CN1812387A - Orthogonal frequency division multiplexing communication method using prefix and suffix signals - Google Patents

Abstract

This invention discloses a kind of prefix and postfix signals used orthogonal frequency division multiplex transmission method. The prefix and postfix signals are acquired in this way: some modulated data symbols are positioned in the OFDM frequency domain frame block. The pilot symbols that the receiving end knows are positioned in other spaces. The constant-spacing evenly extracting is carried out to OFDM frequency domain frame block. Thus, a new frequency domain frame block is got. The data symbols in the new frequency domain frame block are set to zero, pilot symbols are kept constant. Then, the amplitude of new frequency domain frame block is contracted, then carries out IDFT and multiplies by frequency shift signal corresponded to extracting initiated position.

Description

Used the orthogonal frequency division multiplexing communication method of preceding suffix signal

Technical field

The present invention relates to a kind of orthogonal frequency division multiplexing communication method, relate in particular to a kind of orthogonal frequency division multiplexing communication method that uses preceding suffix signal.

Background technology

Wireless communication technology is maked rapid progress, and develops very rapid.People also have higher requirement to wireless communication technology: better mobility, more reliable, higher transmission rate.People not only have been satisfied with wireless transmission of voice, also requirement can wirelessly transmitting data with visit internet, wireless transmitted image, even video.

Wireless transmission channel is more complicated and badly many than other communications media.The situation of channel itself, and communication control processor becomes the most significant problems that wireless communication technology faces to the estimation of channel conditions.The multidiameter delay of channel is expanded to the traffic symbols of two-forty emission and is brought intersymbol interference, shows as frequency selective fading at frequency domain, and this is the major obstacle that wireless communication system need overcome.Before OFDM (OFDM) technology occurred, people had only the transmission characteristic that adopts time-domain adaptive equalizer to improve channel, but when the multidiameter delay expansion of channel is very big, to such an extent as to the too high computation complexity of required equalizer exponent number is difficult to acceptance.

The appearance of OFDM technology has solved aforesaid difficulty well.The symbols streams that tradition OFDM technology will send at a high speed is decomposed into the multi-path low speed symbols streams, be modulated at respectively on the mutually orthogonal different sub carrier of parallel transmission, equivalence is used for frequency-selective channel being decomposed into a large amount of parallel non-frequency selectivity subchannels, promptly concerning each subchannel, all be equivalent to not have time delay expansion (the channel delay expansion can be ignored with respect to the low speed symbol), have only phase shift and changes in amplitude (but phase shift and changes in amplitude that each subchannel produces signal have nothing in common with each other) during signal process subchannel, at this moment will become quite simple to signal processing in each subchannel, need not equilibrium, only need to correct once taking advantage of again of phase shift and amplitude.Tradition OFDM technology is introduced protection (guard interval) at interval between the time domain OFDM symbol, and inserts Cyclic Prefix (CP--cyclic prefix) therein.CP is the straightforward procedure that keeps sub-carrier orthogonality when having the multidiameter delay expansion in the channel, this makes that carrying out simple frequency domain in receiving end handles (correcting phase shift and answering of amplitude takes advantage of) just energy restore data, and need not complicated time-domain adaptive equalizer, Here it is so-called CP-OFDM.CP is the simple copy of part signal in the OFDM symbol body, is the mixed signal of one section incomplete pilot sub-carrier and data subcarrier, need take transmitting power.Because CP directly copies the part from OFDM symbol body, is actually a part of redundant information, so the CP-OFDM receiver can utilize CP to finish catching with synchronously, to carry out subsequent treatment signal.As shown in Figure 1, be CP-OFDM time-domain symbol sequence schematic diagram.Here, " the OFDM symbol " mentioned among the present invention, " OFDM symbol body ", " OFDM time-domain symbol " all refer to " OFDM symbol:x " part among the figure, and wherein x is a numeral, represents the sequence number of this symbol.

But adopt the disadvantage of the CP-OFDM of frequency domain processing to be: when occurring " response is zero " on some subchannel (the signal attenuation great situation of this subchannel to wherein transmitting), the whole error performance of system can seriously descend.And the appearance of ZP-OFDM (ZP-zero padding) has well overcome this problem.ZP-OFDM does not launch any signal in protection at interval, so receiving end can obtain time domain and do not have the OFDM symbol of crosstalking, and then can handle (block equilibrium) by the special time domain of receiving terminal and avoid " frequency response zero point " acquisition than CP-OFDM more performance.But because ZP-OFDM no signal emission in protection at interval; therefore in order receiver to be easy to finish, send the reduction that this section sequence can cause system transmissions efficient needed extra time to the catching and need the extra one section known synchronizing sequence that sends synchronously of signal.As shown in Figure 2, be ZP-OFDM time-domain symbol sequence schematic diagram.

CP-OFDM is difficult to adopt the time domain processing method of similar ZP-OFDM, this is because from time domain, when having the multidiameter delay expansion in the channel, the hangover of CP and OFDM symbol are superimposed, the CP of the hangover of OFDM symbol and next OFDM symbol is superimposed, the data subcarriers that also have simultaneously a lot of the unknowns among the CP except the known pilot sub-carrier of small part, thereby be difficult in time domain and CP cut crosstalking of OFDM symbol and obtain time domain and do not have the OFDM symbol of crosstalking, and then also be difficult to use the time domain block balancing technique among the ZP-OFDM to improve frequency domain " zero point " performance.

Also have known training sequence (for example m sequence, M sequence, PN sequences such as Barker code) is inserted into way in the protection at interval; owing to be to be inserted in the protection at interval, therefore can not cause the extra increase in transmission time, and can finish and catch; synchronously, function such as channel estimating.But there are not any inner link in these sequences and OFDM symbol, and when the multidiameter delay expansion of channel was very serious, these sequences caused interference to the OFDM symbol, have destroyed the orthogonality between the OFDM symbol subcarrier simultaneously.Want the interference of training sequence to the OFDM symbol cut, prerequisite is channel to be had as far as possible accurately estimate, and the destruction of phase mutual interference between training sequence and the OFDM symbol and sub-carrier orthogonality makes channel estimating performance be restricted, and then the whole system performance is restricted.As shown in Figure 3, be the time-domain symbol sequence schematic diagram of this way.

Summary of the invention

At the existing problem and shortage of above-mentioned existing orthogonal frequency division multiplexing communication method, the purpose of this invention is to provide a kind of channel estimating performance and receiver of can improving greatly and be easy to the signal orthogonal frequency division multiplexing communication method of preceding suffix signal that carried out synchronous use.

The present invention is achieved in that a kind of orthogonal frequency division multiplexing communication method that uses preceding suffix signal, and described preceding suffix signal obtains like this:

In OFDM frequency domain frame piece, place some modulated data symbols, all the other place the known frequency pilot sign of receiving terminal, OFDM frequency domain frame piece is uniformly-spaced evenly extracted, obtain a new frequency domain frame piece, with the data symbol zero setting in this new frequency domain frame piece, frequency pilot sign remains unchanged, and then this new frequency domain frame piece amplitude is carried out convergent-divergent and carries out reverse discrete fourier transform (IDFT) again and multiply by the frequency shift signal corresponding with extracting original position.

Preferably, the OFDM symbol of this method transmission has two kinds, promptly directly carries out OFDM symbol (can be described as naked OFDM symbol) that IDFT obtains and OFDM symbol by OFDM frequency domain frame piece and adds that being conjugated in the symbol that constitutes together before and after it (also cries and have the OFDM symbol that sew front and back: PP OFDM symbol).

Preferably, when described OFDM symbol is sewed the symbol transmission of composition before and after adding, OFDM frequency domain frame piece is carried out the IDFT conversion, makes it become the time domain OFDM symbol that can in channel, transmit, and before and after this OFDM symbol, add described before suffix signal.

Preferably, the described symbol that carries out from OFDM frequency domain frame piece is regarded all symbols in the OFDM frequency domain frame piece as end to end annular closed symbol sebolic addressing when extracting, symbolic number in the OFDM frequency domain frame piece can be extracted at interval and divide exactly, extract not necessarily first sign-on from OFDM frequency domain frame piece of original position, divide exactly but the total number of symbols before the original position can be extracted the interval.

Preferably, the described symbol that carries out from OFDM frequency domain frame piece is when extracting, and the frequency pilot sign of extraction is The more the better.

Preferably, the described zoom factor k that new frequency domain frame piece amplitude is carried out convergent-divergent calculates like this:

If contain M symbol in each OFDM frequency domain frame piece, the extraction space-number is G, contain X OFDM symbol altogether in a certain OFDM symbol time sequence, Y the OFDM symbol of sewing before and after having wherein arranged, all the other are naked OFDM symbol, and the power of each data subcarrier in the OFDM symbol of each the data symbol correspondence in the OFDM frequency domain frame piece is Power _D, the power of each pilot sub-carrier is Power _P, the pilot sub-carrier number that the OFDM symbol of sewing before and after Y has contains respectively is: P ₀, P ₁... P _Y-1, the pilot sub-carrier number that Y contains respectively during front and back are sewed is: Q ₀, Q ₁... Q _Y-1, generate the computing formula that y sews used zoom factor k to front and back and be:

$k=\sqrt{\frac{\underset{y=0}{\overset{Y-1}{\mathrm{\Σ}}}{P}_y+\frac{{\mathrm{Power}}_D}{{\mathrm{Power}}_P}[\mathrm{XM}-\underset{y=0}{\overset{Y-1}{\mathrm{\Σ}}}{P}_y]}{{\mathrm{XGQ}}_y}.}$

Preferably, the OFDM symbol of sewing before and after described having can be used for channel estimating double as carrying simultaneously data, and channel can reduce its emission frequency when stablizing, can strengthen its emission frequency when channel variation is very fast.

Preferably, described data symbol modulation system can be any in BPSK, QPSK, 16QAM, the 64QAM modulation system; The frequency pilot sign modulation system is the BPSK modulation.

Preferably, this method also comprises, the receiver end PP that is concerned with adds closing operation, this is operating as: with that segment signal and OFDM symbol initial and preceding suffix signal isometric that segment signal addition isometric with preceding suffix signal after the ending of OFDM symbol, the mixed signal that sew the OFDM symbol that the formation circulation is complete and the complete front and back of circulation of zero padding, this mixed signal is carried out discrete fourier transform (DFT), can make the frequency pilot sign in the former OFDM frequency domain frame piece be strengthened by equivalence, with obtain the pilot frequency locations place more precise channels estimate, thereby improve whole channel estimated accuracy; Utilize the result of this channel estimating, to sew through the front and back after the channel at receiving terminal and to deduct, obtain time domain and do not have the naked OFDM symbol of crosstalking, then this naked OFDM symbol is carried out block MMSE/ZF (block least mean-square error or ZF) equilibrium, finally obtain valuation, finish transmission of Information data symbol in the OFDM frequency domain frame piece.

Preferably, receiving terminal is at first caught OFDM symbol head before the PP that is concerned with adds closing operation, afterwards carrier wave frequency deviation is estimated and compensated, wherein, the autocorrelation performance of suffix signal before utilizing, can adopt and utilize the catching of Cyclic Prefix, Nonlinear Transformation in Frequency Offset Estimation and backoff algorithm to finish among the similar CP-OFDM, also front and back can be sewed and regard one section PN sequence as, can utilize in the cdma system ripe estimation and backoff algorithm to finish based on the catching of PN sequence, carrier wave frequency deviation.

The present invention is for filling communication system-PP-OFDM that sew novel front and back in the protection between the OFDM symbol at interval, wherein the implication of PP is pilot tone prefix/postfix (pilot prefix/postfix).The generating mode of PP is different from CP, ZP and other known training sequence, and its maximum characteristics are that PP and OFDM symbol itself exist inner link, gets in touch with the mode of simple copy unlike CP.CP is the front that is added in the OFDM symbol, and PP then is that the back, front all will add.Utilize these characteristics, PP is brought about a wholesome effect to the OFDM symbol through corresponding unique processing means in the receiver.(ideal synchronisation has referred to accurately capture the position of OFDM symbol head when experiment condition and hypothesis receiving terminal have obtained ideal synchronisation on an equal basis, and carrier wave frequency deviation is also accurately corrected), the channel estimating performance of PP-OFDM system is better than CP-OFDM and ZP-OFDM, error performance is better than CP-OFDM, near ZP-OFDM.But PP has the autocorrelation performance similar to CP, and for receiver is one section known signal, therefore can make receiver be easy to finish, can obtain the efficiency of transmission higher than ZP-OFDM to the catching and synchronously, compare ZP-OFDM and need not the sequence that the extra time is used to send synchronous usefulness of signal.

Description of drawings

Fig. 1 is existing CP-OFDM time-domain symbol sequence schematic diagram;

Fig. 2 is existing ZP-OFDM time-domain symbol sequence schematic diagram;

Fig. 3 is for inserting the OFDM time-domain symbol sequence schematic diagram of other known arrays in the existing protection at interval;

Fig. 4 is a PP generating mode schematic diagram of the present invention;

Fig. 5 is a PP-OFDM time-domain symbol sequence schematic diagram of the present invention;

Fig. 6 is the relevant PP adduction method operation chart of the present invention;

Fig. 7 is a PP-OFDM transmitter architecture schematic diagram of the present invention;

Fig. 8 is a PP-OFDM receiver structure schematic diagram of the present invention;

Fig. 9 is that PP-OFDM of the present invention and CP-OFDM, ZP-OFDM error performance contrast schematic diagram;

Figure 10 is PP-OFDM of the present invention and CP-OFDM, ZP-OFDM channel estimating MSE performance comparison schematic diagram;

Figure 11 postpones the output result schematic diagram of correlator for PP-OFDM of the present invention system receiving end;

Figure 12 is carrier wave frequency deviation valuation output result schematic diagram of the present invention.

Embodiment

As shown in Figure 7, as seen from the figure, transmitter of the present invention mainly is made of Base-Band Processing (part that the two-wire dark square impales), digital to analog converter, up-conversion and radio frequency unit three parts.Data b it stream becomes baseband OFDM symbol sampler point through Base-Band Processing, and these sampled points become analog signal through digital to analog converter, upconverts to predetermined frequency range at last and arrives aerial through radio-frequency (RF) power amplification and transmission antennas transmit.Solid line among the figure is a data flow, and dotted line is a control signal.The Base-Band Processing part can be finished by monolithic programmable logic chip (for example large-scale F PGA of altera corp or Xilinx company), DSP or ASIC.Flexible and convenient for what realize, Base-Band Processing partly contains a central controller, and it can be the Logic resource of a CPU or FPGA inside.At present at the inner CPU or very common that embeds of FPGA in the way of the inner embedding of DSP CPU, for example altera corp is embedded into (Excalibur family chip) among the FPGA with arm processor, Xilinx company is embedded into the PowerPC processor among the FPGA, and TI company is embedded into arm processor in the middle of the dsp chip.

Except central controller, Base-Band Processing comprises that mainly following functional part: RAM, two-port RAM, 2 select 1 switch, 3 to select 1 switch, withdrawal device, deserializer (S/P), parallel-to-serial converter (P/S), FFT arithmetic unit (finishing M point and A point IDFT), constellation mapping, digital FIR filter, multiplier.With upper-part collaborative work under the control of central controller, finish the Base-Band Processing function.

Data b it carries out rate-matched through two-port RAM, and then constellation mapping becomes data symbol.Circulate under the control of central controller output pilot tone bit and constellation mapping of the RAM that stores pilot tone bit becomes frequency pilot sign.Either-or switch is formed frequency domain frame piece (output of S/P) with top two kinds of symbols under central controller controls.Frequency domain frame piece forms OFDM symbol and PP respectively through two data paths.Three elections switch is exported under the control of central controller and is formed the OFDM symbol sebolic addressing, finishes Base-Band Processing through the extraradial digital FIR filter of inhibition zone at last.

As shown in Figure 8, as seen from the figure, receiver of the present invention mainly is made of AFE (analog front end) (radio frequency, automatic gain control, down-conversion, frequency overlapped-resistable filter), analog to digital converter, Base-Band Processing (part that big two-wire dark square impales) three parts.Aerial carrier wave wireless signal becomes amplitude and all comparatively suitable base-band analog signal of bandwidth through AFE (analog front end), then becomes baseband OFDM symbol sampler point through analog to digital converter, and these sampled points are reduced to data b it through Base-Band Processing.Solid line among the figure is a data flow, and dotted line is a control signal.

Receiver Base-Band Processing part can adopt and the similar hardware of transmitter Base-Band Processing part, but chip-scale should be bigger.Except central controller, Base-Band Processing mainly comprises following functional part: common RAM, two-port RAM, delayer, complex conjugate parts, moving average parts, deserializer (S/P), FFT arithmetic unit (finishing M point DFT), constellation is separated mapping means, digital FIR filter (channel simulation filter, time domain block equalizer) parts, based on the channel estimator of pilot tone, impulse response is given birth to device, adder, multiplier.With upper-part collaborative work under the control of central controller, finish the Base-Band Processing function.

Analog to digital converter is input to the Base-Band Processing part with OFDM symbol sampler point, at first postpones relevant treatment under the control of central controller, utilizes the sampled point sequence of two-port RAM storage certain depth simultaneously.Differentiate the existence of relevant peaks when central controller after, from two-port RAM, find the correct original position of OFDM symbol PP head, and output, central controller utilizes relevant peaks to calculate the sequence that output is used to correct carrier wave frequency deviation simultaneously, and correcting frequency deviation is made in the output of two-port RAM.Next utilize the output of two-port RAM to carry out " the relevant closing operation that adds of PP ", and pilot channel estimation.Utilize the valuation of channel estimation results generation channel impulse response, and impulse response is inserted the channel simulation filter.The RAM that has stored the PP signal in advance exports the PP signal identical with transmitter under the control of central controller, process channel simulation filter becomes the PP signal behind the local process channel of estimating of receiving end, from the output of two-port RAM, this part signal is deducted, then carry out time domain Block equilibrium, the tap coefficient of time domain block equalizer is calculated by the channel impulse response valuation.The output of time domain Block equilibrium is separated mapping dateout bit through constellation.

Transmitter OFDM symbols transmitted of the present invention has two kinds.A kind of is PP OFDM symbol, and it comprises pilot tone, can be used for doing channel estimating except that the carrying data.A kind of naked OFDM symbol (also with the OFDM symbol of sewing before and after other) for sewing without any front and back, this symbol only carries data.These two kinds of symbols alternately transmit, and transmit the frequency of PP OFDM symbol and can decide the requirement of channel estimating according to channel conditions and system, or variable.

As shown in Figure 4, PP OFDM symbol of the present invention is to generate like this: between OFDM frequency domain frame piece is carried out simply waiting evenly every extracting (extraction position should as much as possible covering pilot frequency locations), obtain a length original PP frequency domain frame piece short than OFDM frequency domain frame piece, then will be extracted into the data symbol zero setting in the original PP frequency domain frame piece, frequency pilot sign remains unchanged, and then this frequency domain frame piece amplitude is carried out convergent-divergent and carries out the IDFT conversion again and multiply by the frequency shift signal corresponding with extracting original position promptly having generated the PP signal.

If total M symbol in the OFDM frequency domain frame piece, wherein P frequency pilot sign can be distributed on P the position in any way, and all the other positions are data symbol.OFDM frequency domain frame piece transforms to time domain through IDFT and constitutes OFDM time-domain symbol (the OFDM symbol:x among Fig. 1, Fig. 2, Fig. 3).If M symbol in the OFDM frequency domain frame piece is followed successively by s ₀, s ₁... s _m... s _M-1, wherein the frequency pilot sign note is s _M0, s _M1... s _Mp... s _MP-1, promptly the indexed set of frequency pilot sign is: psi_P={m ₀, m ₁... m _p... m _P-1.Total M/G symbol in the original PP frequency domain frame piece, G is that integer and M can be divided exactly by G, defines A=M/G, and A is integer also, this means that guard interval length is A.The original position that extracts from OFDM frequency domain frame piece is not necessarily from s ₀Beginning can be from s _b, 0≤b≤M-1 begins, and is integer but b will satisfy b/G, regards M symbol as end to end annular closed symbol sebolic addressing during extraction and operates.Suppose that certain extraction is extracted into Q frequency pilot sign, A-Q data symbol altogether.The indexed set note of the frequency pilot sign that is pumped in former OFDM frequency domain frame piece done: psi_Q={m ₀, m ₁... m _q... m _Q-1∈ psi_P, with the data symbol zero setting of extracting among the result, frequency pilot sign remains unchanged, and obtains PP frequency domain frame piece.Before PP frequency domain frame piece is carried out IDFT, in order to make system good peak-to-average force ratio (PAR) is arranged, multiply by zoom factor k earlier.Before providing the expression formula of k, define the other system parameters earlier.

As shown in Figure 5, as seen from the figure, PP-OFDM of the present invention system is identical on the transmission time expense with the CP-OFDM system.But have at least between two PP OFDM symbols one what not with naked OFDM symbol.Consider one section PP-OFDM symbol time sequence that contains X OFDM symbol altogether, Y PP OFDM symbol wherein arranged, all the other are naked OFDM symbol, and the power that might as well establish each data subcarrier in the OFDM symbol of each the data symbol correspondence in the OFDM frequency domain frame piece is Power _D, the power of each pilot sub-carrier is Power _P, the pilot sub-carrier number that Y PP OFDM symbol contains respectively is: P ₀, P ₁... P _Y-1, Y to the pilot sub-carrier number that contains respectively among the PP is: Q ₀, Q ₁... Q _Y-1, generate y and be the computing formula of the used zoom factor k of PP:

$k=\sqrt{\frac{\underset{y=0}{\overset{Y-1}{\mathrm{\Σ}}}{P}_y+\frac{{\mathrm{Power}}_D}{{\mathrm{Power}}_P}[\mathrm{XM}-\underset{y=0}{\overset{Y-1}{\mathrm{\Σ}}}{P}_y]}{{\mathrm{XGQ}}_y}}$

After multiplying each other with zoom factor k, PP frequency domain frame piece is IDFT transforms to time domain and become original PP time-domain data blocks.Because the arbitrariness of the original position that extracts needs to give original PP time-domain data blocks to multiply by the time-domain signal that frequency displacement function arranged corresponding with extracting original position.If the point sequence in the original PP time-domain data blocks is ${\mathrm{<figure-callout\; id="0"\; label="S"\; filenames="A20051001128000181.png,A20051001128000201.png"\; state="\{\{state\}\}">S</figure-callout>}}_0^{\stackrel{\&OverBar;}{\mathrm{PP}}},{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="A20051001128000201.png"\; state="\{\{state\}\}">S</figure-callout>}}_1^{\stackrel{\&OverBar;}{\mathrm{PP}}}...S_{A-1}^{\stackrel{\&OverBar;}{\mathrm{PP}}},$ Multiply by frequency shift signal point sequence afterwards is ${\stackrel{\&OverBar;}{S}}_A^{\mathrm{PP}}=\{{\mathrm{<figure-callout\; id="0"\; label="S"\; filenames="A20051001128000181.png,A20051001128000201.png"\; state="\{\{state\}\}">S</figure-callout>}}_0^{\mathrm{PP}},{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="A20051001128000201.png"\; state="\{\{state\}\}">S</figure-callout>}}_1^{\mathrm{PP}}...S_{A-1}^{\mathrm{PP}}\},$ Then have:

$S_a^{\mathrm{PP}}=S_a^{\stackrel{\&OverBar;}{\mathrm{PP}}}\exp \left(W_M^{-\mathrm{ab}}\right),a=\mathrm{0,1}...A-1,W_M=\exp \left(\frac{-2\mathrm{\&pi;j}}{M}\right)$

Here implied data block s ₀, s ₁... s _i... s _N-1Carrying out the DFT conversion is defined as:

$s_k=\frac{1}{\sqrt{N}}\underset{i=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{s}_i{W}_N^{\mathrm{ik}},k=\mathrm{0,1}...N-1$

To data block s ₀, s ₁... s _k... s _N-1Carrying out the IDFT conversion is defined as:

$s_i=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{s}_k{W}_N^{-\mathrm{ik}},i=\mathrm{0,1}...N-1$

As shown in Figure 6, be that example has illustrated at receiver end it is how to utilize PP to produce wholesome effect based on the channel estimating performance of pilot tone in to OFDM symbol body with two footpath channels.The operation of its core is called " relevant PP adduction ".As can be seen from FIG., we have obtained satisfying with the similar two parts of CP-OFDM the mixing of circulation integrality signal through this operation back.Wherein first is the result of OFDM symbol body and multipath channel impulse response circular convolution for the complete OFDM symbol of circulation.Second portion is the complete PP of the circulation of zero padding, for the zero padding as a result of PP and multipath channel impulse response circular convolution to and OFDM symbol body isometric, this is because the length of PP is short than OFDM symbol body, is the 1/G of OFDM symbol body length.Only keep pilot portion and obtain because transmitting terminal PP itself carries out uniformly-spaced even extraction by OFDM frequency domain frame piece, therefore the PP part can strengthen just to the pilot amplitude in the OFDM frequency domain frame piece after receiving terminal carries out the DFT processing to become frequency domain again again, and the effect of enhancing is equivalent to pilot power by original Power _PIncrease and be Power _P(1+k).We can obtain the precise channels estimation more of pilot frequency locations place to utilize the equivalent pilot signal that strengthens, thereby improve whole channel estimated accuracy.

Concrete operation method is: suppose from the starting point of the PP prefix of OFDM symbol (OFDM symbol:x) backward altogether the time domain receiving sequence of M+3A point formation be: R={r ₀, r ₁... r _m... r _M+3A-1, PP is relevant to be added closing operation and can be expressed as follows:

{r _A，r _A+1...r _2A-1}＝{r _A，r _A+1...r _2A-1}+{r _A+M，r _A+M+1...r _2A+M-1}

Add closing operation afterwards with the { r in the sequence _A, r _A+1... r _A+M-1Altogether M point taking-up, can obtain one and longly be the sequence { μ of M ₀, μ ₁... μ _m... μ _M-1, this sequence is carried out M point DFT conversion obtain the long frequency domain data sequence { v of M that is ₀, v ₁... v _m... v _M-1.That transmits on the subchannel of subscript position set psi_P correspondence in our the known frequency domain data sequence is known pilot symbols, and wherein the indexed set of those frequency pilot signs that strengthened by PP is psi_Q.The complex gain H of the pairing subchannel of pilot frequency locations set psi_P _M0, H _M1... H _Mp... H _MP-1Can obtain as follows:

if?m _p∈psi_Q

$\mathrm{the}{\mathrm{n\; H}}_{m_p}=\frac{v_{m_p}}{s_{m_{\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="A20051001128000201.png"\; state="\{\{state\}\}">p</figure-callout>}}}\sqrt{1+K}}$ $\mathrm{else}{H_m}_p=\frac{{v_m}_p}{{s_m}_p}$

Complex gain on whole M subchannels can be obtained by the complex gain interpolation on the pilot subchannel.Interpolation method has the MMSE interpolation, linear interpolation, high order interpolation, Gauss interpolation, low-pass filtering interpolation or the like.

Be the method that frequency domain channel is estimated (i.e. complex gain on all subchannels) that from certain PP OFDM symbol, obtains above.The frequency domain channel of several PP OFDM symbols estimated that interpolation obtains before and after the channel frequency domain response at those naked OFDM symbol places can be gone up by the time, and interpolation method has the MMSE interpolation, linear interpolation, high order interpolation, Gauss interpolation, low-pass filtering interpolation or the like.Promptly the interpolation on advanced line frequency territory direction after the channel estimating that obtains pilot tone point on the whole time-frequency two-dimensional subchannel grid chart is carried out the interpolation on the time domain direction again, thereby obtains the estimation of all subchannels on the whole time-frequency two-dimensional grid chart.

Utilize the result of channel estimating, can will deduct through the PP after the channel, then naked OFDM symbol is carried out block MMSE/ZF (block least mean-square error or ZF) equilibrium, finally obtain valuation, finish transmission of Information the data symbol at receiving terminal.

The frequency domain response (complex gain of each subchannel) of channel is transformed to time domain, obtain the time domain impulse response sequence of channel: h _L={ h ₀, h ₁... h _l... h _L.L is a maximum multipath delay spread, and hypothesis is no more than the length (just can take into account the maximum delay expansion in the applied environment during length of system design guard interval, thereby always setting up this hypothesis most of the time) of guard interval here.The big I of L directly is set to A-1, perhaps obtains in the following manner:

Because the total M point of channel frequency domain response is formed, therefore transform to time domain and do not add that the length of time domain impulse response also is the M point before any processing: ${\stackrel{\&OverBar;}{h}}_{M-1}^O=\{{\mathrm{<figure-callout\; id="0"\; label="h"\; filenames="A20051001128000181.png,A20051001128000201.png"\; state="\{\{state\}\}">h</figure-callout>}}_0,{\mathrm{<figure-callout\; id="1"\; label="h"\; filenames="A20051001128000201.png"\; state="\{\{state\}\}">h</figure-callout>}}_1...h_l...h_{M-1}\},$ Therefrom the preceding L+1 point of intercepting is as h _L, L is for satisfying $\underset{m=0}{\overset{L}{\mathrm{\&Sigma;}}}{\left|\right|h_m\left|\right|}^2/\underset{m=0}{\overset{M-1}{\mathrm{\&Sigma;}}}{\left|\right|h_m\left|\right|}^2>\mathrm{th}$ Minimum value, th is certain predetermined threshold value, for example 80%, 90%.

The PP signal is output as through after the channel: ${\stackrel{\&OverBar;}{R}}_{A+L}^{\mathrm{PP}}={\stackrel{\&OverBar;}{S}}_A^{\mathrm{PP}}\&CircleTimes;{\stackrel{\&OverBar;}{h}}_L=\{{\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="A20051001128000181.png,A20051001128000201.png"\; state="\{\{state\}\}">r</figure-callout>}}_0^{\mathrm{PP}},{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="A20051001128000201.png"\; state="\{\{state\}\}">r</figure-callout>}}_1^{\mathrm{PP}}...r_{A+L-1}^{\mathrm{PP}}\},$  represents the linear convolution operation.

From R with the R at OFDM symbol two ends _A+L ^PPDeduct and can be expressed as follows:

$\{{\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="A20051001128000181.png,A20051001128000201.png"\; state="\{\{state\}\}">r</figure-callout>}}_0,{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="A20051001128000201.png"\; state="\{\{state\}\}">r</figure-callout>}}_1...r_{A+L-1}\}=\{{\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="A20051001128000181.png,A20051001128000201.png"\; state="\{\{state\}\}">r</figure-callout>}}_0,{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="A20051001128000201.png"\; state="\{\{state\}\}">r</figure-callout>}}_1...r_{A+L-1}\}-\{{\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="A20051001128000181.png,A20051001128000201.png"\; state="\{\{state\}\}">r</figure-callout>}}_0^{\mathrm{PP}},{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="A20051001128000201.png"\; state="\{\{state\}\}">r</figure-callout>}}_1^{\mathrm{PP}}...r_{A+L-1}^{\mathrm{PP}}\}$

$\{r_{M+A},r_{M+A+1}...r_{M+2A+L-1}\}=\{r_{M+A},r_{M+A+1}...r_{M+2A+L-1}\}-\{{\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="A20051001128000181.png,A20051001128000201.png"\; state="\{\{state\}\}">r</figure-callout>}}_0^{\mathrm{PP}},{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="A20051001128000201.png"\; state="\{\{state\}\}">r</figure-callout>}}_1^{\mathrm{PP}}...r_{A+L-1}^{\mathrm{PP}}\}$

Then therefrom take out { r _A, r _A+1... r _2A+M-1As the input vector R of block MMSE equilibrium _A+M=[r _A, r _A+1... r _2A+M-1] ^T, subscript T represents transposition.If the balanced usefulness of block M * (A+M) matrix is D _{M * (A+M)}, then M * 1 column vector of balanced output can be expressed as: ${\stackrel{\&OverBar;}{R}}_M^E=D_{M\&times;(A+M)}{\stackrel{\&OverBar;}{R}}_{A+M},$ R _M ^EIn subscript do not belong to those elements of gather psi_P and both be the valuation of data symbol transmission.Balanced matrix can be tried to achieve as follows:

MMSE： $D_{M\&times;(A+M)}^{\mathrm{MMSE}}=F_M{H}_{(A+M)\&times;M}^H{({\mathrm{\&sigma;}}_n^{2}I+H_{(A+M)\&times;M}\&times;H_{(A+M)\&times;M}^H)}^{-1}$

ZF： $D_{M\&times;(A+M)}^{\mathrm{ZF}}=F_M{H}_{(A+M)\&times;M}^{+}$

F _MBe the DFT transformation matrix of M * M, element wherein is defined as according to DFT:

$f_{\mathrm{ij}}=\frac{1}{\sqrt{\mathrm{<figure-callout\; id="1"\; label="M\; W"\; filenames="A20051001128000201.png"\; state="\{\{state\}\}">M</figure-callout>}}}{W}_{}^{}{}_{1\mathrm{Mj}}^{\mathrm{ij}}$ Represent the ranks subscript of matrix element respectively.

Subscript H represents conjugate transpose.Subscript+represent pseudoinverse.σ _n ²For symbol power is normalized to 1 o'clock noise power, be equivalent to " jamtosignal ".Original noise power can be by h _M-1 ^OMiddle subscript obtains greater than those some statistics of L.Specifically ask method as follows:

For the OFDM symbol that contains pilot tone:

${\mathrm{\&sigma;}}_n^2=\frac{1}{({\mathrm{Power}}_D(M-P)+{\mathrm{Power}}_{P}P)/M}\&times;\frac{\underset{l=L+1}{\overset{M-1}{\mathrm{\&Sigma;}}}{\left|\right|h_l\left|\right|}^2}{M-L-1}$

For the OFDM symbol that does not contain pilot tone:

${\mathrm{\&sigma;}}_n^2=\frac{1}{{\mathrm{Power}}_D}\&times;\frac{\underset{l=L+1}{\overset{M-1}{\mathrm{\&Sigma;}}}{\left|\right|h_l\left|\right|}^2}{M-L-1}$

I represents unit matrix.H _{(A+M) * M}Be (A+M) * Metzler matrix, constitute as follows by the valuation of channel impulse response:

Receiving terminal at first needs to finish the operation of catching to OFDM symbol head before the PP that is concerned with adds closing operation, could determine the correct original position of aforementioned sequence of operations like this.Also to finish estimation and compensation after catching, so just can avoid because crosstalking between the subcarrier in frequency domain that carrier wave frequency deviation brings to carrier wave frequency deviation.These functions can utilize the PP autocorrelation performance similar with CP to finish, and also can regard PP as one section PN sequence, utilize in the cdma system ripe estimation and backoff algorithm based on the catching of PN sequence, carrier wave frequency deviation to finish.Here only provide that a kind of and CP similarly catches, Nonlinear Transformation in Frequency Offset Estimation and backoff algorithm.

Suppose that a series of sampled points that receiver is received are: R={r ₀, r ₁... r _i..., set a length of window L _W, in window, postpone to slide relevant to receiving sampled point.L _WCan equal A, also can be greater than or less than A according to channel conditions.Postponing size is M+A.The output of correlator can be expressed as follows:

$\mathrm{corr}\left(k\right)=\frac{\underset{i=0}{\overset{L_W-1}{\mathrm{\&Sigma;}}}{r}_{k+i}{r}_{k+i-(m+A)}^{*}}{L_W},$ Subscript ^*Represent complex conjugate.

The original position of the PP suffix of the corresponding non-inhibit signal in position of the obvious relevant peaks of appearance, the PP prefix of inhibit signal get original position in the output sequence of correlator.If the position that relevant peaks occurs is k _PP, then the every sampled point phase place that causes owing to carrier wave frequency deviation rotates to be: =angle[corr (k _PP)]/(M+A), angle[x] representative plural x the phase angle.Receiving sequence be multiply by sequence { exp (j 0), exp (j 1), exp (j 2) ... exp (j i) ... } can correct carrier wave frequency deviation.This method for synchronous is still effective under the multipath channel of very severe, as Figure 11, shown in Figure 12.Wherein, Figure 11 postpones the output (being output as plural number, the mould of the plural number that draws, the i.e. envelope of output signal here) of correlator for PP-OFDM system receiving end.Unique difference of simulated conditions and following Fig. 9 that will say is to add that every sampling point rotates the carrier wave frequency deviation and the noiseless of 1.3 radians.The correlator length of window equals guard interval.Figure 12 is carrier wave frequency deviation valuation output, the same Figure 11 of simulated conditions.As seen from the figure, the corresponding carrier wave frequency deviation valuation output of each relevant peaks, output valve conforms to every sampling point 1.3 radians of presetting, why some point upward has a little bias to be with 1.3 because the channel condition that uses is very abominable herein, the maximum delay expansion has reached 9/10 of guard interval, cause some unknown OFDM symbol in the correlation window, relevant output is caused interference.

As shown in Figure 9, be PP-OFDM of the present invention and CP-OFDM, the contrast of ZP-OFDM error performance.Each OFDM symbol contain 1024 subcarriers, subcarrier spacing 4kHz, guard interval long for the OFDM symbol 1/4, data symbol adopts QPSK modulation, gray mappings, coding, pilot tone adopt the BPSK modulation.Per two PP OFDM intersymbols have only a naked OFDM symbol, and per 8 OFDM symbols constitute a complete emission circulation, and this is by the arrangement decision of pilot frequency locations:

1,17,33...1009 the pilot frequency locations subscript of OFDM symbol:0:

5,21,37...1013 the pilot frequency locations subscript of OFDM symbol:2:

9,25,41...1017 the pilot frequency locations subscript of OFDM symbol:4:

13,29,45...1021 the pilot frequency locations subscript of OFDM symbol:6:

The union formation frequency domain upper density of four kinds of pilot tone patterns is 1/4 pilot tone, to make full use of 1/4 long guard interval.

Channel is 200 footpath WSSUS models, and maximum delay is 9/10 of guard interval, and rms delay is the 1/log (10) of maximum delay.Channel remains unchanged in 8 OFDM symbol times, but separate between different per 8 OFDM symbol times.

The frequency domain correlation function of ideal synchronisation, carrierfree frequency deviation, channel is known, noise power is known, maximum delay is known for receiving end, channel estimating adopts the MMSE interpolation, ZP-OFDM and PP-OFDM all adopt block MMSE equilibrium, and CP-OFDM adopts frequency domain to handle.

Data symbol power is 1, and frequency pilot sign power is 4, and this is the best power allocative decision for three kinds of systems under this simulated conditions that finds by a large amount of emulation.

As shown in figure 10, be PP-OFDM of the present invention and CP-OFDM, ZP-OFDM channel estimating MSE performance comparison.Simulated conditions is the same.

Claims (10)

1, a kind of orthogonal frequency division multiplexing communication method that uses preceding suffix signal is characterized in that, described preceding suffix signal obtains like this:

In OFDM frequency domain frame piece, place some modulated data symbols, all the other place the known frequency pilot sign of receiving terminal, OFDM frequency domain frame piece is uniformly-spaced evenly extracted, obtain a new frequency domain frame piece, with the data symbol zero setting in this new frequency domain frame piece, frequency pilot sign remains unchanged, and then this new frequency domain frame piece amplitude is carried out convergent-divergent and carries out reverse discrete fourier transform (IDFT) again, and multiply by the frequency shift signal corresponding with extracting original position.

2, the orthogonal frequency division multiplexing communication method that uses preceding suffix signal according to claim 1, it is characterized in that, the OFDM symbol of this method transmission has two kinds, promptly directly carries out OFDM symbol that IDFT obtains and OFDM symbol by OFDM frequency domain frame piece and is conjugated in the symbol that constitutes together before and after adding it.

3, the orthogonal frequency division multiplexing communication method that uses preceding suffix signal according to claim 2, it is characterized in that, when sewing the symbol transmission of composition before and after described OFDM symbol adds, OFDM frequency domain frame piece is carried out the IDFT conversion, make it become the time domain OFDM symbol that can in channel, transmit, and before and after this OFDM symbol, add described before suffix signal.

4, the orthogonal frequency division multiplexing communication method that uses preceding suffix signal according to claim 1, it is characterized in that, the described symbol that carries out from OFDM frequency domain frame piece is regarded all symbols in the OFDM frequency domain frame piece as end to end annular closed symbol sebolic addressing when extracting, symbolic number in the OFDM frequency domain frame piece can be extracted at interval and divide exactly, extract not necessarily first sign-on from OFDM frequency domain frame piece of original position, divide exactly but the total number of symbols before the original position can be extracted the interval.

According to claim 1 or the 4 described orthogonal frequency division multiplexing communication methods that use preceding suffix signal, it is characterized in that 5, the described symbol that carries out from OFDM frequency domain frame piece is when extracting, the frequency pilot sign of extraction is The more the better.

6, the orthogonal frequency division multiplexing communication method that uses preceding suffix signal according to claim 1 is characterized in that, the described zoom factor k that new frequency domain frame piece amplitude is carried out convergent-divergent calculates like this:

If contain M symbol in each OFDM frequency domain frame piece, the extraction space-number is G, contain X OFDM symbol altogether in a certain OFDM symbol time sequence, Y the OFDM symbol of sewing before and after having wherein arranged, all the other are naked OFDM symbol, and the power of each data subcarrier in the OFDM symbol of each the data symbol correspondence in the OFDM frequency domain frame piece is Power _D, the power of each pilot sub-carrier is Power _P, the pilot sub-carrier number that the OFDM symbol of sewing before and after Y has contains respectively is: P ₀, P ₂P _Y-1, the pilot sub-carrier number that Y contains respectively during front and back are sewed is: Q ₀, Q ₁Q _Y-1, generate the computing formula that y sews used zoom factor k to front and back and be:

$k=\sqrt{\frac{\underset{y=0}{\overset{Y-1}{\mathrm{\&Sigma;}}}{P}_y+\frac{{\mathrm{Power}}_D}{{\mathrm{Power}}_P}[\mathrm{XM}-\underset{y=0}{\overset{Y-1}{\mathrm{\&Sigma;}}}{P}_y]}{\mathrm{XG}{Q}_y}}.$

7, the orthogonal frequency division multiplexing communication method that uses preceding suffix signal according to claim 1, it is characterized in that, the OFDM symbol of sewing before and after described having can be used for channel estimating double as carrying simultaneously data, channel can reduce its emission frequency when stablizing, can strengthen its emission frequency when channel variation is very fast.

8, the orthogonal frequency division multiplexing communication method that uses preceding suffix signal according to claim 1 is characterized in that, described data symbol modulation system can be any in BPSK, QPSK, 16QAM, the 64QAM modulation system; The frequency pilot sign modulation system is the BPSK modulation.

9, the orthogonal frequency division multiplexing communication method that uses preceding suffix signal according to claim 1, it is characterized in that, this method also comprises, the receiver end PP that is concerned with adds closing operation, this is operating as: with that segment signal and OFDM symbol initial and preceding suffix signal isometric that segment signal addition isometric with preceding suffix signal after the ending of OFDM symbol, the mixed signal that sew the OFDM symbol that the formation circulation is complete and the complete front and back of circulation of zero padding, this mixed signal is carried out discrete fourier transform (DFT), can make the frequency pilot sign in the former OFDM frequency domain frame piece be strengthened by equivalence, with obtain the pilot frequency locations place more precise channels estimate, thereby improve whole channel estimated accuracy; Utilize the result of this channel estimating, to sew through the front and back after the channel at receiving terminal and to deduct, obtain time domain and do not have the naked OFDM symbol of crosstalking, then this naked OFDM symbol is carried out block least mean-square error or ZF (block MMSE/ZF) equilibrium, finally obtain valuation, finish transmission of Information data symbol in the OFDM frequency domain frame piece.

10, the orthogonal frequency division multiplexing communication method that uses preceding suffix signal according to claim 9, it is characterized in that, receiving terminal is at first caught OFDM symbol head before the PP that is concerned with adds closing operation, afterwards carrier wave frequency deviation is estimated and compensated, wherein, the autocorrelation performance of suffix signal before utilizing, can adopt catching of the Cyclic Prefix that utilizes among the similar CP-OFDM, Nonlinear Transformation in Frequency Offset Estimation and backoff algorithm are finished, also front and back can be sewed and regard one section PN sequence as, can utilize catching ripe in the cdma system based on the PN sequence, the estimation and the backoff algorithm of carrier wave frequency deviation are finished.

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