-terrestrial (Terestrial Digital Video Broadcasting, DVB-T), IEEE 802.11a, HIPERLAN/2 WLAN standard etc. have all used CP-OFDM.

The Chinese invention patent of Tsing-Hua University's application [protection fill method at interval in the orthogonal FDM modulation system, application number 01124144.6] has proposed the third OFDM frame format.As shown in Figure 3, DFT piece back is followed pseudo random sequence (Pseudorandom Noise PN) is filled, and this PN filled section as the protection of DFT piece at interval.This structure be called the OFDM that PN fills (PN Padding OFDM, PNP-OFDM).It is good that the PN sequence has an autocorrelation performance as training sequence, and time domain is a two-value, and time domain is handled characteristics such as simple.General PN sequence is refered in particular to the m sequence, and the m sequence length is 2 ^M-1, wherein M is a positive integer, inconvenience during with the auxiliary computation cycles convolution of FFT/IFFT when channel estimating, and the protection gap length selects seldom, therefore needs to consider the expansion of m sequence or block.The expansion of m sequence or block and can regard broad sense PN sequence as is the continuation of m sequence just as PN420 in the China Digital TV ground transmission standard and PN945, and its frame structure as shown in Figure 4.And PN595 is blocking of m sequence, and they can regard broad sense PN sequence as.Referring to document [digital television ground broadcast transmission system frame structure, chnnel coding and modulation, State Standard of the People's Republic of China GB20600-2006].Because broad sense PN sequence generally is not smooth at frequency domain, so sequence can be amplified noise when using FFT to carry out channel estimating.Broad sense PN sequence with used length L=420 of filling in the Chinese ground digital standard is an example, in low 0.08 of the standard deviation that reaches of minimum radius of DFT transform domain.Behind the division arithmetic through the DFT territory, the noise that minimum radius DFT is ordered is exaggerated 1/0.08 times.Through calculating, noise power on average has been exaggerated 4.09 times, and promptly noise has been exaggerated 6.11dB.

Chinese invention patent [based on the frequency domain channel estimation method that two-value full-pass sequence protection interval is filled, application number 200710065404.9] has proposed a kind of two-value full-pass sequence (BinaryAll Pass, fill method BAP) of utilizing.Characteristics such as the BAP sequence has the frequency domain constant amplitude, and autocorrelation performance is good, and carry out frequency domain channel when estimating computational complexity low, the estimated accuracy height.The shortcoming of BAP sequence is that the peak-to-average force ratio value is higher, the time domain more complicated of being correlated with.

Summary of the invention

At problems of the prior art, to the modulating system of filling based on training sequence, in order to reduce the relevant complexity of time domain, channel estimating complexity and to improve time domain closing precision, precision of channel estimation mutually, the present invention proposes a kind of broad sense Legendre sequence or its inverse discrete Fourier transformer inverse-discrete utilized as the fill method of training sequence and the communication system that adopts this method.

The broad sense Legendre sequence of definition comprises Legendre symbol, Legendre sequence, expansion Legendre sequence.Legendre symbol is based on the quadratic residue structure, and its length L is a prime number, and its building method is:

Legendre symbol c=[c (0), c (1), c (L-1)] frequency domain C satisfy:

$C\left(i\right)=\sqrt{L}c\left(i\right),$ 0≤i＜L，L≡1(mod4)

$C\left(i\right)=-j\sqrt{L}c\left(i\right),$ 0≤i＜L，L≡3(mod4)

The frequency domain, the time domain that are Legendre symbol satisfy linear relationship.And Legendre symbol has odd symmetry during L ≡ 3 (mod4), and Legendre symbol has even symmetry during L ≡ 1 (mod4).Referring to document [M.R.Schroeder, Number Theory in Scienceand Communication:With Applications in Cryptography, Physics, Digital Information, Computing, and Self-Similarity, Fourth Edition, Springer, 2006, pp.181-189].

Legendre sequence is a binary sequence with optimal period auto-correlation function based on the Hadamard difference set, and its length L is a prime number, and satisfies surplus the mould 43, and its building method is similar to Legendre symbol:

Referring to document [H.J.Zepernick, A.Finger, Pseudo Random Signal Processing:Theory andApplication, John Wiley﹠amp; Son, 2005, pp.106-112].

Legendre sequence c=[c (0), c (1), c (L-1)] frequency domain C satisfy:

$C\left(i\right)=\left\{\begin{array}{cc}1,& i=0\\ 1-j\sqrt{L}c(i,)& 0<i<L\end{array}\right.$

The expansion Legendre sequence is a kind of Legendre sequence that the present invention defines, and its length L is a prime number, and satisfies surplus the mould 41, and its building method is:

J wherein ²=-1.Expansion Legendre sequence c=[c (0), c (1), c (L-1)] frequency domain C satisfy:

$C\left(i\right)=\left\{\begin{array}{cc}j,& i=0\\ \sqrt{L}c\left(i\right)+j,& 0<i<L\end{array}\right.$

In addition, the tectonic sequence that obtains after the negate of aforementioned expansion Legendre sequence, upset, the cyclic shift also can reduce the expansion Legendre sequence.

The broad sense Legendre sequence is more than m sequence selectable lengths; usually can find the broad sense Legendre sequence of more approaching protection gap length; thereby avoid adopting the frame structure of Fig. 4 form, this frame structure may make synchronizing process capture wrong peak position and preceding path position under multipath channel.Length be 192 broad sense PN sequence slip correlated results as shown in Figure 5, length be 191 Legendre sequence slip correlated results as shown in Figure 6.Among Fig. 5, under the white Gaussian noise channel, 3 peak values have appearred in broad sense PN sequence; And in Fig. 6, the broad sense Legendre sequence has only a peak value.More interference peak value occurred owing to adopt broad sense PN sequence to compare, made when adopting broad sense PN sequence, captured wrong preceding path position easily with the broad sense Legendre sequence; Therefore under the multipath situation, wrong situation more may appear catching in broad sense PN sequence.In addition, because Legendre sequence has odd symmetry or even symmetry, therefore can utilize correlator configuration to simplify the related operation complexity.For example, can adopt a kind of correlator configuration as shown in Figure 7 to simplify the related operation complexity.

Broad sense Legendre sequence time domain two-value or three values, and time domain, frequency domain are smooth.Length be 192 broad sense PN sequence time domain, frequency domain amplitude characteristic as shown in Figure 8, length be 191 Legendre sequence time domain, frequency domain amplitude characteristic as shown in Figure 9.As seen from Figure 8, broad sense PN sequence frequency domain unevenness is carried out channel estimating meeting fault in enlargement; As seen from Figure 9, Legendre's sequence frequency domain is smooth, carries out the precision of channel estimation height.The inverse discrete Fourier transformer inverse-discrete of using the broad sense Legendre sequence in addition is as training sequence, and its frequency domain two-value, frequency domain channel estimate that complexity is low.

To sum up, the present invention proposes protection fill method and communication system thereof at interval in a kind of orthogonal FDM modulation system.

Wherein, protection fill method at interval specifically comprises in described a kind of orthogonal FDM modulation system:

Protection fill method at interval in a kind of orthogonal FDM modulation system between the transmission data of system, utilizes broad sense Legendre sequence or its inverse discrete Fourier transformer inverse-discrete to fill protection at interval as training sequence, and its step is as follows:

Steps A: according to given protection gap length, search is near the broad sense Legendre sequence of this length;

Step B: select broad sense Legendre sequence or its inverse discrete Fourier transformer inverse-discrete as training sequence;

Step C:, select the infilled frame structure of training sequence according to selected training sequence length;

Step D: making a start obtains base band output successively with training sequence and transmission data after framing and back-end processing;

Step e: receiving end receives and transmits, and obtains timing, carrier deviation information by transmitting of receiving end reception made the relevant relevant peaks that obtains with training sequence, and proofreaies and correct timing, carrier deviation;

Step F: receiving end separated transmission data and training sequence, and reconstruct training sequence and channel estimating circular convolution;

Step G: the discrete Fourier transform (DFT) of calculation training sequence and channel estimating circular convolution, finish channel estimating.

Further, described broad sense Legendre sequence is:

Legendre symbol;

Perhaps,

Legendre sequence;

Perhaps,

The expansion Legendre sequence, the length of described expansion Legendre sequence is L, and L is a prime number, and surplus the L mould 41, its building method is:

First symbol is j, and all the other symbols utilize quadratic residue method construct, wherein j ²=-1.

Further, described expansion Legendre sequence also comprises:

The tectonic sequence that obtains after the tectonic sequence negate that described building method is obtained; Perhaps,

The tectonic sequence that obtains after the tectonic sequence upset that described building method is obtained; Perhaps,

The tectonic sequence that obtains after the tectonic sequence cyclic shift that described building method is obtained.

Further, time domain, the frequency domain of described Legendre symbol all be 0 ,-1, three value sequences of+1}, time domain, frequency domain are identical;

Perhaps,

The time domain of described Legendre sequence is that { 1, the binary sequence of+1}, frequency domain are three value sequences;

Perhaps,

The time domain of described expansion Legendre sequence is that { 1 ,+1, three value sequences of j}, frequency domain are three value sequences;

Perhaps,

The inverse discrete Fourier transformer inverse-discrete frequency domain of Legendre sequence be 1, the binary sequence of+1}, time domain is three value sequences;

Perhaps,

The expansion Legendre sequence the inverse discrete Fourier transformer inverse-discrete frequency domain be 1 ,+1, three value sequences of j}, time domain is three value sequences.

Further, described step C comprises:

If protection gap length N then adopts the frame structure of training sequence continuation greater than the training sequence length L;

If protection gap length N less than the training sequence length L, then adopts training sequence and the overlapping frame structure of transmission data;

If protection gap length N equals the training sequence length L, then directly adopt training sequence to fill protection at interval.

The communication system of the above-mentioned protection of described employing fill method at interval is specific as follows:

The communication system of filling at interval as protection based on training sequence in a kind of orthogonal FDM modulation system; between the transmission data of system; utilize broad sense Legendre sequence or its inverse discrete Fourier transformer inverse-discrete to fill protection at interval, also comprise in the described communication system with lower unit as training sequence:

Search unit: according to given protection gap length, near the broad sense Legendre sequence of this length, the broad sense Legendre sequence that search is obtained passes to selected cell in search;

Selected cell: select broad sense Legendre sequence or its inverse discrete Fourier transformer inverse-discrete as training sequence, the training sequence after selecting is passed to the frame structure filler cells;

Frame structure filler cells: according to selected training sequence length, select the infilled frame structure of training sequence, selected infilled frame structure is passed to make a start;

Make a start: making a start obtains base band output successively with training sequence and transmission data after framing and back-end processing;

Receiving end: receiving end receives and transmits, and obtains timing, carrier deviation information by transmitting of receiving end reception made the relevant relevant peaks that obtains with training sequence, and proofreaies and correct timing, carrier deviation; Receiving end separated transmission data and training sequence, and reconstruct training sequence and channel estimating circular convolution, and pass to channel estimating unit;

Channel estimating unit: the discrete Fourier transform (DFT) of channel estimating unit calculation training sequence and channel estimating circular convolution, finish channel estimating.

The employing broad sense Legendre sequence that the present invention proposes or its inverse discrete Fourier transformer inverse-discrete be as the communication means and the communication system thereof of training sequence, has training length and select manyly, and time domain is relevant simple, and frequency domain channel is estimated characteristics such as complexity is low, precision height.Use broad sense Legendre sequence or its inverse Fourier transform as the advantage of training sequence to be, broad sense Legendre sequence length is selected more, can more complete filling protect at interval; Frequency domain is smooth; Time domain two-value or three values, and have symmetry, time domain is handled easily; Frequency domain two-value or three values, the channel estimating computational complexity is low, the estimated accuracy height.

Description of drawings

Fig. 1 is a kind of structural representation of CP-OFDM frame format in the existing multicarrier system;

Fig. 2 is a kind of structural representation of ZP-OFDM frame format in the existing multicarrier system;

Fig. 3 is a kind of structural representation of PNP-OFDM frame format in the existing multicarrier system;

Fig. 4 is PN420, the PN945 frame structure schematic diagram that defines in the China Digital TV ground transmission standard;

Fig. 5 is that length is 192 broad sense PN sequence slip correlated results;

Fig. 6 is that length is 191 Legendre sequence slip correlated results;

Fig. 7 is the structural representation of Legendre sequence correlator;

Fig. 8 is that length is time domain, the frequency domain amplitude characteristic of 192 broad sense PN sequence;

Fig. 9 is that length is time domain, the frequency domain amplitude characteristic of 191 Legendre sequence;

Figure 10 is the method flow diagram that Legendre sequence and inverse discrete Fourier transformer inverse-discrete thereof are filled as training sequence;

Figure 11 is based on the frame structure schematic diagram of sequence continuation;

Figure 12 is based on the overlapping frame structure schematic diagram of sequence;

Figure 13 is based on the multicarrier modulation system transmitting terminal structured flowchart that training sequence is filled;

Figure 14 is the channel estimation results of the broad sense PN192 sequence of length 192;

Figure 15 is the channel estimation results of contrary discrete Fourier transform sequence of the expansion Legendre training sequence of length 193.

Embodiment

For making purpose of the present invention, content and advantage clearer, embodiment of the present invention is described further in detail below in conjunction with accompanying drawing.

Use Legendre sequence that the invention process provides and inverse discrete Fourier transformer inverse-discrete thereof have length and select various characteristic as the communication system of training sequence, can better meet the demand of the length of training sequence near whole protecting interval length; The time domain value set of broad sense Legendre sequence is little and have symmetry, can simplify relevant complexity; The smooth precision of channel estimation that improves of the frequency domain of broad sense Legendre sequence; The frequency domain of the inverse discrete Fourier transformer inverse-discrete sequence of broad sense Legendre sequence has binary feature, simplifies the channel estimating complexity.

Referring to Figure 10, shown the method flow that use Legendre sequence that the invention process provides and inverse discrete Fourier transformer inverse-discrete thereof are filled as training sequence, specifically may further comprise the steps:

Step 101: according to given protection gap length, search is near the broad sense Legendre sequence of this length;

Suppose modulating system protection gap length N=192, frame length M=1536.Search obtains near 192 prime number, and 191 and 193 are prime number, and 191 ≡ 3 (mod4), and 193 ≡ 1 (mod4) therefore have the Legendre sequence of length 191 and the expansion Legendre sequence of length 193.

Step 102: select broad sense Legendre sequence or its inverse discrete Fourier transformer inverse-discrete as training sequence;

Selectable lengths is that the inverse discrete Fourier transformer inverse-discrete of expansion Legendre sequence of 191 Legendre sequence or length 193 is as training sequence.

Step 103:, select the infilled frame structure of training sequence according to selected length;

Length be the length of 191 Legendre sequence less than the protection gap length, therefore select the frame structure of continuation, as shown in figure 11;

Length be the inverse discrete Fourier transformer inverse-discrete length of 193 expansion Legendre sequence greater than the protection gap length, but its first symbol amplitude only is other symbol power

Be other symbol energies than the big 22dB of first symbol, therefore can select overlapping frame structure, last symbol of first symbol and previous frame frame is overlaped, as shown in figure 12;

Step 104: making a start obtains base band output successively with training sequence and transmission data block after framing and back-end processing;

Input signal inserts training sequence between the frame then according to the method described above through chnnel coding, mapping, adaptive, the multicarrier/single-carrier modulated of framing, launches by radio-frequency front-end.As shown in figure 13.

Step 105: receiving end receives and to transmit, by received signal and transmitting training sequence being done relevantly obtain that relevant peaks obtains regularly, carrier deviation information, and correction timing, carrier deviation;

By slip relevant the obtain relevant peaks of local broad sense Legendre sequence, utilize the characteristic of relevant peaks to obtain regularly and the information of carrier deviation with received signal.But list of references [Z.X Yang, J.Wang, C.Y.Pan, et al.A combined codeacquisition and symbol timing recovery method for TDS-OFDM, IEEE Trans.Broadcast., vol 49, no 3, pp.304-308, Sept.2003].

Step 106: receiving end mask data and training sequence, and reconstruct training sequence and channel estimating circular convolution;

Based on the channel estimation method that training sequence is filled, there is training sequence and the data problem of mutual interference mutually, separate training sequence and data by the method for iteration.But list of references [J.Wang, Z.Yang, C.Y.Pan, et al.Iterative PaddingSubtraction of the PN Sequence for the TDS-OFDM over Broadcast Channels, IEEE Trans.Consumer Electronics, vol.51, no.4, pp.1148-1152, Nov.2005].The training sequence c (n) that can obtain length and be L is the linear convolution of the channel impulse response h (n) of L with length:

r(n)＝c(n)*h(n)+v(n)，0≤n＜2L

Wherein " * " represents linear convolution.Reconstruct obtains the circular convolution of training sequence and channel impulse response:

$y\left(n\right)=c\left(n\right)\&CircleTimes;h\left(n\right)+w\left(n\right),$ 0≤n＜L

Wherein

The expression circular convolution, w (n) v (n) is a circular convolution noise superimposed as a result, y (n) is obtained by following formula reconstruct:

y(n)＝r(n)+r(n+L)

Step 107: the discrete Fourier transform (DFT) of calculation training sequence and channel estimating circular convolution, finish channel estimating;

The discrete Fourier transform (DFT) of training sequence c (n) and training sequence and channel estimating circular convolution y (n) is respectively C (k), Y (k), if 0≤k＜L training sequence is the inverse discrete Fourier transformer inverse-discrete of Legendre sequence then C (k) is {+1, the binary sequence of-1}, then being estimated as of channel impulse response:

$\hat{h}\left(n\right)=\mathrm{IDFT}\left(\frac{Y\left(k\right)}{C\left(k\right)}\right)$

Since X (k) be+1, the binary sequence of-1}, the division arithmetic of channel estimating is very simple.Frequency domain owing to Legendre sequence is smooth in addition, the channel estimated accuracy height.But list of references [Y.Zeng; T.S.Ng, Pilot cyclic prefixed single carriercommunication:channel estimation and equalization, IEEE Signal Processing Letters, Vol 12, Issue1, Jan.2005, pp.56-59].Suppose channel h (n)=0.5 δ (n-10)+0.5 δ (n-30), signal to noise ratio snr=10dB, and ignore the interference of data to training sequence.The channel estimation results of the broad sense PN192 sequence of use length 192 as shown in figure 14, use length 193 expansion Legendre training sequence contrary discrete Fourier transform sequence channel estimation results as shown in figure 15, the channel estimation results of the contrary discrete Fourier transform sequence of the expansion Legendre training sequence of length 193 is accurate than broad sense PN192 sequence as can be seen.Further, the length that present embodiment provides is that the channel estimating of 193 expansion Legendre sequence also is similarly for Legendre sequence, Legendre symbol, and is similar in its step and the present embodiment, repeats no more here.

Above specific embodiments of the invention are had been described in detail, but the present invention is not restricted to the foregoing description.For example, also can take length among the present invention is 419,593,943 to wait the broad sense Legendre sequence of other length; And, use the sequence that the broad sense Legendre sequence is obtained by methods such as negate, upset, cyclic shifts.Within the spirit and principle of claim of the present invention, any modification of being done, be equal to and replace and improvement etc., all should be included within protection scope of the present invention.

Claims (10)

1. protect fill method at interval in an orthogonal FDM modulation system, it is characterized in that, between the transmission data of system, utilize broad sense Legendre sequence or its inverse discrete Fourier transformer inverse-discrete to fill protection at interval, comprise that step is as follows as training sequence:

Steps A: according to given protection gap length, search is near the broad sense Legendre sequence of this length;

Step B: select broad sense Legendre sequence or its inverse discrete Fourier transformer inverse-discrete as training sequence;

Step C:, select the infilled frame structure of training sequence according to selected training sequence length;

Step D: making a start obtains base band output successively with training sequence and transmission data after framing and back-end processing;

Step e: receiving end receives and transmits, and obtains timing, carrier deviation information by transmitting of receiving end reception made the relevant relevant peaks that obtains with training sequence, and proofreaies and correct timing, carrier deviation;

Step F: receiving end separated transmission data and training sequence, and reconstruct training sequence and channel estimating circular convolution;

Step G: the discrete Fourier transform (DFT) of calculation training sequence and channel estimating circular convolution, finish channel estimating.

2. method according to claim 1 is characterized in that, described broad sense Legendre sequence is:

Legendre symbol;

Perhaps,

Legendre sequence;

Perhaps,

The expansion Legendre sequence, the length of described expansion Legendre sequence is L, and L is a prime number, and surplus the L mould 41, its building method is:

First symbol is j, and all the other symbols utilize quadratic residue method construct, wherein j ²=-1.

3. method according to claim 2 is characterized in that, described expansion Legendre sequence also comprises:

The tectonic sequence that obtains after the tectonic sequence negate that described building method is obtained; Perhaps,

The tectonic sequence that obtains after the tectonic sequence upset that described building method is obtained; Perhaps,

The tectonic sequence that obtains after the tectonic sequence cyclic shift that described building method is obtained.

4. method according to claim 2 is characterized in that,

Time domain, the frequency domain of described Legendre symbol all be 0 ,-1, three value sequences of+1}, time domain, frequency domain are identical;

Perhaps,

The time domain of described Legendre sequence is that { 1, the binary sequence of+1}, frequency domain are three value sequences;

Perhaps,

The time domain of described expansion Legendre sequence is that { 1 ,+1, three value sequences of j}, frequency domain are three value sequences;

Perhaps,

The inverse discrete Fourier transformer inverse-discrete frequency domain of Legendre sequence be 1, the binary sequence of+1}, time domain is three value sequences;

Perhaps,

The expansion Legendre sequence the inverse discrete Fourier transformer inverse-discrete frequency domain be 1 ,+1, three value sequences of j}, time domain is three value sequences.

5. according to claim 1 or 2 or 3 or 4 described methods, it is characterized in that described step C further comprises:

If protection gap length N then adopts the frame structure of training sequence continuation greater than the training sequence length L;

If protection gap length N less than the training sequence length L, then adopts training sequence and the overlapping frame structure of transmission data;

If protection gap length N equals the training sequence length L, then directly adopt training sequence to fill protection at interval.

6. the communication system of filling at interval as protection based on training sequence in the orthogonal FDM modulation system; it is characterized in that; between the transmission data of system; utilize broad sense Legendre sequence or its inverse discrete Fourier transformer inverse-discrete to fill protection at interval, also comprise in the described communication system with lower unit as training sequence:

Search unit: according to given protection gap length, near the broad sense Legendre sequence of this length, the broad sense Legendre sequence that search is obtained passes to selected cell in search;

Selected cell: select broad sense Legendre sequence or its inverse discrete Fourier transformer inverse-discrete as training sequence, the training sequence after selecting is passed to the frame structure filler cells;

Frame structure filler cells: according to selected training sequence length, select the infilled frame structure of training sequence, selected infilled frame structure is passed to make a start;

Make a start: making a start obtains base band output successively with training sequence and transmission data after framing and back-end processing;

Receiving end: receiving end receives and transmits, and obtains timing, carrier deviation information by transmitting of receiving end reception made the relevant relevant peaks that obtains with training sequence, and proofreaies and correct timing, carrier deviation; Receiving end separated transmission data and training sequence, and reconstruct training sequence and channel estimating circular convolution, and pass to channel estimating unit;

Channel estimating unit: the discrete Fourier transform (DFT) of channel estimating unit calculation training sequence and channel estimating circular convolution, finish channel estimating.

7. communication system according to claim 6 is characterized in that, described broad sense Legendre sequence is:

Legendre symbol;

Perhaps,

Legendre sequence;

Perhaps,

The expansion Legendre sequence, the length of described expansion Legendre sequence is L, and L is a prime number, and surplus the L mould 41, its building method is:

First symbol is j, and all the other symbols utilize quadratic residue method construct, wherein j ²=-1.

8. communication system according to claim 7 is characterized in that, described broad sense Legendre sequence is:

The tectonic sequence that obtains after the tectonic sequence negate that described building method is obtained; Perhaps,

The tectonic sequence that obtains after the tectonic sequence upset that described building method is obtained; Perhaps,

The tectonic sequence that obtains after the tectonic sequence cyclic shift that described building method is obtained.

9. communication system according to claim 6 is characterized in that,

Time domain, the frequency domain of described Legendre symbol all be 0 ,-1, three value sequences of+1}, time domain, frequency domain are identical;

Perhaps,

The time domain of described Legendre sequence is that { 1, the binary sequence of+1}, frequency domain are three value sequences;

Perhaps,

The time domain of described expansion Legendre sequence is that { 1 ,+1, three value sequences of j}, frequency domain are three value sequences;

Perhaps,

The inverse discrete Fourier transformer inverse-discrete frequency domain of Legendre sequence be 1, the binary sequence of+1}, time domain is three value sequences;

Perhaps,

The expansion Legendre sequence the inverse discrete Fourier transformer inverse-discrete frequency domain be 1 ,+1, three value sequences of j}, time domain is three value sequences.

10. according to claim 6 or 7 or 8 or 9 described communication systems, it is characterized in that described frame structure filler cells is selected frame structure in the following manner:

If protection gap length N then adopts the frame structure of training sequence continuation greater than the training sequence length L;

If protection gap length N less than the training sequence length L, then adopts training sequence and the overlapping frame structure of transmission data;

If protection gap length N equals the training sequence length L, then directly adopt training sequence to fill protection at interval.

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