CN101364966B - Time-domain channel estimation method for MIMO OFDM downlink system - Google Patents

Time-domain channel estimation method for MIMO OFDM downlink system Download PDF

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CN101364966B
CN101364966B CN2008101413612A CN200810141361A CN101364966B CN 101364966 B CN101364966 B CN 101364966B CN 2008101413612 A CN2008101413612 A CN 2008101413612A CN 200810141361 A CN200810141361 A CN 200810141361A CN 101364966 B CN101364966 B CN 101364966B
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ofdm symbol
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CN101364966A (en
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杨雷
王丹
丁喆
韩丰
曹哲
徐迎曦
徐美玉
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Henan University of Science and Technology
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Abstract

The invention relates to a time domain channel estimation method of a multiple-input multiple-output orthogonal frequency-division multiplexing down system. A pilot frequency symbol sequence using orthogonal virtual pilot frequency symbol and code domain is assumed to be used; firstly, a receiving terminal estimates the frequency response of each sub-channel at the actual pilot frequency symbol sub-carrier; then, the channel estimation for the virtual pilot frequency symbol sub-carrier is obtained through the linear interpolation of channel estimation of adjacent symbols used for orthogonal frequency division; the received symbol is re-constructed by utilizing the virtual pilot frequency symbol and the channel estimation thereof, the impulse response estimation of each sub-channel is obtained by ranking the received symbol of the actual pilot frequency symbol sub-carrier in ascending order according to the index value of the sub-carrier and then applying the least square method for time domain regularization, and the channel estimation of all the pilot frequency symbol sub-carriers is obtained after partial Fourier transformation; and finally, the channel frequency response of each user data symbol sub-carrier is obtained through the linear interpolation of channel estimation of the pilot frequency symbol sub-carrier. The invention has the advantages that the channel estimation precision is high, and larger quantity of transmitting antenna can be supported.

Description

The time-domain channel estimating method of MIMO OFDM downlink system
Technical field
The present invention relates to the time-domain channel estimating method of a kind of MIMO OFDM (MIMO OFDMA) downlink system, be specifically related to a kind ofly use the method for estimation of subcarrier (PUSC) symbolic construction, belong to field of wireless communications systems based on part in the IEEE802.16e standard.
Background technology
In recent years, the broadband wireless technical development is swift and violent, and WiMAX becomes the focus that wireless communication arena is paid close attention to gradually.WiMAX is the wireless access wide band technology based on the IEEE802.16 series standard, supports fixing, nomadic, portable and mobile entirely four kinds of application scenarioss.Wherein mobile broadband wireless inserts air-interface standard 802.16e and relies on its ambulant support, high-speed data service and low cost, is considered as the wireless broad band technology of future generation that can contend with 3G by industry.And OFDM (OFDMA) has become the core technology of IEEE802.16e physical layer, and wherein a plurality of users are transmit information data simultaneously.On the other hand, multiple-input, multiple-output (MIMO) technology and OFDMA system are combined and can provide higher power system capacity and message transmission rate for wireless communication system.
Usually, channel information is extremely important for communication system, realizes coherent detection and self adaptation distribution because it can be assisted.Yet this information is unknown at receiving terminal, and receiver need be estimated it for this reason, and the quality of channel estimating greatly affects the performance of whole system.At present, the channel estimating of multi-carrier MIMO system is generally finished at frequency domain, also can finish in time domain.Because received signal is the signal stack of a plurality of transmitting antennas, there is interference in signal between the different transmit antennas, therefore also need consider how to design sequence of pilot symbols to avoid antenna interference.Usually, avoiding and can realizing by designing the orthogonal guide frequency symbol sebolic addressing in time domain, frequency domain or sign indicating number territory of many inter-antenna interference also be that different antennae can adopt the mode of time-division to send (identical or different) sequence of pilot symbols; Perhaps different antennae uses the different sub carrier location sets to send (identical or different) sequence of pilot symbols; Perhaps the frequency pilot sign of different antennae takies identical time frequency unit, by using quadrature between mutually orthogonal sign indicating number realization antenna.Yet, because the number of pilot symbols that the IEEE802.16ePUSC symbolic construction distributes is considerably less, so if under MIMO OFDMA system, use the frequency domain least square channel estimation methods of frequency domain quadrature (being frequency division) sequence of pilot symbols, can cause bigger evaluated error, and with perfect channel under to compare performance loss bigger.In pertinent literature, sign indicating number territory orthogonal guide frequency symbol sebolic addressing time domain least square channel estimation methods appearred adopting, this method estimated accuracy is higher, but the sequence of pilot symbols that needs each transmitting antenna relatively the time shifting amount of the sequence of pilot symbols of first transmitting antenna between channel length and each transmitting antenna pilot tone number are divided by number of transmit antennas, so under some channel circumstance, can't support more number of transmit antennas.
Summary of the invention
The objective of the invention is at the deficiencies in the prior art, a kind of time-domain channel estimating method of MIMO OFDM downlink system is provided,, support more number of transmit antennas to obtain more excellent channel estimating performance.
For finishing above-mentioned task, the method that the invention provides has been used the virtual pilot frequency symbol at the PUSC of IEEE802.16e symbolic construction, think that promptly the frequency pilot sign of even number (odd number) OFDM symbol is the virtual pilot frequency symbol of odd number (even number) OFDM symbol, increased the effective number of pilot symbols of system; Receiving terminal at first obtains each dual-mode antenna the least square method channel frequency response at actual pilot symbol subcarrier place is estimated; Then, the channel frequency response at virtual pilot frequency symbol subcarrier place is obtained by the channel frequency response linear interpolation at same sub-carrier place in the adjacent OFDM symbol in each OFDM symbol; Utilize the channel frequency response at virtual pilot frequency symbol subcarrier place and the frequency domain receiving symbol at this subcarrier place of virtual pilot frequency symbol reconstruct again, the receiving symbol at associating actual pilot symbol subcarrier place is used time domain canonical criterion of least squares after by ascending order sub-carrier indices value sequence arrangement again and is obtained each subchannel time domain impulse response and estimate that the channel frequency response that obtains all frequency pilot sign subcarrier places behind the part Fourier transform is estimated; At last, the channel frequency response at each user's corresponding data symbol subcarrier place estimates that by the channel frequency response at frequency pilot sign subcarrier place linear interpolation obtains.
Corresponding with said method, the invention provides concrete steps:
1) each transmitting antenna of transmitting terminal carries out data symbol and the mapping of frequency pilot sign subcarrier according to the symbolic construction of down link PUSC among the IEEE802.16e, forms an OFDM symbol; Concrete grammar is: all useful subcarriers in each OFDM symbol (getting rid of protection subcarrier and direct current subcarrier) are divided into several bunches, bunch number depend on the size of Fourier transform, each bunch contains 14 adjacent sub-carriers, wherein there are two subcarriers to be used to place frequency pilot sign, even number OFDM symbol is different with the frequency pilot sign sub-carrier positions of odd number OFDM symbol, and remaining subcarrier is used for different user and carries out the data symbol transmission with the form of frequency division multiple access;
2) each transmitting antenna of transmitting terminal uses the virtual pilot frequency symbol in each OFDM symbol, think that promptly frequency pilot sign is a virtual pilot frequency symbol in odd number or the even number OFDM symbol in even number or the odd number OFDM symbol, all transmitting antennas use identical frequency resource, and the individual frequency pilot sign of new sequence of pilot symbols p ' of actual pilot symbol sebolic addressing and the formation of virtual pilot frequency symbol sebolic addressing is in i each OFDM symbol of transmitting antenna X i a ( k p ′ a ) = c i ( p ′ ) = c ( p ′ ) e - jπp ′ ( i - 1 ) Δt N p , P '=1 wherein ..., 2N p, time shift Δ t satisfies L≤Δ t≤2N p/ M t, L is the exponent number of all subchannels, M tBe the sum of transmitting antenna, N pBe the actual frequency pilot sign number of using in each OFDM symbol,
Figure G2008101413612D00032
For actual pilot symbol in each OFDM symbol and virtual pilot frequency symbol being occupied the individual element of p ' after the sub-carrier indices value is arranged by ascending order, c (p ') is the individual frequency pilot sign of p ' of first transmit antennas emission;
3) OFDM symbol at each transmitting antenna place is made inverse Fourier transform, insert Cyclic Prefix then after transmitting antenna sends;
4) each reception antenna of receiving terminal need carry out Fourier transform to the received signal behind the removal Cyclic Prefix, obtain OFDM symbol, extract the symbol of actual pilot symbol sub-carrier positions in even number OFDM symbol and the odd number OFDM symbol according to the subcarrier mapped mode of transmitting terminal use respectively through the wireless channel transmission;
5) by the frequency pilot sign of the known transmitting terminal of receiving terminal and step 4) together, calculate of the least-squares estimation of each dual-mode antenna to actual pilot symbol subcarrier place's channel frequency response in each OFDM symbol;
6) the channel frequency response at virtual pilot frequency symbol subcarrier place is obtained by the channel frequency response linear interpolation at same sub-carrier place in the adjacent orthogonal frequency division multiplexing symbol in each OFDM symbol;
7) utilize in each OFDM symbol virtual pilot frequency symbol and the step 6) frequency domain receiving symbol at reconstruct virtual pilot frequency symbol subcarrier place together, the frequency domain receiving symbol at associating actual pilot symbol subcarrier place together, by the sub-carrier indices value { k p ′ a , p ′ = 1 , · · · , 2 N p } After arranging, ascending order obtains the frequency domain receiving symbol sequence at all frequency pilot sign subcarrier places;
8) the frequency domain receiving symbol sequence and the step 2 of all pilot frequency symbol positions that obtain by step 7)) new sequence of pilot symbols together, calculate the right time domain channel impulse response of each dual-mode antenna based on time domain canonical least-squares estimation criterion and estimate, behind the part Fourier transform, obtain the final channel frequency response estimation at all frequency pilot sign subcarrier places in the OFDM symbol then;
9) last, the channel frequency response at each user's corresponding data symbol subcarrier place estimates that by the channel frequency response at frequency pilot sign subcarrier place linear interpolation obtains.
The inventive method has increased the spendable number of pilot symbols of system by using the virtual pilot frequency symbol, and reconstruct the frequency domain receiving symbol at virtual pilot frequency symbol subcarrier place, make the number of transmit antennas of system's support double.Based on the frequency domain receiving symbol sequence of all sequence of pilot symbols and respective sub position, use the time domain criterion of least squares and estimate the channel impulse response that each dual-mode antenna is right, and used the method for canonical to improve channel estimated accuracy further.Whole process need not channel correlation properties information, and the time domain canonical least square method of use can make the minimum frequency division pilot tone least square frequency domain method of complexity of the present invention and amount of calculation compare slightly to be increased.Yet, the inventive method is owing to used the more pilot symbol and used the canonical method to overcome the inhomogeneities of pilot frequency symbol position, so obtained higher estimated accuracy than conventional method, and can support more number of transmit antennas, made it be applicable to actual application scenarios more.
The amount of calculation of the inventive method mainly comes from the calculating of the matrix inversion item that time domain canonical least-squares estimation device contains.In order to analyze for simplicity, the present invention is the high-order of the required multiplication number of times of each method relatively only.Because the calculating of matrix inversion item and channel are irrelevant among the present invention, and only depend on sequence of pilot symbols and the set of sub-carrier indices value accordingly that actual pilot symbol and virtual pilot frequency symbol form, therefore it is invariable and can be received machine known, therefore this can be precomputed, so the amount of calculation of this part can be ignored.Above-mentioned matrix inversion item calculated in advance multiply by frequency domain receiving symbol sequence after good and can obtain channel impulse response estimation, and the amount of calculation of this part be O (
Figure G2008101413612D0005102009QIETU
) rank.Traditional frequency division pilot tone frequency domain least square method so complexity is minimum, can be O (N owing to only need simple multiplication and division computing p) rank.In addition, traditional sign indicating number divides amount of calculation and the present invention of pilot tone time domain least square method similar, its complexity also be O ( ) rank.So the inventive method is compared with frequency division pilot tone frequency domain least square method, though complexity slightly increases, estimated performance has obtained great raising; Compare with sign indicating number branch pilot tone time domain least square method, complexity is identical, but can support more number of transmit antennas.
Description of drawings
Fig. 1 is the FB(flow block) of channel estimation methods of the present invention;
Fig. 2 is actual pilot symbol of the present invention and the distribution map of virtual pilot frequency symbol in successive clusters;
Fig. 3 is conventional channel method of estimation and channel estimation methods bit error rate performance of the present invention comparison under the 4X4PB mimo channel.
Embodiment
Below in conjunction with drawings and Examples technical scheme of the present invention is further described.
Consider single user OFDMA downlink transmission system of four transmit antennas and four reception antennas, its communication environment is to select comparatively serious PB channel frequently, user's translational speed is 3km/h, carrier frequency is that 2.5GHz and system bandwidth are 10MHz, the Fourier transform size is 1024, and circulating prefix-length is 128.Background noise is obeyed the being added with property Gaussian Profile of zero-mean.Data symbol is to be that 1/2 turbo coding, brachymemma, intra-frame interleaving and QPSK constellation mapping form by binary number through code check.Adopt flow process that the inventive method carries out channel estimating as shown in Figure 1, concrete implementation step is as follows:
1) each transmitting antenna of transmitting terminal carries out data symbol and the mapping of frequency pilot sign subcarrier according to the symbolic construction of down link PUSC among the IEEE802.16e, forms an OFDM symbol.Concrete grammar is: all useful subcarriers in each OFDM symbol (getting rid of protection subcarrier and direct current subcarrier) are divided into 60 bunches; each bunch contains 14 adjacent sub-carriers; wherein there are two subcarriers to be used to place frequency pilot sign; the placement principle is: even number OFDM symbol is different with the frequency pilot sign sub-carrier positions of odd number OFDM symbol; actual pilot symbol in the even number OFDM symbol in each bunch lays respectively at the 5th and the 9th subcarrier, and forms the set that frequency pilot sign in all bunches occupies the sub-carrier positions index and be k e = { k 1 e , · · · , k p e , · · · , k N p e } ; Actual pilot symbol in the odd number OFDM symbol in each bunch lays respectively at the 1st and the 13rd subcarrier, and forms the set that frequency pilot sign in all bunches occupies the sub-carrier positions index and be k o = { k 1 o , · · · , k p o , · · · , k N p o } . At last, remaining subcarrier is used for different user and carries out data symbol transmission with the form of frequency division multiple access;
2) each transmitting antenna of transmitting terminal uses the virtual pilot frequency symbol in each OFDM symbol, think that promptly frequency pilot sign is a virtual pilot frequency symbol in odd number (even number) the OFDM symbol in even number (odd number) the OFDM symbol, make number of pilot symbols increase to the twice of not using the virtual pilot frequency symbol scheme originally.So, set k oSub-carrier positions set for virtual pilot frequency symbol in the even number OFDM symbol; Set k eSub-carrier positions set for virtual pilot frequency symbol in the odd number OFDM symbol.To occupy the set of sub-carrier positions be k for actual pilot symbol and virtual pilot frequency symbol in each OFDM symbol a=sort{k e∪ k o, wherein, " ∪ " expression set and operation, the element during " sort " expression will be gathered is arranged by ascending order.Because all transmitting antennas use identical frequency resource, interference between antenna can be removed by the sign indicating number territory quadrature of sequence of pilot symbols, so the individual frequency pilot sign of new sequence of pilot symbols p ' that actual pilot symbol sebolic addressing and virtual pilot frequency symbol sebolic addressing form in each OFDM symbol of i transmitting antenna is satisfied X i a ( k p ′ a ) = c i ( p ′ ) = c ( p ′ ) e - jπp ′ ( i - 1 ) Δt N p , P '=1 wherein ..., 2N p, time shift Δ t satisfies L≤Δ t≤2N p/ M t, L is the exponent number upper bound of all subchannels, M tBe the transmitting antenna sum, N pBe the actual frequency pilot sign number of using in each OFDM symbol, Arrange set k in back for actual pilot symbol and virtual pilot frequency symbol in each OFDM symbol being occupied the sub-carrier indices value by ascending order aIn the individual element of p ', c (p ') is the individual frequency pilot sign of p ' of first transmitting antenna.Owing to used the virtual pilot frequency symbol, so effective number of pilot symbols of each transmitting antenna increases to original twice, so the antenna number of the inventive method support is yard twice of territory pilot tone time domain least square method;
3) the OFDM symbol at each transmitting antenna place is done contrary N point Fourier conversion, insert Cyclic Prefix then after transmitting antenna sends.P frequency pilot sign of i transmitting antenna even number and odd number OFDM symbol is expressed as respectively
Figure G2008101413612D00074
With
Figure G2008101413612D00075
P=1 wherein ..., N pIn addition, Be assumed to be the virtual pilot frequency symbol of neighbouring even-numbered OFDM symbol, and Be assumed to be the virtual pilot frequency symbol of adjacent odd number OFDM symbol, continuously the pilot distribution structure in several bunches is as shown in Figure 2 for it;
4) each reception antenna of receiving terminal need carry out the conversion of N point Fourier to the received signal behind the removal Cyclic Prefix, obtain the OFDM symbol through wireless channel transmission, the subcarrier mapped mode that uses according to transmitting terminal extracts respectively that actual pilot symbol subcarrier place frequency domain receiving symbol sequence is in the OFDM symbol R j n = Σ i = 1 M i diag { X i n } F ~ n h ji n + W j n , J=1 ..., M rIf " n " is even number constantly, so X i n = X i e = [ X i e ( k 1 e ) , · · · , X i e ( k p e ) , · · · , X i e ( k N p e ) ] T , The element of part fourier transform matrix [ F ~ n ] p , l = [ F ~ e ] p , l = e - j 2 πl k p e N , P=1 ..., N p, l=0 ..., L-1; If odd number OFDM symbol is constantly, X i n = X i o = [ X i o ( k 1 o ) , · · · , X i o ( k p o ) , · · · , X i o ( k N p o ) ] T , [ F ~ n ] p , l = [ F ~ o ] p , l = e - j 2 πl k p o n , p＝1，…，N p，l＝0，…，L-1。Wherein, " diag{} " expression subtend is measured the diagonal matrix operation,
Figure G2008101413612D00086
I transmitting antenna be to the subchannel impulse response of j reception antenna when representing n OFDM symbol, and suppose that all subchannels have identical channel exponent number L,
Figure G2008101413612D00087
Be the multiple Gaussian noise of j reception antenna place zero-mean, its statistical property does not change with the variation of " n " constantly;
5) by the frequency pilot sign of the known transmitting terminal of receiving terminal and step 4) together, calculate of the least-squares estimation of each dual-mode antenna to actual pilot symbol subcarrier place's channel frequency response in n the OFDM symbol
Figure G2008101413612D00088
I=1 ..., M t, j=1 ..., M r
6) the channel frequency response at virtual pilot frequency symbol subcarrier place is obtained by the channel frequency response linear interpolation at same sub-carrier place in the adjacent OFDM symbol in each OFDM symbol, and promptly the channel frequency response of virtual pilot frequency symbol subcarrier is estimated as in the even number OFDM symbol
Figure G2008101413612D00089
And the channel frequency response of virtual pilot frequency symbol subcarrier is estimated as in the odd number OFDM symbol
7) utilize in each OFDM symbol virtual pilot frequency symbol and step 6) together the frequency domain receiving symbol at reconstruct virtual pilot frequency symbol subcarrier place be: With
Figure G2008101413612D000812
Wherein, i=1 ..., M t, j=1 ..., M rAnd p=1 ..., N pThen will
Figure G2008101413612D0008102515QIETU
Frequency domain receiving symbol sequence with actual pilot symbol subcarrier place
Figure G2008101413612D000813
Together, by the sub-carrier indices value { k p ′ a , p ′ = 1 , · · · , 2 N p } After arranging, ascending order obtains the frequency domain receiving symbol sequence at all frequency pilot sign subcarrier places
8) the frequency domain receiving symbol sequence and the step 2 of all pilot frequency symbol positions that obtain by step 7)) new sequence of pilot symbols obtain new received signal Mathematical Modeling: R ‾ j n = Ah j n + W j n , J= 1..., M r, wherein, matrix A = [ diag { X 1 a } F - , · · · , diag { X M i a } F - ] , [ F - ] p ′ , l = e - j 2 πl k p ′ a N Be the element of part fourier transform matrix, p '=1 ..., 2N p, l=0 ..., L-1, the channel vector of n the OFDM symbol in reception antenna j place is h j n = h 11 n T · · · h M i 1 n T T . The time domain channel impulse response that calculates reception antenna j based on above-mentioned model application time domain canonical least-squares estimation criterion is estimated as h ~ j n = ( A H A + α I LM i ) - 1 A H R - j n , Wherein parameter alpha is minimum number, and its effect is to alleviate the influence of the error of ill-condition matrix inversion to channel estimating performance.This is not owing to the pilot sub-carrier position is not to be spacedly distributed, and also there is a large amount of protection subcarriers in entire spectrum, so A HThough A is reversible in theory, can present ill-condition, this will influence the accuracy of channel estimating.Then, the final estimation of all frequency pilot sign subcarrier place channel frequency responses can obtain through the part Fourier transform:
Figure G2008101413612D00097
Symbol wherein
Figure G2008101413612D00098
Expression kroneck convolution;
9) last, the channel frequency response at the data symbol subcarrier place that each user uses estimates that by the channel frequency response at frequency pilot sign subcarrier place linear interpolation obtains.
Above-mentioned channel estimation process, by using the virtual pilot frequency symbol to increase the quantity of the effective frequency pilot sign of system, therefore system can support more number of transmit antennas, by using time domain canonical least square rule to estimate channel impulse response, has improved performance for estimating channel effectively simultaneously.Whole process is not used channel correlation properties knowledge and complicated matrix manipulation, therefore use channel estimation methods of the present invention to calculate frequency domain equalizer coefficients, not only can satisfy certain estimated accuracy, and can support more number of transmit antennas, be fit to the substandard communication environment of IEEE802.16e more.
Fig. 3 is the comparative result of bit error rate performance under channel estimation methods, frequency division pilot tone frequency domain least square channel estimation methods and the known perfect channel information of the inventive method employing.Receiver has adopted simple zero forcing equalization method to resist the intersymbol interference that wireless fading channel produces.Traditional sign indicating number branchs time domain least square channel estimation methods is because the L≤Δ t≤N that can not satisfy condition when constructing pilot frequency sequence p/ M tSo, under the system environments of four transmit antennas, can't use.The channel frequency response that each user uses data symbol subcarrier place is obtained by the channel frequency response linear interpolation at the frequency pilot sign subcarrier place that estimates.Suppose to become when channel is, but in an OFDM symbol, keep constant, promptly satisfy the piece fading characteristic.As can be seen, the bit error rate performance of channel estimation methods of the present invention obviously is better than traditional frequency division pilot tone frequency domain least square channel estimation methods from the figure, and is 10 in the error rate -3In time, compared with perfect channel information, and the performance loss of about 3dB is only arranged.Channel estimation methods of the present invention does not need all to carry out complicated matrix operation at every turn, need not to obtain in advance the correlation properties information of channel yet, has obtained certain estimated accuracy, and has supported more number of transmit antennas, is easy to practicability.
Although the present invention is described in conjunction with specific embodiment, for a person skilled in the art, can under the situation that does not deviate from the spirit or scope of the present invention, make amendment or change.Such modifications and variations all should be considered within scope of the present invention and additional claims scope.

Claims (3)

1. the time-domain channel estimating method of a MIMO OFDM downlink system is characterized in that, this method step is as follows:
1) use subcarrier PUSC symbolic construction to use the virtual pilot frequency symbol in the part of IEEE 802.16e, the frequency pilot sign of setting even number OFDM symbol is the virtual pilot frequency symbol of odd number OFDM symbol, the frequency pilot sign of odd number OFDM symbol is the virtual pilot frequency symbol of even number OFDM symbol, the effective number of pilot symbols of increase system;
2) receiving terminal at first obtains the least square channel frequency response estimation of each dual-mode antenna to actual pilot symbol subcarrier place;
3) the channel frequency response at virtual pilot frequency symbol subcarrier place is obtained by the channel frequency response linear interpolation at same sub-carrier place in the adjacent OFDM symbol in each OFDM symbol;
4) utilize the channel frequency response at virtual pilot frequency symbol subcarrier place and the frequency domain receiving symbol at this subcarrier place of virtual pilot frequency symbol reconstruct, the receiving symbol at associating actual pilot symbol subcarrier place is used time domain canonical criterion of least squares after by ascending order sub-carrier indices value sequence arrangement and is obtained each subchannel time domain impulse response and estimate that the channel frequency response that obtains all frequency pilot sign subcarrier places behind the part Fourier transform is estimated;
5) last, the channel frequency response at each user's corresponding data symbol subcarrier place estimates that by the channel frequency response at frequency pilot sign subcarrier place linear interpolation obtains.
2. the time-domain channel estimating method of a MIMO OFDM downlink system is characterized in that, these method concrete steps are as follows:
1) each transmitting antenna of transmitting terminal uses subcarrier PUSC symbolic construction to carry out data symbol and the mapping of frequency pilot sign subcarrier according to downlink portion among the IEEE 802.16e, forms an OFDM symbol;
2) each transmitting antenna of transmitting terminal uses the virtual pilot frequency symbol in each OFDM symbol, frequency pilot sign is a virtual pilot frequency symbol in the odd number OFDM symbol in the even number OFDM symbol, frequency pilot sign is a virtual pilot frequency symbol in the even number OFDM symbol in the odd number OFDM symbol, all transmitting antennas use identical frequency resource, and the individual frequency pilot sign of new sequence of pilot symbols p ' of actual pilot symbol sebolic addressing and the formation of virtual pilot frequency symbol sebolic addressing is in i each OFDM symbol of transmitting antenna
Figure FSB00000297491100021
P '=1 wherein ..., 2N p, time shift Δ t satisfies L≤Δ t≤2N p/ M t, L is the exponent number of all subchannels, M tBe the sum of transmitting antenna, N pBe the actual frequency pilot sign number of using in each OFDM symbol,
Figure FSB00000297491100022
For actual pilot symbol in each OFDM symbol and virtual pilot frequency symbol being occupied the individual element of p ' after the sub-carrier indices value is arranged by ascending order, c (p ') is the individual frequency pilot sign of p ' of first transmit antennas emission;
3) OFDM symbol at each transmitting antenna place is made inverse Fourier transform, insert Cyclic Prefix then after transmitting antenna sends;
4) each reception antenna of receiving terminal need carry out Fourier transform to the received signal behind the removal Cyclic Prefix, obtain OFDM symbol, extract the symbol of actual pilot symbol sub-carrier positions in even number OFDM symbol and the odd number OFDM symbol according to the subcarrier mapped mode of transmitting terminal use respectively through the wireless channel transmission;
5) by the frequency pilot sign of the known transmitting terminal of receiving terminal and step 4) together, calculate of the least-squares estimation of each dual-mode antenna to actual pilot symbol subcarrier place's channel frequency response in each OFDM symbol;
6) the channel frequency response at virtual pilot frequency symbol subcarrier place is obtained by the channel frequency response linear interpolation at same sub-carrier place in the adjacent orthogonal frequency division multiplexing symbol in each OFDM symbol;
7) utilize in each OFDM symbol virtual pilot frequency symbol and the step 6) frequency domain receiving symbol at reconstruct virtual pilot frequency symbol subcarrier place together, the frequency domain receiving symbol at associating actual pilot symbol subcarrier place together, by the sub-carrier indices value
Figure FSB00000297491100031
After arranging, ascending order obtains the frequency domain receiving symbol sequence at all frequency pilot sign subcarrier places;
8) the frequency domain receiving symbol sequence and the step 2 of all pilot frequency symbol positions that obtain by step 7)) new sequence of pilot symbols together, calculate the right time domain channel impulse response of each dual-mode antenna based on time domain canonical least-squares estimation criterion and estimate, behind the part Fourier transform, obtain the final channel frequency response estimation at all frequency pilot sign subcarrier places in the OFDM symbol then;
9) last, the channel frequency response at each user's corresponding data symbol subcarrier place estimates that by the channel frequency response at frequency pilot sign subcarrier place linear interpolation obtains.
3. method of estimation according to claim 2; it is characterized in that; the concrete grammar of step 1) is: will protect interior all the useful subcarriers of each outer OFDM symbol of subcarrier and direct current subcarrier to be divided into several bunches; each bunch contains 14 adjacent sub-carriers; wherein there are two subcarriers to be used to place frequency pilot sign; the frequency pilot sign sub-carrier positions of even number OFDM symbol and odd number OFDM symbol is different, and remaining subcarrier is used for different user and carries out the data symbol transmission with the form of frequency division multiple access.
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