WO2005022776A2

WO2005022776A2 - Communication method, communication system, and receiver

Info

Publication number: WO2005022776A2
Application number: PCT/JP2004/012670
Authority: WO
Inventors: Hiroshi Ochi; Shigenori Kinjo
Original assignee: Kitakyushu Foundation For The Advancement Of Industry, Science And Technology; Que-Wave Co., Ltd.
Priority date: 2003-08-27
Filing date: 2004-08-26
Publication date: 2005-03-10
Also published as: JP2006339686A; WO2005022776A3

Abstract

A communication method comprise an space-time block code(STBC)-processing step for dividing a transmit symbol sequence X into blocks and generating two mutually orthogonal symbol sequences XnA and XnB based on a symbol sequence Xn of each block, a transmitting step for modulating each of the symbol sequences XnA and XnB by an OFDM system and transmitting it by a transmitter diversity system; an OFDM demodulating step for demodulating a receive signal by applying discrete Fourier transform thereto, and generating a receive symbol sequence Rn, and an STBC demodulating step for demodulating a symbol sequence Xn' of each block by using a receive symbol sequence Rn for inverse matrix H-1 of transfer function matrix H, constituted based on a transfer function estimated for each block and for each sub-carrier by a prescribed estimation method, and by which the receive symbol sequence Rn is related to the symbol sequence Xn.

Description

DESCRIPTION

COMMUNICATION METHOD, COMMUNICATION SYSTEM, AND RECEIVER

Technical field The present invention relates to a data communication technology capable of suppressing the deterioration in error property caused by frequency-selective fading and time-selective fading.

BackgroundArt Particular problem in a broadband wireless communication in multi-paths environment is that frequency-selective fading by multi-paths causes channel quality to deteriorate. As a modulation system for suppressing the influence caused by multi-paths fading, a multi carrier transmission system is a conventionally well-known system. The multi-paths carrier transmission system has a characteristic that the multi-path fading has least influence on a narrow band sub-carrier. Therefore, by using such a characteristic, a frequency feature • of a communication line is suppressed to be low by dividing the transmission band into plural sub-carriers. As one of the multi carrier transmission systems, orthogonal frequency division multiplex (referred to as "OFDM" hereafter) for transmitting signals by using orthogonalized plural narrow band sub-carriers is frequently used at present. Meanwhile, in recent years, demand for mobile communication has been rapidly increasing. Reception of wireless signals on the side of a mobile object is largely affected by time-varying fading (time selective fading) , which is a temporally varying fading. As effective means for suppressing the time selective fading, conventionally, a transmitter diversity system has been used. In addition, in the transmitter diversity system, as one of the methods to compensate the lowering of an amplitude of a receive signal caused by fading, a method using space time block coding (referred to as "STBC" hereafter) is well-known (for example, please refer to Ref.l and Ref.2). Fig.11 is a block diagram illustrating the structure of a communication apparatus by the conventional OFDM-STBD system (cf . Ref.l). A transmitter 100 comprises an STBC encoder 101, serial parallel converters (referred to as "S/P converter" hereafter) 102a and 102b, inverse discrete Fourier transformers (referred to as ^λλIDFT" hereafter) 103a and 103b, parallel serial converters (referred to as "P/S converter" hereafter) 104a and 104b, transmitting antennas 105a and 105b, and a preamble generator 106. A transmit symbol sequence (x={..., x₂j, X2j₊ι, ...} which is transmitting data, is inputted in the STBC encoder 101 of the transmitter 100. Here, x_2j designates the 2j-th transmit symbol. The STBC encoder 101 divides the transmit symbol sequence X thus inputted into blocks of symbol numbers of M (M ≥ 2) . Then, the block number of each block thus obtained by division is defined as n, and the transmit symbol sequence belonging to the n-th block is designated by X_n. That is, the equation can be written as X={X_n} . Next, the STBC encoder 101 encodes the transmit symbol sequence thus divided into two symbol sequences x_n ^A and x_n ^B which are orthogonal to each other and expressed by Eq. (1) and Eq. (2) .

^■Λ- ⁼ {" ' ) ^23,11! ^x2₃+l,n, ^x2 +2,n: £2j+3,nj " ' "}

^■^ — I^{" ' "} ! ^!E2j 1,n^{) — X}2₃,n> ^X2₃+3,n> ~ ^x2₃+2,ni " ^'S

where, in the description of symbol X_2D+I, _n in each block, n expresses a block number, and 2j+l expresses a sub-carrier number in the block. Note that an encoding method of a transmitting_symbol sequence

X is not limited to the aforementioned method, but may be any method, provided that the symbol sequences X_n ^A and X_n ^B are orthogonal to each other. For example, in Ref.3, the encoding method represented by

Eq. (3) and Eq. (4) is employed.

^Λ _n ~ Y " ; ^x2 _<n, —^χ2j+l,n) ^x2j+2,n, — 2 +3,n> " ' = [ 2₃,n, - ^*2₃₊l_:n] i (³)

^n ⁼ {^*" )^a;2j+l,τi)^2j₎n!^a;2j+3_Jn)^:c2j+2,n!'-'}

Any one of the above-described encoding methods may be used for the symbol sequences X_n ^A and X_n ^B. Explanation will be given hereunder, based on the fact that the STBC encoder 101 encodes the symbol sequences by the encoding method expressed by Eq. (1) and Eq. (2). In addition, the combination of two symbols such as { ₂-,,_nf X₂₃₊i_m} is a subset of the symbol becoming an encoding processing unit during STBC, and the subset is referred to as "block" hereafter. In the STBC explained here, the number of symbols per block unit is two. However, in the STBC generally used, the number of symbols per block unit is not limited to two. In the S/P converters 102a and 102b, symbol sequences {X_nA} and {X_nB} are made to be parallel for each block, to generate M sub-carriers (see Fig.12) . In the IDFTs 103a and 103b, by applying IDFT to the inputted M sub-carriers, OFDM signals are generated. The OFDM signals are made to be serial by the P/S converters 104a and 104b, and transmitted from transmitting antennas 105a and 105b. Fig.12 is a view illustrating the form of the OFDM signal transmitted from a transmitter. In Fig.12 (a), the sub-carriers modulated in time and frequency region are shown by D. In Fig.12 (a) , ther,e are M sub-carriers, and the interval of the sub-carriers is shown by Δf_s. The symbol of the block number (time) in the 2j-th sub-carrier (frequency) can be written as x_2j,_n- Fig.12(b) illustrates the structure of each symbol. Each symbol is formed of a guard interval corresponding to time length T_G and FET interval corresponding to time length T_F. Thus, by providing the guard interval before the FET interval, the effect of the multi-path fading is reduced. Fig.13 is a block diagram illustrating the structure of a receiver of the conventional OFDM-STBC system (see Ref.l). The receiver 110 comprises a receiving antenna 111, a S/P converter 112, a discrete Fourier transformer (referred to as "DFT" hereafter) 113, a P/S converter 114, an STBC decoder 115, and a transmission path characteristic estimation part 116. > A receive signal received by the receiving antenna 111 is sampled by the S/P converter 112 and converted into M sub-carriers. The discrete Fourier transform is applied to the sub-carriers by the DFT 113, and the sub-carriers are then serialized by the P/S converter 114. Thus, the receive signal for n-th block expressed by R_n= { ... , r₂₃,_n, r_{2D +} ι, _n, - } is restored. A symbol sequence R_n is formed in such a way that signals are transmitted from the transmitting antennas 105a and 105b, received by the receiving antenna 111 though each transmission path, and superposed. The symbol sequence R_n can be written as Eq. (5) and Eq. (6) as follows: r₂₃,n = ^x2₃,nH£_Jtn + ^x +l,_nHi₃,n (5)

Here, H_2;),_n ^A is a transfer function related to the 2j-th sub-carrier of the n-th block of the transmission path leading to the receiving antenna 111 from the transmitting antenna 105a, and H_2;],_n ^B is the transfer function related to the 2j-th sub-carrier of the n-th block of the transmission pa h leading to the receiving antenna 111 from the transmitting antenna 105b. Note that in Eq. (5) and Eq. (6), a white-noise term is omitted. Here, in each transmission path, the transfer function related to the 2j-th sub-carrier and the transfer function related to the 2j+l-th sub-carrier adjacent thereto are supposed to be approximately the same value (multi-path fading is constant) . That is, it can be assumed that approximation H_2D , ^A=a^H_2:i + i, _n » H ₃,_n ^B ^i?H_{2:] +} ι,_n ^B is established. If it is so assumed, the symbols x₂₃,n and x₂₃₊i,_n can be restored by Eq. (7) and Eq. (8) . :> +l,n ,¹H^J-2->j. ,n) (7)

(^r2_j, Hi₃,_n + 1~2₃+l,nHi*_n) (8)

where, |H₂₃,_n ^Al» lH_2:),n^Bl can be obtained by the transmission path characteristic estimation part 116 in a following way (for example, see Ref.2). First, a preamble generator 106 of the transmitter 100 outputs a particular prescribed symbol sequence (preamble) . As the preamble, for example, a long preamble sequence that meets ARIB standard STD-T71 can be used (see Ref .4) . Here, the preambles C_n ^A and C_n ^B expressed by Eq. (9) and Eq. (10) are assumed to be generated. C« — {^c0,n, Cl, , C2,n, C3,_n, ^{• ■ •} , CM-2,n, C -l,n} (9) C_n — {^c0,n, —C ,_n, C2, , ~C3,n, ^{• ■ •} , C-M-2,n,- ~Cjtf-l.n} (10) The preambles C_n ^A and C_n ^B are transmitted in the same way as the transmitting symbol sequence. The symbol sequence

^•■■,r^c _M__{1 n}} of the preamble received by the receiver can be written as Eq. (11) and Eq. (12) in the same way as Eq. (5) and Eq. (6) .

where, approximation is made like H_2j A

+ 1 , n H 2]

H_{2: +} ι,n^B and if inequality is made like -2c_2] , _nc₂₃ + ι , _n ≠ O the estimate value of the transfer function of the transmission path H_2D,_n ^A _> H₂-_|,_n ^B is obtained by Eq. (13). Here, I^"~j is a designation mark for specifying the estimate value.

The transmission path characteristic estimation part 116 obtains the estimate value of the transfer function H_2;],n^A and H_2;),_n ^B by Eq. (12) . The STBC decoder 115 restores the symbols x₂j,n and X2j₊ι,n by Eq. (7) and Eq. (8), based on the estimate value.

(Prior Art) (Ref. 1) Japanese Patent Laid Open No.2002-344415 (Ref. 2) Japanese Patent Laid Open No.2002-118534 (Ref. 3) N.Ahmed and R.G. Baraniuk, "Asymptotic performance of transmit diversity via OFDM for multi-paths channels", Global Telecommunications Conference, 2002. GLOBECOM '02. IEEE, BWS-04-1, Nov. 2002 (Ref. 4) "Small-electric-power data communication system/Broad band mobile access system (CSMA)", Association of Radio Industries and Businesses, ARIB STD-T71, December 14, 2000. (Ref. 5) V.Tarokh, H. Jafarkhani, and A. R. Calderbank, "Space-Time block codes from orthogonal designs, "• IEEE Trans. Inform. Theory, vol.45, pp.1456-1467, Oct. 1999. Disclosure of the Invention. (Ref. 6) S .M.Alamouti, "A simple transmitter diversity scheme for wireless communications," IEEE J. Select. Areas Commun., vol._^16, pp.1451-1458, Oct. 1998. (Ref. 7) V.Tarokh, H. Jafarkhani, and A. R.Calderbank, "Spacetime block codes for wireless communications: performance results, " IEEE JSAC, vol.17, pp.451-460, Mar. 1999.

Disclosure of Invention

1. Object to be solved by the invention In the above-described decoding method, a symbol is estimated on the assumption that the transfer function of a transmission path can be written as H_{2 j} , „^A ^ H_{23 + x} , _n ^A , H_{2 j} , _n ^B ^ H_{2 i + 1 r n} ^B . However, as specified in Ref.3, when the characteristic of the transmission path has the characteristic of the multi-paths, the above-described approximation is not necessarily established. Accordingly, if the symbol is estimated on the above-described assumption, deterioration in error property of the system is thereby caused. In addition, when the influence of the time selective fading becomes large by following after large temporal variance of the multi-path environment like mobile communication, even if the transfer function of the transmission path can be estimated by Eq. (12) using the preamble, the transfer ■function of the transmission path varies with time. Therefore, the estimate value of the above-described transfer function is greatly deviated from the actual transfer function, thereby deteriorating the error property of the system. Particularly, in the mobile communication where a moving body moves relatively high speed, the problem_^ of deterioration in error property caused by time selective fading is conspicuous . Therefore, an object of the present invention is to provide a communication technology capable of performing accurate demodulation even when the characteristic of the transmission path has the characteristic of the multi-paths and even when the time selective fading is conspicuous.

2. Means for solving the problems First, the principle of the present invention will be explained, and thereafter, the structure and the action of the present invention will be explained.

[1] Principle of the present invention Here, for simplifying the explanation, explanation will be given to a system having two transmitting antennas and one receiving antenna. Note that regarding a case where the number of the antennas is generalized, explanation will be given using embodiments.

(1) Demodulating method of a transmit symbol in each block First, explanation is given to a demodulating method of a transmit symbol in each block capable^, of suppressing the influence of the multi-path fading. In the present invention, first, on the transmitter side, when the STBC-processing is performed, two mutually orthogonal symbol sequences X_n ^A and X_n ^B are generated in each block. For the aforementioned symbol sequences X_n ^A and X_n ^B, for example, Eq. (1), Eq. (2), Eq. (3), and Eq. (4) can be used. Hereafter, explanation is given to Eq. (1) and Eq. (2) where the STBC-processing is performed. Next, OFDM modulation is performed for the generated symbol sequences X_n ^A and X_n ^B, in the same way as described in the section of "Background art", and the symbol sequences are transmitted from two transmitting antennas A and B by a transmitter diversity system. On the receiver side, the signal transmitted from the transmitter is received, by applying sampling and discrete Fourier transform to the signal thus received, and the signal is thereby demodulated. The symbol sequence obtained by demodulation can be written as Eq. (5) and Eq. (6) . Here, in the demodulating method of the present invention, the assumption expressed by, H_2D , _n ^A ^H₂- _{+ i} , _n ^A _> H₂₃ , _n ^B ^H_{23 + 1} , _n ^B is not used. Therefore, when complex conjugate of Eq. (6) is taken, and Eq. (5) and Eq. (6) are rewritten in a matrix form, Eq. (14) is obtained as follows: ^r2_Λn ^■ H^π2^Aj,n ⁿ2₃,n ^x2₃,n LΓA* (14) ^r2 +l,n ^■a2₃ l,n ⁿ2 +l,n 2₃ l,n

From Eq. (14), symbols x_2] , _n, X2_{3 +} ι,_n ^* can be obtained by Eq. (15) , using the calculation equation of second inverse matrix.

■^c2j, ^x2j+l,n

(2) Estimation method for transfer function of transmission path In order to realize a demodulating method of the transmit symbol by Eq. (15) , it is necessary to obtain the transfer functions

H_2D,_n ^A, H_{2:] +} ι,_n ^A of the transmission path related to the 2j-th>and

2j+l-th sub-carriers between the transmitting antenna A and the receiving antenna, and the transfer functions H_2D,_n ^B, H₂-, ₊ ι,_n ^B of the transmission path related to the 2j-th and 2j+l-th sub-carriers between the transmitting antenna B and the receiving antenna, for each block (each time)n. Therefore, the present invention uses an updating method, in which by using the estimate value of the transfer function of Eq. (13), a hard decision value of the symbol of the first block is obtained, and by using the hard decision value of the symbol of the first block thus obtained and the receive symbol, the estimate value is sequentially updated. Specifically, the transfer function is estimated in the following way. First, as a premise for the estimation, the symbol sequence to be transmitted has a preamble first, and subsequently the symbol sequence of transmitting data is transmitted. In addition, the block number of the block transmitted immediately after the preamble is expressed by 0, and the receive signal of the i-th sub-carrier in the block is expressed by ri_Λo hereunder. Also, the block number of the block transmitted n-th after the preamble is expressed by n-1, and the receive signal of the i-th sub-carrier in the block is expressed by r_i/n-ι- First, on the assumption that equation expressed by H_2j,o^A ^H_{2j +} ι , o^A, H_{2 j} , ₀ ^B ^H_{2 j +} ι, o^B , is satisfied, the estimate value of the initial transfer function H_2j , ₀ ^A _f H_{2j r 0} ^B is obtained by Eq. (13) using the preamble, by the method described in the section of "Background art". Next, on the assumption that approximations expressed by H_{2 j} , ₀ ^Ai?H_{2j +} i ₀ ^A, H_2j , o^B^H_{2j + 1}, ₀ ^B are satisfied, the symbol {x_f,₀l of the 0-th block is restored by Eq. (16) , by using the estimate value of the transfer functions H₂₃ , ₀ , H_{2 j} , o ^B _<■ and the receive signal [r_1(n ; i=0,---,M-l} of the 0-th block.

Subsequently, the hard decision value of the symbol {x_x , ₀ } is obtained by Eq. (17) . ^χι_fi = [^χ,,o] (17) Next, here, on the assumption that the 'transfer function has almost no variance (that is, dH/dt^0) among continuous blocks, it is assumed that the estimate value of the transfer function H_2:i/1 ^A, H_23/1 ^B of the first block is the same as the estimate value of the transfer function H_2]/0 ^A, H_23<0 ^B of the 0-th block. Note that the above-described assumption is generally established. Then, in the same way as described above, on the assumption that the approximations expressed by H_2;) , _X ^A ^E_{2l +} ι , ι^A , H₂ - , ^B ^E^-, _{+ i} , ι^B are satisfied, the symbol {x_x , i } of the first block is restored by Eq. (16), using the estimate value of the transfer functions H_2D,_I ^A, H._2?,_I ^B and the receive signal {r_lfl ; i=0, ^•••,M-l} of the first block. Then, in the same way as Eq. (17), the hard decision value of the symbol {x_{x r} i } of the first block is obtained. Next, in Eq. (5) and Eq. (6), if the block numbers 0 and 1 are taken into consideration, each receive signal can be written as Eq. (18) .

The approximations expressed byH _], ₀ ^Ai?H_2;ι , _λ ^A , H₂-, , ₀ ^B ^H₂₃ , ι^B _: H_{2D + I}, o^Ai?H_{2;j +} ι, ι^A, H_{23 +} ι, o^Bi?H_{2ll +} ι, ι^B are obtained by expressing Eq. (18) by a matrix. When considering such a matrix, Eq. (19) is obtained as follows: r TTA T τjTBB** ^r2 ,0 ^r23+l,0 ^X2₃fl ^2 +1,0 ^Λ 3,0 ~^tl2₃+lfi (19) ^r2M ^r23+l,l _ _ ^23,1 ^23+1,1 . _. ^H£ιfl #2j+l,0

Here, if Eq. (20) is established, Eq. (19) can be solved, and by using the hard decision value of the symbols {x , ₀ }, {x_^. , _L } of the 0-th and first block, the estimate value of a new transfer function can be obtained by Eq. (21) .

#2j,2 Hξ,2

The symbol {x_lι2) of the second block is decoded by Eq. (15) , using the estimate value of the transfer function newly obtained. In addition, if the hard decision value of the symbols {x_{x r n} } {xι,_n+ιl of the n-th block and the n+l-th block is obtained by Eq. (15) , the estimate value of the newly transfer function can be obtained by Eq. (22) .

Specifically, the estimate value of the transfer function in each time can be obtained by using the receive signal in a time axis direction n and in a frequency direction j and the hard decision value of the symbol.

(3) Demodulating method of the transmit symbol in each sub-carrier In the mobile communication, particularly the influence of time selective fading becomes large. Therefore, explanation is given to a demodulating method of the transmit symbol in the sub-carrier effective for suppressing the influence of the time selective fading. First, the symbol sequence of transmission data inputted in the transmitter is expressed by X={---, x_{i ;} xi₊ i, ^••■} as described above. Then, the symbol sequence X is divided into blocks comprising M symbols, and made to be parallel for each block, and M sub-carriers are thereby generated. Now, the symbol sequence of the k-th sub-carrier is expressed by X_k= {^■■-, x_k/2q\ Xk,2_{q +} ι. "'} (k=0, 1, ^•■•,M-l) . Here, x_k, _2q is the k-th sub-carrier in the 2q-th block. Next, in the transmitter, space time block coding is applied for the symbol sequence X_k of each sub-carrier, and two mutually orthogonal symbol sequences X^A _k,X^B _k are thereby generated. As the symbol sequences X^A _k,X^B _k, various constituting method can be considered, in the same way as Eq. (1) , Eq. (2) , Eq. (3) , and Eq. (4) - However, here, as one of the examples, explanation is given to a method using the symbol sequences of Eq. (23) and Eq. (24) .

%k — {^{■ • •} , ^xk,2q, ^xk,2q+l, k,2q+2, ^xk,2q+2, - - -} = [^xk,2q, ^xk,2q+l] (23) XS = {^• ,2g+l) ^Xk,2qι ^xh,2q+3ι ~^xk,2q+2ι ^' a; k,2q+l> X "kfc,Λ2g. (24)

After OFDM modulation is performed to the sub-carrier comprising the above two symbol sequences X^A ,X^B the sub-carrier thus modulated is transmitted by a transmitter diversity system. In the receiver, the sub-carrier thus transmitted is received by one antenna, and the receive signal is sampled, and by applying DFT and serial parallel conversion thereto, the receive symbol sequence of each sub-carrier R_k={---, r_{k 2q}, r_k,_{2q + 1}, ^■■■} is restored. n, _q = Xk, _qtl _2q + x _2q+1 Hξ_2q (25) n,2q+l = £fc,2₃+l#fc,2_g+l - ^Xt,2qH_kj2q+l (26) From the above equations, in the same way as the above-described Eq. (15), the symbols x_k, _2q, x_k/2q+ι^* can be obtained by Eq. (27) .

(4) Estimation method of the transfer function of the transmission path Finally, explanation will be given to the estimation method of the transfer function of the transmission path which performs time development by the system in which the above description (3) is realized. In order to estimate the transfer function of the transmission path by this system, firstly, the symbol sequence

(preamble) as shown in Eq. (28) and Eq. (29) is transmitted from the transmitter to the receiver at the time of n, n+1, and the initial transfer function matrix is thereby obtained. f = o₎P*,ι} (ft = 0,l,.--_I -l) (28) C = o, -c_k,i] {k = 0, 1, • • • , M - 1) (29) However, [c_k ^A,C_k ^B] ^τ is a regular matrix. The preambles C^A,C_k ^B are transmitted by the transmitter diversity system in the same way as the transmit symbol sequence, and received by the receiver. The receive signal of the preamble thus received can be written as Eq. (30) . ^rlβ — ^Cfc,0#fc,0 + ^C&,0#fc,0 (30)

Here, if approximation is made like H^A _k, ₀ =?H^A _k, i , H^B _{kf 0} ^H^B _{k; α} , Eq. (30) becomes like Eq. (31).

(31)

Accordingly, since [c_k ^A ,C_k ^B] ^τ is a regular matrix, the transfer functions H^A _k(0> H^B _k,₀ can be obtained by Eq. (32).

# o Ckfi Ck,0 ¹ k,0 (32) H^B Cfc,l — Ck,l ' k,l

The transfer functions H^A _k,₀» H^B _k/0 thus obtained are used as initial values of the transfer function matrix. The symbol sequences X_k ^A,X_k ^B of transmitting data expressed by Eq. (23) and Eq.

(24) are transmitted after the preambles. By receiving the symbol sequences X_k ^A,X_k ^B thus transmitted, the symbol sequences expressed by Eq. (25) and Eq. (26) can be obtained. Then, the symbols x_k,_0r Xk_{+ 1},0 ^χk , i Xk₊ ι,ι of the 0-th block and the first block can be obtained by Eq. (27) . Subsequently, the hard decision values of the symbols thus obtained are determined, and Eq. (33) is obtained by substituting the hard decision values thus determined for Eq.

(25) and Eq. (26) . (33)

Then, on the assumption that the transfer function of the adjacent sub-carrier is approximately the same value, and if the approximation is made like H^A _k, ₀ ^H^A _k+ι , ₀ , H^A , _x ^H^A _{k +} ι , _x , H^B _k , ₀ ^ H^B _{k +} i,o, H^B _k, x ^H^B _k+ι, i , Eq. (33) can be written as Eq. (34). Here, ^«J indicates the hard decision value.

Accordingly, if the regular matrix related to the symbol x of the left-hand side is formed, new transfer function matrix can be obtained by Eq. (35) .

In the same way, while obtaining the hard decision values and new transfer function matrix of the symbols x_k, _n , x_{k +} ι , _n , the transfer function matrix is updated with time. Thus, even in an environment where the time selective fading is large, the transfer function matrix is updated following after the temporal variance of the fading. Therefore, it becomes possible to suppress the influence of the time selective fading given on the error property of the system.

[2] Structure and action of the present invention ⁵ A first structure of the present invention provides a communication method for conducting wireless communication of a transmit symbol sequence between a transmitter and a receiver by conducting wireless communication from n_τ (n_τ≥2) transmitting antennas by a transmitter diversity system after dividing a transmit symbol sequence into blocks comprising a prescribed number of symbols, and encoding them by space-time block coding (referred to as "STBC" hereafter) or space-frequency block coding (referred to as "SFBC" hereafter) for each block in a transmitter, and demodulating the transmit symbol sequence based on a receive symbol sequence obtained by receiving wireless signals transmitted from each transmitting antenna by n_R (n_R ≥l) receiving antennas, and the communication method for conducting wireless communication of the transmit symbol sequence by repeating decision feedback channel estimation process, comprising: a first step of estimating the transmit symbol sequence by decoding STBC-processed codes or decoding SFBC-processed codes by hard decision, based on the value of each transfer function previously stored in a transmitting function storage part and each of the receive symbol; a second step of estimating the value of the transfer function of each channel by dividing a vector whose element is a receive symbol per unit block (referred to as "transmit symbol vector") , by a vector whose element is a transmit symbol sequence per unit block estimated by the first step (referred to as "receive symbol vector") ; and a third step of updating the value of the transfer function stored in a transfer function storage part to the va^lue of the transfer function estimated by the second step, when the second step estimates the value of the transfer function. According to the above-described structure, in the first step of the decision feedback channel estimation process, by decoding the STBC-processed code by hard decision, the transmit symbol sequence is restored from the receive symbol sequence. Here, it is previously found that discrete values are employed in each transmit symbol. Therefore, by using the hard decision, decoding error of the transmit symbol caused by the varying transfer function generated by the influence of the varying fading environment is removed. In the second step, by dividing the transmit symbol vector from which the error is removed, by the receive symbol vector, the transfer function of each channel that varies by the influence of fading, etc., can be reversely estimated. Specifically, on the assumption that the transmit symbol sequence restored in the first step is at least the same symbol sequence as the transmit symbol sequence already transmitted, the receive symbol vector is assumed to be the response to the channel for the input of the transmit symbol vector thus transmitted. Then, the transfer function of each channel can be obtained as a matrix obtained by dividing the transmit symbol vector by the receive symbol vector. Subsequently, in the third step, by updating the transfer function of the transfer function storage means to the transfer function estimated by the second step, the transfer function used for restoring the receive symbol of the next block can be updated to the transfer function newly measured. ⁵ In the above-described way, by using the transmit symbol obtained by hard decision, and subsequently updating the transfer function, it becomes possible to demodulate the transmit symbol by using the transfer function adaptively following each fading environment, even in the frequency selective fading environment or the time selective fading environment. Therefore, it becomes possible to suppress the influence of the frequency selective fading environment and the time selective fading environment given on the error property of the communication. A second structure of the communication method of the present invention according to the first structure comprises: in a transmitter, dividing a transmit symbol sequence for transmitting from the transmitter to a receiver, into data flames comprising a prescribed number of blocks; alternately transmitting a preamble comprising a symbol sequence of known pattern (referred to as "training sequence" hereafter) and the data flame as a transmit symbol sequence; in a receiver, when the preamble is received, estimating the value of the transfer function of each channel by dividing a vector whose element is a receive symbol of the preamble, by a vector whose element is a training sequence of a known pattern; storing the value of the transfer function in the transfer function storage part; and conducting wireless communication of the transmit symbol sequence by repeating the decision feedback channel estimation process, when the data flame is received. As described above, when^" the transfer function is estimated in the second step, the transfer function was obtained on the assumption that the transmit symbol sequence obtained by hard decision is at least the same as the transmit sequence already transmitted. However, the above assumption is not established, when error is generated in hard decision caused by an extremely large influence of fading and noise of the transmission path. Therefore, the transfer function estimated in the second step also becomes erroneous value. Accordingly, in some cases, all the transfer functions that follow include error, thereby gradually deviating from the transfer function of the transmission path. However, according to the above-described second structure, the influence of the error generation in hard decision is cut off, by renewing the transfer function of the transfer function storage part by the transfer function not affected by the error in hard decision, thereby forcibly setting back the transfer function used for decoding the STBC-processed code that follows, to the transfer function adapted to the channel. Thus, propagation of the error can be suppressed. A third structure of the present invention provides the communication method according to ei'ther of the first or second structures, comprising: in the transmitter, generating an OFDM symbol by modulating an STBC-processed symbol sequence by an orthogonal frequency division multiplex (referred to as "OFDM" hereafter) system; ⁵ thereafter, conducting wireless communication from n_τ (n_τ≥2) transmitting antennas by a transmitter diversity system; and in the receiver, generating a receive symbol sequence for wireless signals transmitted from each transmitting antenna, by conducting demodulation of OFDM for the received OFDM symbol sequence received by n_R (n_R≥l) receiving antennas; and based on the receive symbol sequence, demodulating the transmit symbol sequence. With the above-described structure, frequency space can be efficiently used by using OFDM, thereby improving transmission rate. In addition, the influence of the frequency fading can be suppressed. Further, the S/N ratio can be improved by diversity gain by the transmitter/receiver diversity system. A fourth structure of the present invention provides the communication method, comprising: an STBC-processing step of performing STBC-processing for generating two mutually orthogonal symbol sequences X_n ^A and X_n ^B comprising M sub^carriers by dividing a transmit symbol sequence X into blocks comprising M (M≥2) sub-carriers, and based on the symbol sequence X_n (n=0, 1, 2,.... , n is a block number) of each block thus divided; a transmitting step of transmitting each of the symbol sequences X_n ^A and X_n ^B for modulating each of the symbol sequences

X_n ^A and X_n ^B by an OFDM system and transmitting the symbol sequences thus demodulated from two spatially different transmitting positions by a transmitter diversity system; ^ an OFDM demodulating step of demodulating OFDM for demodulating a receive signal by applying discrete Fourier transform thereto obtained by receiving signals transmitted by the transmitting step at one receiving position, thereby generating a receive symbol sequence R_n comprising M sub-carriers; and an STBC demodulating step of demodulating STBC-processed codes for demodulating a symbol sequence X_n' of each block by using the receive symbol sequence R_n for inverse matrix H^_1 of transfer function matrix H, which is constituted based on the transfer function estimated for each block and for each sub-carrier by a prescribed estimation method, and by which the receive symbol sequence R_n is related to the symbol sequence X_n. According to the above-described structure, in the STBC demodulating step, the symbol sequence X_n' of each block is demodulated by using the transfer function matrix H which is constituted based on the transfer function estimated for each block and for each sub-carrier. Therefore, it is not necessary to use the assumption that the frequency dependency of the transfer function is small, or the assumption that the temporal variance of the transfer function is small. Accordingly, it becomes possible to demodulate the symbol sequence X_n' by using the transfer function matrix H adapted to each fading environment, even in the frequency selective fading environment or the time selective fading environment. Thus, it becomes possible to suppress the influence of the frequency selective fading environment and the time selective fading environment given on the error property of the communication. Here, "block" refers to a subset of the sub-carriers simultaneously transmitted in one transmit period of symbols by the OFDM system. The "sub-carrier" refers to wave propagation in each stage for making a demodulated signal used for the final demodulation, or refers to the symbol demodulated by the wave propagation, when multi-stage modulation is performed. As the "two mutually orthogonal symbol sequences X_n ^A, X_n ^B comprising M sub-carriers", for example, the symbol sequences expressed by Eq. (1) and Eq. (2) , and the symbol sequences expressed by Eq. (3) and Eq. (4) are used. Note that the symbol sequences Xi X_n ^B are "orthogonal" to each other means that the equation expressed by X_n ^{A •} X_n ^B * = 0 is established. "a prescribed estimation method" does not particularly limit the estimation method of the transfer function, and for example, it is possible to use the estimation method explained in the section of "(2) Estimation method of time-developed transfer function of the transmission path" in the above-described " [1] Principle of the present invention". "Transmit functional matrix H by which the receive symbol sequence R_n is related to the symbol sequence X_n" refers to the matrix whose element is each transfer function, by which each symbol included in the symbol sequence X_n or the symbol being in complex conjugate relationship with each symbol, or the symbol obtained by multiplying the above symbols by a constant, is related to each symbol included in the receive symbol sequence R_n thorough primary transformation. The matrix on the right-hand-side of Eq. (14) can be given as an example. A fifth structure of the present invention provides the communication method according to the fourth structure, comprising: a preamble transmitting step of transmitting preambles for transmitting symbol sequences from two spatially different transmitting positions by a transmitter diversity system, by modulating each of the preambles C_n ^A and C_n ^B by an OFDM system, using two symbol sequences C_n ^A and C_n ^B comprising M sub-carriers that form a regular matrix [c_n ^A , C_n ^B ] ^τ as preambles; an initial transfer function estimating step of estimating an initial transfer function H by demodulating a receive signal obtained by receiving signals transmitted by the preamble transmitting step at one receiving position by applying discrete Fourier transform thereto, thereby generating a receive symbol sequence R^c _n comprising M sub-carriers, and using the receive symbol sequence R^c _n for an inverse matrix of a matrix (C_n ^A , C_n ^B ) ^τ constituted of the known symbol sequences C_nA and C_nB, thereby obtaining the transfer function; and a hard decision step of performing hard decision for obtaining hard decision values X_n, " , X_n+ι" of the symbol sequences X_n' i Xn₊i' from the symbol sequences X_{n r} Xn+i' demodulated by the STBC demodulating step by using the transfer function matrix H, based on receive symbol sequences R_n, R_n+ι generated by demodulating the receive signal obtained by receiving the transmission signal of the symbol sequences X_n, X_n+ι of two blocks, to which space time block coding is applied, and which is subsequently transmitted by the OFDM demodulating step; and a transfer function updating step of updating the transfer function for estimating a new transfer function matrix H from hard decision values X_n", X_n+ι" of symbol sequences X_n' , X_n+ι' and 'the receive symbol sequences R_n, R_n+ι- According to the above-described structure, the transfer function in transmitting the foremost two blocks of the symbol sequence X_n is estimated in the initial transfer function estimating step. Then, thereafter, by alternately repeating the hard decision step and the transfer function updating step, the hard decision value of the block of the symbol sequence X_n is obtained from the estimate value of the transfer function and the receive symbol sequence, and the estimate value of the transfer function is updated from the hard decision value of the block thus obtained and the receive symbol sequence, and such an operation is repeated. Thus, it becomes possible to demodulate the symbol sequence X_n' while varying the estimate value of the transfer function adaptively to the momentarily varying fading environment. A sixth structure of the present invention provides a communication method, comprising: an STBC processing step of performing STBC-processing for generating a symbol sequence X_k (k=0, ..., M-l) of sub-carriers of M-columns by dividing a transmit symbol sequence X into blocks comprising M (M>2) sub-carriers so as to be made parallel per block unit, and generating two mutually orthogonal symbol sequences X_kA, X_kB, based on the symbol sequence X_k of each sub-carrier; a transmitting step of transmitting symbol sequences from two spatially different transmitting positions by a transmitter diversity system, by demodulating a combination of the symbol sequences {XA} and {X_kB} for each block by an OFDM system; an OFDM demodulating step of demodulating OFDM-processed codes for generating a receive symbol sequence R_k (k=0, ..., M-l) of the sub-carriers of M-columns, by applying discrete Fourier transform to a receive signal obtained by receiving signals transmitted by the transmitting step at one receiving position; and an STBC demodulating step of demodulating STBC-processed codes for demodulating a symbol sequence X_k' of each sub-carrier by using the receive symbol sequence R_k for inverse matrix H^"1 of transfer function matrix H, which is constituted based on a transfer function estimated for each block and for each sub-carrier by a prescribed estimation method, and by which the receive symbol sequence R is related to the symbol sequence X_k. According to the above-described structure, in the STBC demodulating step, by using the transfer function matrix H which is constituted based on the transfer function estimated for each block and for each sub-carrier, the symbol sequence X' of each sub-carrier is demodulated. Therefore, it is not necessary to assume that the frequency dependency of the transfer function is small and the temporal variance of the transfer function is small. Accordingly, it becomes possible to demodulate the symbol sequence X' by using the transfer function matrix H adapted to each fading environment in the frequency selective fading environment or the time selective fading environment. Therefore, it becomes possible to suppress the influence of the frequency selective fading environment and the time selective fading environment given on the error property of the communication. Here, as the "two mutually orthogonal symbol sequences X_k ^A, X^B", for example, the symbol sequences expressed by Eq. (23) nd Eq. (24) are used. "Prescribed estimation method" does not particularly limit the estimation method of the transfer function, and for example, it is possible to use the estimation method explained in the section of "(4) Estimation method of time-developed transfer function of the transmission path" in the above-described " [1] Principle of the present invention". "Transmit functional matrix H by which the receive symbol sequence R_κ is related to the symbol sequence X_κ" refers to the matrix whose element is each transfer function by which each symbol included in the symbol sequence X_k or the symbol being in complex conjugate relationship with each symbol, or the symbol obtained by multiplying the above symbols by a constant, is related to each symbol included in the receive symbol sequence R_k thorough primary transformation. The inverse matrix of the matrix on the right-hand-side of Eq. (27) can be given as an example. A seventh structure of the present invention according to the sixth structure provides a communication method, comprising: a preamble transmitting step of ^'transmitting preambles for transmitting preambles by a transmitter diversity system from two spatially different transmitting positions by modulating each combination of preambles {C_k ^A}, {C_k ^B} for each block by an OFDM system, using the symbol sequences C_k ^A, C_k ^B (k=0,'l,.... M-l) of the sub-carriers of M-columns that form a regular matrix of [c_k ^A , C_k ^B ] ^τ as preambles; an initial transfer function estimating step of estimating an initial transfer function matrix for estimating an initial transfer function matrix H by demodulating the receive signal obtained by receiving the signal transmitted by the transmitting step at one receiving position, by applying discrete Fourier transform thereto, to generate the receive Symbol sequence R^c _k of the sub-carriers of M-columns, and using the receive symbol sequence R^c _k for the inverse matrix of the matrix (C_k ^A , C_k ^B )^τ constituted of the known symbol sequences CA and C_kB, thereby obtaining the transfer function; a hard decision step of performing hard decision for obtaining hard decision values "X_k, X_k+ι" of the symbol sequences X ' , X_k+ι' from the symbol sequences X_k' , X_k+ι' demodulated by using the transfer function matrix H in the STBC demodulating step, based on the receive symbol sequences R_k, R_+i generated by demodulating the receive signal obtained by receiving the transmission signal of the symbol sequences X_k, X_k+χ of the sub-carriers of two-columns, to which space time block coding is applied, and which is subsequently transmitted in the OFDM demodulation step; and a transfer function updating step updating the transfer function for estimating a new transfer function matrix H from hard decision values X", X_k+ι" and receive symbol sequences R_k, R₊χ. According to the above-described structure, the transfer function in transmitting the foremost two blocks of the symbol sequence X_n is estimated in the initial transfer function estimating step. Then, thereafter, by alternately repeating the hard decision step and the transfer function updating step, the hard decision value of the block of the symbol sequence X_n is obtained from the estimate value of the transfer function and the receive symbol sequence, and the estimate value of the transfer function is updated from the hard decision value of the block thus obtained and the receive symbol sequence, and such an operation is repeated. Thus, it becomes possible to demodulate the symbol sequence X_k' while varying the estimate value of the transfer function adaptively to the momentarily varying fading environment . A first structure of a communication system of the present invention comprises: a transmitter comprising an BC encoder for dividing an inputted transmit symbol sequence into blocks comprising a prescribed number of symbols, and encoding the symbol sequence thus divided by a space-time block coding (referred to as "STBC" hereafter) or space frequency block coding (referred to as "SFBC" hereafter) for each block; a diversity transmitter for conducting wireless transmission of STBC-processed codes or SFBC-processed codes of n_τ sequences outputted by a BC encoder from n (n_τ≥2) transmitting antennas by a transmitter diversity system; and a receiver for demodulating the transmit symbol sequence, based on a receive symbol^' sequence obtained by receiving wireless signals transmitted from each transmitting antenna by n_R (n_R≥l) receiving antennas, the receiver further comprising: a transfer function storage part for storing the value of the transfer function of a channel between each transmitting antenna and each receiving antenna; the BC decoder for estimating the transmit symbol sequence by decoding STBC-processed codes or decoding SFBC-processed codes by hard decision, based on the value of each transfer function stored in the transfer function storage part and a receive symbol; a transfer function computer for estimating the value of the transfer function of each channel, by dividing a vector (receive symbol vector) whose element is the receive symbol per unit block, by a vector (transmit symbol vector) whose element is the transmit symbol sequence per unit block estimated by the BC encoder; and a transfer function updating part for updating the value of the transfer function stored in the transfer function storage part, to the value of the transfer function estimated by the transfer function computer, every time that the value of the transfer function is estimated by the transfer function computer. According to the above-described structure, on the side of the transmitter for transmitting the transmit symbol sequence, the BC encoder encodes the transmit symbol sequence into STBC-processed codes or SFBC-processed codes per block unit, and transmits the transmit symbol sequence thus encoded from n_τ antennas by a transmitter diversity system. On the side of the receiver, decoding of the STBC-processed codes or SFBC-prodessed codes by hard decision is performed by using the transfer function stored in the transfer function storage part, for the receive symbol sequence received by n_R receiving antennas, and the transmit symbol sequence is estimated and outputted. Thus, by using hard decision, even when the transfer function varies a little bit by temporal fluctuation of the fading environment, the error caused by the transfer function is removed, and original transmit symbol sequence is restored. Meanwhile, the transfer function computer divides the receive symbol vector by the transmit symbol vector from which the error is removed by hard decision by the BC decoder. Thus, the value of the transfer function of each channel fluctuated by the variance of the fading environment can be estimated. The transfer function updating part stores the newly obtained transfer function in the transfer function storage part and updates the same. Thus, it is possible to decode BC by using the transfer function newly obtained when decoding the block received at the next time. Accordingly, the transfer function is subsequently updated by following after and adapting to the fluctuation of the fading environment. Therefore, it becomes possible to suppress to minimum the influence of the frequency selective fading and the time selective fading given on the error property of the communication system. Here, when the STBC-processing is used, an STBC encoder is used as a BC encoder, and an STBC decoder is used as a BC decoder. Also, when coding by SFBC, an SFBC encoder is used as a BC encoder, and the SFBC decoder is used as a BC decoder. A second structure of a communication system of the present invention according to the first structure comprises, a transmitter comprising: a flame dividing part for dividing the transmit symbol sequence to be transmitted to the receiver into data flames comprising a prescribed number of blocks; a preamble generator for generating a preamble comprising a symbol sequence of known pattern (referred to as "training sequence" hereafter) ; and a preamble inserting part for inputting the preamble and the data flame in the BC encoder alternatively as the transmit symbol sequence, and a¹ receiver comprising a transfer function estimating part for estimating the value of the transfer function of each channel by dividing a vector whose element is the receive symbol of the preamble, by a vector whose element is a training sequence of known pattern, and storing the value of the transfer function in the transfer function storage part, wherein the transfer function computer and the transfer function updating part estimate the value of the transfer function of each channel, and update the value of the transfer function stored in the transfer function storage part, respectively when the data flame is received. According to the above-described structure, when the data flame is received by the receiver, as described above, the transfer function computer and the transfer function updating part estimate the value of the transfer function of each channel, and update the value of the transfer function stored in the transfer function storage part. Thus, the transfer function is subsequently updated, following after and adapting to the fluctuation of the fading environment, and the influence of each kind of fading given on the error property of the communication system is suppressed to minimum. Meanwhile, when the fading environment varies extremely rapidly, and the transfer function is fluctuated extremely rapidly, or when a large noise is superimposed on the receive symbol, error is generated in the value of hard decision when the hard decision is performed by the BC decoder. In such a case, the influence of the error is also present in the transfer function outputted by 'the transfer function computer. The transfer function affected by the error is used for decoding STBC-processed code or SFBC-processed code of the block received at the next time, and therefore the influence of the error is propagated. Therefore, the preambles are inserted between data flames by the preamble inserting part at prescribed intervals. Then, when the preambles are received, the transfer function renewing part estimates the value of the transfer function of each channel, by dividing the vector whose element is the receive symbol, by the vector whose element is the training sequence. Thus, the above-described propagation of the error is cut off, thereby suppressing an error rate from being degraded due to a burst error. A third structure of the communication system of the present invention according to either of the first or second structure comprises : a transmitter comprising an OFDM modulator for modulating STBC-processed codes or SFBC-processed codes of n_τ sequences outputted by the BC encoder by an orthogonal frequency division multiplex (referred to as "OFDM" hereafter) system, thereby generating OFDM symbols, wherein the diversity transmitting part functions to conduct wireless transmission of the OFDM symbol sequence of n_τ-column modulated by the OFDM modulator, from n_τ (n_τ≥2) transmitting antennas by a transmitter diversity system, and a receiver comprising: a receiving part for receiving wireless signals which are transmitted from each transmitting antenna by n_R (n_R≥l) receiving antennas; and an OFDM demodulator for demodulating the receive signal received by the receiving part by the OFDM system, thereby generating the receive symbol sequence. By such a structure, the frequency space can be efficiently used by using the OFDM system, and the transmit rate can be improved. In addition, the influence of the frequency fading can be suppressed.

Further, the S/N ratio can be improved by diversity gain of the transmitter/receiver diversity. A fourth structure of a communication system of the present invention, comprises: an STBC encoder for generating two mutually orthogonal symbol sequences X_n ^A, X_n ^B comprising M sub-carriers by dividing the symbol sequence X to be transmitted into blocks comprising M (M 2) sub-carriers, based on the symbol sequence X_n (n=0, 1, 2, ...; n is a block number) of each block; a transmitting part for modulating each of the symbol sequences X_n ^A, X_n ^B by the OFDM system, arid transmitting the symbol sequence thus demodulated from two spatially different transmitting positions by a transmitter diversity system; an OFDM demodulator for demodulating the receive signal obtained by receiving the signal transmitted by the transmitter at one receiving position, by applying discrete Fourier transform thereto, and generating the receive symbol sequence R_n comprising

M sub-carriers; and an STBC demodulator for demodulating the symbol sequence X_n of each block by using the receive symbol sequence R_n for inverse matrix H"¹ of transfer function matrix H, which is constituted based on the transfer function estimated for each block and for each sub-carrier by a prescribed estimation method, and by which the receive symbol sequence R_n is related to the symbol sequence X_n. According to the above-described structure, the symbol sequence X_n' of each block is demodulated by the STBC demodulator, using the transfer function matrix H which is constituted based on the transfer function estimated for each block and for each sub-carrier. Therefore, as described above, it is not necessary to assume that the frequency dependency of the transfer function is small, or the temporal variance of the transfer function is small. Thus, it becomes possible to demodulate the symbol sequence X_n' by using the transfer function matrix H adapted to each fading environment, even in the frequency selective fading environment or the time selective fading environment. Accordingly, it becomes possible to suppress the influence of the frequency selective fading environment and the time selective fading environment given on the error property of the communication system. A fifth structure of the communication system of the present invention according to the fourth structure, comprises: a preamble transmitting part for demodulating by an OFDM system each of the two symbol sequences C_n ^A, C_n ^B comprising M sub-carriers that form a regular matrix [C_n ^A, C_n ^B3 ^τ by using such two symbol sequences as preambles, and transmitting the symbol sequence thus demodulated from two spatially different transmitting positions by a transmitter diversity system; an initial transfer function estimation part for estimating an initial transfer function matrix H by applying the discrete Fourier transform to a receive signal obtained by receiving the signals transmitted by the preamble transmitting part at one receiving position, demodulating it and generating a receive symbol sequence R^c _n comprising M sub-carriers, and obtaining the transfer function by operating the inverse matrix of the matrix (C_n ^A, C_n ^B)^T constituted of the known symbol sequences C_n ^A , C_n ^B,to the receive symbol sequence R^c _n ; and a hard decision unit for demodulating the receive signal obtained by receiving the transmission signal of symbol sequences Xn, X_n+i of two blocks, to which space time block coding is applied, and which is subsequently transmitted from the transmitter, by the OFDM demodulator, and thereby generating receive symbol sequences Rnr Rn₊i/- and based on the receive symbol sequences R_n, R_n+: obtaining hard decision values "X_n, X_n+ι" of symbol sequences X_n' , X_n+ι' from symbol sequences Xn' , X_n+ι' demodulated by the STBC demodulator using the transfer function matrix H; and a transfer function updating part for estimating a new initial transfer function matrix H, from the hard decision values Xn/' " i Xn+i" and the receive symbol sequences R_n, R_n+ι- According to the above-described structure, the transfer function in transmitting the forefront two blocks of the symbol sequence X_n is estimated by the transfer function renewing part. Then, thereafter, the hard decision unit obtains the hard decision value of the block of the symbol sequence X_n from the estimate value of the transfer function and the receive symbol sequence, and the transfer function updating part updates the estimate value of the transfer function from the hard decision value of the block obtained by the hard decision unit and the receive symbol sequence. Such an operation is alternately repeated. Thus, it becomes possible to demodulate the symbol sequence X_n' while varying the value of the transfer function adaptively to the momentarily varying fading environment . A sixth structure of the communication system of the present invention comprises: an STBC encoder for generating a symbol sequence

X_k (k=0, ..., M-l) of sub-carriers of M-columns by dividing a transmitting symbol sequence X into blocks comprising M (M≥2) sub-carriers, and making them parallel per block unit, and generating two mutually orthogonal symbol sequences X_k ^Aand X_k ^B, based on the symbol sequence X_k of each sub-carrier; a transmitting part for modulating the combination of the symbol sequences {X_k ^A} and {X_k ^B} for each block by an OFDM system and transmitting the symbol sequence thus demodulated from two spatially different transmitting positions by a transmitter diversity system; an OFDM demodulator for demodulating the receive signal obtained by receiving the signal transmitted by the transmitter at one receiving position by applying discrete Fourier transform thereto, and generating a receive symbol sequence R_k (k=0, ..., M-l) of sub-carriers of M-columns; and an STBC demodulator for demodulating a symbol sequence X_k' of each sub-carrier by operating the inverse matrix H^-1 of transfer function matrix H, which is constituted based on a transfer function estimated for each block and for each sub-carrier by a prescribed estimation method and by which the receive symbol sequence R_k is related to the symbol sequence X_k.,to the receive symbol sequence

Rk- According to the above-described structure, the symbol sequence X_k' is demodulated by using the transmission functional matrix H which is constituted based on the transfer function estimated for each block and for each sub-carrier, by the STBC demodulator. Therefore, as described above, it is not necessary to assume that the frequency dependency of the transfer function is small or the temporal variance of the transfer function is small. Thus, it becomes possible to demodulate the symbol sequence X_k' by using the transfer function matrix H adapted to each fading environment, even in the frequency selective fading environment or the time temporal fading environment. Accordingly, it becomes possible to suppress the influence of the frequency selective fading environment and the time selective fading environment given on the error property of the communication system. A seventh structure of the communication system according to the fourth structure comprises: a preamble transmitting part for modulating each combination of the preambles {C_k ^A} and {C_k ^B} for each block, using the symbol sequences C_k ^A, C_k ^B (k=0,l,..., M-l) of the sub-carriers of M-columns that form a regular matrix [C^A , C^B ] ^τas preambles by an OFDM system, and transmitting the symbol sequences thus modulated from two spatially different transmitting positions by a transmitter diversity system; ' a transfer function estimating part for estimating an initial transfer function matrix H, by applying discrete Fourier transform to the receive signal obtained by receiving the signal transmitted by the transmitting part at one receiving position, thereby demodulating the signal thus received, and generating the receive symbol sequence R^c _k of the sub-carriers of M-columns, and operating the inverse matrix of the matrix [C_k ^A , C_k ^B ] ^τ constituted of the known symbol sequences C_kA and C_kB,to the receive symbol sequence R^c _k , , thereby obtaining the transfer function; and a hard decision unit for demodulating the receive signal obtained by receiving the transmission signal of the symbol sequences X_k, X_k+1 of sub-carriers of two-columns to which space time block coding is applied, and which is subsequently transmitted from the transmitter, by the OFDM demodulator, and thereby generating receive symbol sequences R_k, R_k+ι, and based on the receive symbol sequences R_k, R₊ι, obtaining hard decision values X_k, " , X_k+ι" of the symbol sequences X_k' , X_k+ι' from the symbol sequences X_k' , X₊ι' demodulated by using the transfer function matrix H by the STBC demodulating part; and a transfer function updating part for estimating a new transfer function matrix H from the hard decision values X_k", X_k+ι" and the receive symbol sequences R, 'R_k+ι- According to the above-described structure, the transfer function in transmitting the forefront two blocks of the symbol sequence X is estimated by the transfer function renewing. part . Then, the hard decision unit obtains the hard decision value of the block of the symbol sequence X_k from the estimate value of 'the transfer function and the receive symbol sequence, and the transfer function updating part updates the estimate value of the transfer function from the hard decision value of the block obtained by the hard decision unit and the receive symbol sequence. Such an operation is repeated. Thus, it becomes possible to demodulate the symbol sequence X_k' while varying the value of the transfer function adaptively to the momentarily varying fading environment . A first structure of a receiver according to the present invention provides the receiver for demodulating the transmit symbol sequence based on a receive symbol sequence obtained by receiving a wireless signal by n_R (n_R≥l) receiving antennas, the wireless signal being transmitted by a transmitter diversity system from n_τ (n_τ≥2) transmitting antennas after the transmit symbol sequence divided into blocks comprising a prescribed number of symbols is encoded by a space-time block coding (referred to as "STBC" hereafter) or space frequency block coding (referred to as "SFBC" hereafter) for each block, the receiver comprising: a transfer function storage part for storing the value of the transfer function of a channel between each transmitting antenna and each receiving antenna; a BC decoder for estimating a transmit symbol sequence by decoding STBC-processed codes or SFBC-processed codes by hard decision, based on the value of each transfer function stored in the transfer function storage part and each of the receive symbols; a transfer function computer for estimating the value of the transfer function of each channel, by dividing a vector whose element is a receive symbol per unit block, by a vector whose element' is a transmit symbol sequence per unit block estimated by the BCdecoder; and a transfer function updating part for updating the value of the transfer function stored in the transfer function storage part to the value of the transfer function estimated by the transfer function computer every time that the value of the transfer function is estimated by the transfer function computer. Thus, it is possible to obtain the receiver suitable for using in the communication system of the first structure of the present invention. A second structure of the receiver of the present invention according to the first structure comprises: a receiving part for receiving the wireless signal transmitted from each transmitting antenna by n_R (n_R≥l) receiving antennas, wherein the receive symbol sequence is modulated by an OFDM system; and an OFDM demodulator for generating the receive symbol sequence by demodulating the receive signal received by the reception part by the OFDM system. Thus, it is possible to obtain the receiver suitable for using in the communication system of the third structure of the present invention. A third structure of a receiver of the present invention provides the receiver for receiving a signal transmitted from a transmitter, comprising: the transmitter comprising: an STBC encoder for dividing the transmitting symbol sequence X into blocks comprising M (M≥2) sub-carriers, and generating two mutually orthogonal symbol sequences X_n ^A and X_n ^B comprising M sub-carriers based on a symbol sequence X_n (n=0, 1, 2, ...; n is a block number) of each block; and a transmitting part for modulating each of the symbol sequences X_n ^A and X_n ^B by an OFDM system, and transmitting the symbol sequence thus modulated from two spatially different transmitting positions by a transmitter diversity system, and wherein the receiver for receiving the signal transmitted from the transmitter thus constructed and demodulating the symbol sequence X thus transmitted, comprising: an OFDM demodulator for generating a receive symbol sequence

R_n comprising M sub-carriers by applying discrete Fourier transform to a receive signal obtained by receiving signals transmitted by the transmitting part at one receiving position, thereby demodulating receive signals; and an STBC demodulator for demodulating a symbol sequence

X_n' of each block by operating the inverse matrix H^_1 of transfer function matrix H, which is constituted based on the transfer function estimated for each block and for each sub-carrier by a prescribed estimation method, and by which the receive symbol sequence R_n is related to the symbol sequence X_n, to the receive symbol sequence R_n . X_n- Thus, it is possible to obtain the receiver suitable for using in the communication system of the fourth structure of the present invention. The fourth structure of the receiver of the present invention according to the third structure comprises: the said transmitter comprising a preamble transmitting part for modulating each combination of preambles {C_n ^A}, {C_n ^B} by an OFDM system, using two symbol sequences C_n ^A, C_n ^B comprising M sub-carriers that form a regular matrix of [C_n ^A , C_n ^B ] ^τas preambles, and transmitting the preambles thus modulated from two spatially different transmitting positions by a transmitter diversity system and wherein the receiver comprising: a transfer function estimating part for estimating an initial transfer function matrix H, by applying discrete Fourier transform to the receive signal obtained by receiving the signal transmitted by the preamble transmitting part at one receiving position, thereby demodulating the signal thus received, and generating the receive symbol sequence R^c _n comprising M sub-carriers, and operating the inverse matrix of the matrix (C_n ^A , Cn_n ^B )^τ constituted of the known symbol sequences C_nA and C_nB, to the reieive symbol sequence R^c _n , thereby obtaining the transfer function; a hard decision unit for demodulating the receive signal obtained by receiving the transmission signal of symbol sequences X_n, Xn₊i of two blocks, to which -space time block coding is applied, and which is subsequently transmitted from the transmitter, by the OFDM demodulator, thereby generating receive symbol sequences R_n, R_n+ι, and based on the receive symbol sequences R_n, R_n+ι, obtaining hard decision values "X_n, X_n+ι" of the symbol sequences X_n' , X_n+ι' from symbol sequences X_n' , X_n+ι' demodulated by the STBC demodulator using the transfer function matrix H; and transfer function updating part for estimating a new transfer function matrix H from hard decision values X_n", Xn₊i" and receive symbol sequences R_n, R_n+ι- Thus, it is possible to obtain the receiver suitable for using in the communication system of the fifth structure of the present invention. A fifth structure of a receiver of the present invention comprising: a transmitter comprising: an STBC encoder for generating a symbol sequence X (k=0, ..., M-l) of the sub-carriers of M-columns by dividing a transmitting symbol sequence X into blocks comprising M (M≥2) sub-carriers so as to be made parallel per block unit, and generating two mutually orthogonal symbol sequences X_k ^A and X_k ^B, based on a symbol sequence X_k of each sub-carrier; and a transmitting part for demodulating combination of symbol sequences {X_k ^A} and {X^B} for each block by an OFDM system and transmitting the symbol sequence thus demodulated from two spatially different transmitting positions by a transmitter diversity system, and wherein the receiver for receiving the signal transmitted by the transmitter thus constructed and demodulating the symbol sequence X thus transmitted, comprising: an OFDM demodulator for demodulating receive signals obtained by receiving signals transmitted by the transmitter at one receiving position by applying discrete Fourier transform thereto, 'and generating a receive symbol sequence R_k (k=0, ..., M-l) of sub-carriers of M-columns; and an STBC demodulator for demodulating the symbol sequence X_k of each sub-carrier by operating an inverse matrix H^_1 of transfer function a matrix H, constituted based on a transfer function estimated for each block and for each sub-carrier by a prescribed estimation method, by which a receive symbol sequence R_k is related to the symbol sequence X,to the receive symbol sequence R_k. Thus, it is possible to obtain the receiver suitable for using in the communication system of the sixth structure of the present invention. A sixth structure of the receiver of the present invention according to the fifth structure comprises: the said transmitter comprising a preamble transmitting part for modulating each combination of preambles {C_k ^A}, {C_k ^B} for each block by an OFDM system, using the symbol sequences C_k ^A, C_k ^B (k=0, ..., M-l) comprising sub-carriers of M-columns that form a regular matrix of [c_k ^A , C_k ^B ] ^τ as preambles, and _^transmitting the preambles thus modulated from two spatially different transmitting positions by a transmitter diversity system, and wherein the receiver comprising: a transfer function estimating part for estimating an initial transfer function matrix H, by applying discrete Fourier transform to the receive signal obtained by receiving signals transmitted by the preamble transmitting part at one receiving position, thereby demodulating the signals thus received, and generating a receive symbol sequence R^c _n comprising M sub-carriers, and operating the inverse matrix of the matrix (C_n ^A , Cn_n ^B )^τ constituted of the known symbol sequences C_n ^A and C_n ^B,to receive symbol sequence R^c _n , thereby obtaining the transfer function; a hard decision unit for demodulating the receive signal obtained by receiving transmission signals of the symbol sequences X_k X_k+i of sub-carriers of two-columns to which space time block coding is applied, and which is subsequently transmitted from the transmitting part, by the OFDM demodulator, and thereby generating receive symbol sequences R, R₊ι, and based on the receive symbol sequences R_k, R_k+ι, obtaining hard decision values "X , X_k+ι" of the symbol sequences X_k' , X_k+ι' from the symbol sequences X_k' , X_k+ι' demodulated by the STBC demodulator using a transfer function matrix H; and a transfer function updating part for estimating a new transfer function matrix H from the hard decision values X_k", X_k+ι" and the receive symbol sequences R_k, R_k+ι. Thus, it is possible to obtain the receiver suitable for using in the communication system of the seventh structure of the present invention.

Brief Description of Drawings

Fig.l is a block diagram illustrating a basic structure of a communication system according to a first embodiment of the present invention. Fig.2 is a block diagram illustrating the basic structure of the communication system according to the second embodiment of t.he present invention. Fig.3 is a block diagram-illustrating a communication system according to a third embodiment of the present invention. Fig, 4 is a block diagram illustrating the structure of a decision feedback channel estimator (DFCE) 53 of Fig.3. Fig.5 is a schematic view illustrating an example of a full rate STBC encoder 44' , which is an example of an STBC encoder of Fig.3. Fig.6 is a schematic view of an example of a half rate STBC encoder 44", which is an example of the STBC encoder 44 of Fig.3. Fig.7 is a view illustrating^' a channel model in the communication system of Fig.3. Fig.8 is a view illustrating the structure of the communication system according to a fourth embodiment of the present invention. Fig.9 is a block diagram illustrating the structure of the decision feedback channel estimator (DFCE) 53' of Fig.8. Fig.10 is a schematic view illustrating an example of the SFBC encoder 70 of Fig.8. Fig.11 is a block diagram illustrating the structure of a. transmitter by the conventional OFDM-STBC system. Fig.12 is a view illustrating the type of an OFDM signal transmitted from the transmitter. Fig.13 is a block diagram illustrating the structure of a receiver by the conventional OFDM-STBC system.

Best Mode for Carrying out the Invention '

The preferred embodiments of the present invention will be explained with reference to the drawings hereunder.

(Embodiment 1) Fig.l is a block diagram illustrating a basic structure of a communication system according to an embodiment 1 of the present invention. Fig.1(a) illustrates a transmitter, and Fig.1(b) illustrates a receiver. The transmitter 1 comprises an STBC encoder 2, a preamble generator 3, multiplexers 4a and 4b, S/P converters 5a and 5b, IDFTs 6a and 6b, P/S converters 7a and 7b, and transmitting antennas 8a and 8b. A symbol sequence X of transmitting data is inputted in the STBC encoder 2. The STBC encoder divides the symbol sequence X thus inputted into blocks comprising M (M≥2) sub-carriers. Then, based on the symbol sequence Xn (n=0, 1, 2, ...; n is a block number) of each block, two mutually orthogonal symbol sequences X_n ^A and X_n ^B comprising M sub-carriers are generated and outputted. The preamble generator 3 generates and outputs a preamble comprising two symbol sequences C_n ^A and C_n ^B . The symbol sequence C_n — C o , n J C i,_n> '"J ^C M-l,n/> C_n — IC o,n> C ι,_n> ^'"> ^c M - 1 , n J °f the preamble generated by the preamble generator 3 comprises M sub-carriers and satisfies a regular condition such as Eq. (36) . _rA 3,n 2j+l,n ≠ O CJ = 0, 1, " - . /2 - 1) (36) r ^c2^Bj,n r ^C2^Bi+l,n

The multiplexer 4a selects either of the two symbol sequences X_n ^A or C_n ^A inputted, and outputs the symbol sequence selected to the

S/P converter 5a. In addition, the multiplexer 4b selects either of the two symbol sequences X_n ^B or C_n ^B inputted, and outputs the symbol sequence selected to the S/P converter 5b. The S/P converters 5a and 5b make the symbol sequence thus inputted parallel for each block, and outputs it to the IDFTs 6a and 6b as a symbol sequence of sub-carriers of M-columns. The IDFTs 6a and 6b applies inverse discrete Fourier transform to the symbol sequence of the sub-carriers thus inputted for each block, thereby generating an OFDM modulation signal of M-columns, and outputs it to the P/S converters 7a and 7b. The P/S converters 7a and 7b serialize the OFDM demodulation signal of M-columns, and transmit it from the transmitting antennas 8a and 8b. Note that the transmitting antennas 8a and 8b are arranged separately so as to obtain a sufficient transmitter diversity effect. Meanwhile, the receiver 10 comprises a receiving antenna 11, a S/P converter 12, a DFT 13, a P/S converter 14, a transfer function estimating unit (channel estimator) 15, and a STBC decoder 16. The transmission signals transmitted from the transmitting antennas 8a and 8b of the transmitter 1 pass through different paths, respectively, to be inputted in the receiving antennas 11. The S/P converter 12 samples the receive signal inputted in the receiving antenna 11 and makes the symbol sequences parallel to generate sub-carriers of M-columns. The DFT 13 demodulates the symbol sequence of sub-carriers inputted by applying discrete Fourier transform thereto, and generates the symbol sequence comprising sub-carriers of M-columhs. The P/S converter 14 serializes the symbol sequence of M-columns outputted by the DFT 13 for every time, and outputs the receive symbol sequence Rn comprising M sub-carriers for every time. The transfer function estimating unit 15 computes and outputs the estimate value of the transfer function H^A _k, _n, of the path from the transmitting antenna 8a to the receiving antenna 11 for every time and for every frequency, based on the receive symbol outputted from the P/S converter 14, and the estimate value of the transfer function H^B _k _ _n of the path from the transmitting antenna 8b to the receiving antenna 11 for every time and for every frequency. The STBC decoder 16 demodulates the symbol sequence X_n' of each block, based on the receive symbol sequence R_n outputted from the P/S converter 14 and the estimate value of the transfer function

H^A _k , _n , H^B _{k , n} outputted from the transfer function estimating unit 15. The communication method of the communication system according to the embodiments having the above-described structure will be explained hereunder. ^"* First, the preamble generator 3 of the transmitter 1 outputs the preamble comprising symbol sequences C_n ^A , C_n ^B . Here, as an example case, the preamble expressed by Eq. (9) and Eq. (10) is outputted. The multiplexers 4a and 4b select the symbol sequences C_n ^A , C _n ^B of the preamble during output of the preamble from the preamble generator 3, and output it to the S/P converters 5a and 5b. The S/P converters 5a and 5b make the symbol sequences C_n ^A , C_n ^B of the preamble parallel to generate the M sub-carriers. Then, the IDFTs 6a and 6b applies inverse discrete Fourier transform to the symbol sequences C_n ^A , C_n ^B so as to be parallel, and generates an OFDM demodulation signal. The P/S converters 7a and 7b serializes the OFDM demodulation signal, and output it from the transmitting antennas 8a and 8b. In the receiver 10, when the OFDM modulation signal is received by the receiving antenna 11, it is made to be parallel by the S/P converter 12, to which discrete Fourier transform is applied by the DFT 13, and demodulated. Thereafter, the signal thus demodulated is serialized again by the P/S converter 14, and the receive symbol sequence R^c _n is thereby generated. The receive symbol sequence R^c _n Thus generated is inputted in the transfer function estimating unit 15. The receive symbol sequence R^c _n can be written as Eq. (11) and Eq. (12). The transfer function estimating unit 15 estimates an initial transfer function H^A ₂ j , _{n >} H^B ₂ j _n by performing the computation of Eq. (13) . The input of the preamble is followed by the input of the symbol sequence X of transmitting data in the STBC encoder 2. The STBC encoder 2 divides the symbol sequence X thus inputted into blocks comprising M sub-carriers. Then, based on the symbol sequence X_n of each block, the symbol sequences X_n ^A, X_n ^B expressed by Eq. (1) and Eq. (2) are generated and outputted to the multiplexers 4a and 4b. When the input of the symbol sequences X_n ^A, X_n ^B starts, the multiplexers 4a and 4b select and output the symbol sequences X_n ^A, X_n ^B by switching the selection direction. In addition, the symbol sequences X_n ^A, X_n ^B is subjected to OFDM demodulation by the S/P converters 5a, 5b, the IDFTs 6a, 6b, and the P/S converters 7a, 7b, and transmitted by a transmitter diversity from two transmitting antennas 8a and 8b. In the receiver 10, the transmission signal from the transmitter 1 is received, demodulation is performed by the S/P converter 12, the DFT 13, and the P/S converter 14, and the receive symbol sequence R_n is obtained. The R_n is a symbol sequence expressed by Eq. (5) and Eq. (6) . The STBC decoder 16 demodulates sequence X_n' , X_n+ι' by Eq. (16) , from the estimate values of the transfer function H^A _{2 j} , _{n >} H^B _{2 j , n} previously estimated by the transfer function estimating unit 15. Then, the hard decision values X_n", X_n+ι" of the symbol sequence Xn' , Xn₊i' is obtained by Eq. (17) , and outputted as restored symbol sequences . Meanwhile, the transfer function estimating unit 15 estimates the transfer function matrix by Eq. (22) based on the hard decision values X_n", X_n+1" and receive symbol sequence R_n, and outputs it as the estimate value of a new transfer function matrix. By the similar operations, demodulation of the hard decision value X_n", Xn₊i" of the symbol sequences X_n' , X_n+ι'and updating of the estimate value of the transfer function matrix are repeated hereunder. Thus, the receiver of this embodiment continues to demodulate the hard decision value X_n", X_n+ι" of the symbol sequences X_n' , X_n+ι' , while subsequently updating the estimate value of the transfer function matrix following after the varying fading environment. Therefore, it becomes possible to suppress the error property caused by the time selective fading. (Embodiment 2) Fig.2 is a block diagram illustrating a basic structure of a communication system according to an embodiment 2 of the present invention. Fig.2 (a) illustrates a transmitter, and Fig.2(b) illustrates a receiver. The transmitter 20 comprises a S/P converter 21, an STBC encoder 22, a preamble generator 23, multiplexers 24a and 24b, IDFTs 25a and 25b, a P/S converters 26a and 26b, and transmitting antennas 27a and 27b. The S/P converter 21 divides symbol sequences X={'"> x_2j, x₂j + ι, ^■••} serially inputted from outside into blocks comprising M(M≥2) symbols, and generates the symbol sequence X_k={---, x_k,2_j> Xk,2j ₊ ι_> ^•••} (k=0, 1, ^••-,M-l) of sub-carriers of M-columns by parallel-izing each block. The STBC encoder 22 generates two mutually orthogonal symbol sequences X_k ^A, X_k ^B based on each of the ^"^symbol sequences X_k (k=0,l, ^•••,M-l) of sub-carriers of M-columns inputted from the S/P converter 21. The preamble generator 23 generates and outputs preambles C_k ^A, C_k ^B of 2 sequences added to before the transmitting symbol sequences X_k ^A, X_k ^B. The symbol sequencesC_k ^A = {c^A _k ,₀ , c^A _{k ι X} , ^{■ ■ ■}}, C_k ^B = {c^B _k , _o ) c^B _k ,i' "'} comprises M sub-carriers, and satisfies a regular condition of Eq. (37) . 0,l,.--, /2-l) (37)

The multiplexers 24a and 24b select either of the inputted symbol sequences X^A, X_k ^B or the preambles C^A, C^B and output the symbol sequence selected to the IDFT 25a, 25b. The IDFTs 25a and 25b apply inverse discrete Fourier transform to the inputted M symbol sequences for each block, and output them to the P/S converters 26a and 26b. The P/S converters 26a and 26b serialize M OFDM modulation signals inputted from the IDFTs 25a and 25b, to which the inverse discrete Fourier transform is applied, and transmit them from transmitting antennas 27a and 27b. The transmitting antennas 27a and 27b are separately arranged so as to obtain a sufficient diversity effect. The receiver 30 comprises a receiving antenna 31, a DFT 32, a S/P converter 33, a STBC decoder 34, a transfer function estimation unit (channel estimator) 35, and a P/S converter 36. The DFT 32 samples the receive signal received by the receiving antenna 31, applies discrete Fourier transform thereto, and outputs the receive symbol sequence to the S/P converter 33. The S/P converter 33 makes the inputted receive symbol sequence parallel to form M symbol sequences R (k=0, 1, ...;M-1) . The STBC decoder 34 demodulates the symbol sequence X_k' by using each of the symbol sequence R_k generated by the S/P converter 33 for the inverse matrix H^-1 of the transfer function matrix H constituted based on the M X 2 transfer functions H_k ^A, H_k ^B inputted from the transfer function estimation unit 35. The transfer function estimation unit 35 computes the estimate value of the transfer functions H_k ^A, H^B of M X 2 transmission paths by a prescribed method from the symbol sequence obtained by receiving the preamble and a transmit symbol sequence transmitted from the transmitter 20. The P/S converter 36 outputs the symbol sequence X' by serializing M symbol sequences X_k' demodulated by the STBC decoder 34. In the communication system according to this embodiment thus constructed, the communication method will be explained hereunder. First, the preamble generator 23 of the transmitter 20 outputs the preamble comprising the symbol sequences C_k ^A, C_k ^B. Here, as one of the example cases, the preamble expressed by Eq. (28) and Eq.

(29) is outputted. The multiplexers 24a and 24b select the symbol sequences C_k ^A, C_k ^B of the preamble while the preambles are outputted from the preamble generator 23, and output them to the IDFTs 25a and 25b. The IDFTs 6a and 6b apply inverse discrete Fourier transform to the symbol sequences C_k ^A, C^B thus inputted, and generate OFDM demodulation signals. The P/S converters 26a and 26b serialize the OFDM demodulation signals thus generated, and transmit them from the transmitting antennas 27a and 27b. In the receiver 30, when the transmitted OFDM demodulation signal is received by the receiving antenna 31, the receive symbol sequence R^c _k of sub-carriers of M-columns is generated, by applying discrete Fourier transform by the DFT 32, and thereafter making it parallel by the S/P converter 33. The receive symbol sequence R^c _k thus generated is inputted in the transfer function estimation unit 35. The receive symbol sequence R^c _k can be written as Eq. (30) . The transfer function estimation unit 35 estimates the initial transfer function H^A _k , ₀ > H^B _k , ₀ • In the S/P converter 21 of the transmitter 20, the input of the preamble is followed by the input of the symbol sequence X of transmitting data. The S/P converter 21 divides the symbol sequence X thus inputted into blocks comprising M sub-carriers, transforms it into the symbol sequence X_k of sub-carriers of M columns for each block, and inputs it in the STBC encoder 22. The STBC encoder 22 generates the symbol sequences X_k ^A, X_k ^B expressed by Eq. (23) and Eq. (24), based on the symbol sequence X_k of the inputted sub-carriers and output them to the multiplexers 24a and 24b. When the input of the symbol sequences X_k ^A, X_k ^B starts, the multiplexers 24a, 24b select and output the symbol sequences X_k ^A, X_k ^Bby switching the selection direction. Then, the symbol sequences X_k ^A, X_k ^B are subjected to OFDM demodulation by the IDFTs 25a and 25b, and the P/S converters 26a and 26b, and transmitted by a transmitter diversity system from two transmitting antennas 27a and 27b. In the receiver 30, the transmission signal from the transmitter 20 is received, and by demodulating the signal thus received by the DFT 32 and the S/P converter 12, the receive symbol sequence R_k is obtained. The R_k is a symbol sequence expressed by

Eq. (25) and Eq. (26) . The STBC decoder 34 demodulates the estimate value of the symbol sequenceX_k', X_{k +} ι' by Eq. (27') from the transfer function H^A _k,2q» H^B _{/ 2q +} ι previously estimated by the transfer function estimation unit 35 and the receive symbol sequence R_k. Then, the hard decision values X_k", X_k+ι" of the symbol sequence X_k' , X₊ι' is obtained, and outputted as restored symbol sequences. Meanwhile, the transfer function estimation unit 35 estimates the transfer function matrix by Eq. (35) , based on the hard decision values X_k", X_k+ι" and the receive symbol sequence R_k, and updates it as a new estimate value of the transfer function matrix. Thus, in the receiver according to this embodiment, the hard decision values X_k", X_k+ι" of the symbol sequences X_k' , X_k+ι'are demodulated, while subsequently updating the estimate value of the transfer function matrix by following after the varying fading environment. Therefore, it becomes possible to suppress the deterioration in the error property caused by the time selective fading.

(Embodiment 3) In an embodiment 3, a STBC communication system provided with n_τ transmitting antennas and n_R receiving antennas will be explained.

(1) Structure of the communication system Fig.3 is a view illustrating the communication system according to a third embodiment of the present invention. Fig.3 (a) shows a transmitter 1', and Fig.3(b) shows a receiver 30'. The transmitter l¹ comprises a convolutional encoder 40, an interleaver 41, a mapper 42, a S/P converter 43, and an STBC encoder 44, respectively, and also comprises n_τ IDFTs 45, n_τ P/S converters 46, n_τ guard interval inserters 47, and n_τ transmitting antennas 48, respectively. Meanwhile, the receiver 30' comprises n_R receiving antennas 49, n_R guard interval removers 50, n_R S/P converters 51, n_R DFTs 52, and n_R decision feedback channel estimators (referred to as "DFCE" hereafter) 53, respectively, and also a maximum ratio combiner (referred to as "MRC" hereafter) 54 , a P/S converter 55 , a de-mapper 56 , a de-interleaver 57, and a convolutional decoder 58, respectively. The convolutional encoder 40 encodes transmission data into a convolutional code such as a Vitarbi code. The interleaver 41 interleaves the convolutional code outputted by the convolutional encoder 40. Then, the mapper 42 maps the interleaved code, to generate a transmit symbol sequence (^•■•, i-_1; x , x_i+l, ^•••) . The S/P converter 43 makes the transmit symbol sequence (^•••, x_H, x_t, x₁₊₁, ^•■■) parallel in N_sc columns. The transmit symbol sequence thus made to be parallel is described as (^•■-, Xi-_ι,_k, Xi,_k> Xi₊ι,_k> "') (k=l, 2, ^•••, N_sc) . Where, index i denotes an OFDM symbol number, index k denotes a s b-carrier number, and N_so denotes the number of sub-carrier sequences . The STBC encoder 44 applies STBC-coding to the transmit symbol sequence outputted by the S/P converter 43, and converts it into the n transmit symbol sequences . These n_τ transmit symbol sequence thus STBC encoded is inputted in the ^n IDFTs 45, and each IDFT 45 applies inverse discrete Fourier transform to the transmit symbol sequence thus inputted, to modulate it with a carrier of n_τ orthogonal frequencies. Moreover, the transmit symbol sequence thus modulated is serialized by the P/S converter 46, and after guard interval is inserted by guard interval inserter 47, transmitted from n_τ transmitting antennas 48. Meanwhile, each transmit symbol sequence transmitted form n transmitting antennas 48 of the transmitter 1' , is further transmitted to the receiver 30' via a fading channel, and received by the n_R receiving antennas 49, respectively. The receive symbol sequence received by each receiving antenna 49 is inputted in the guard interval remover 50 provided corresponding to each receiving antenna 49. The guard interval remover 50 removes the guard interval included in the receive symbol sequence. The receive symbol sequence removed by the guard interval is made to be parallel by the S/P converter 51, and separated into the receive symbol of N_sc carrier frequency components. Then>. after the DFT 52 applies Fourier transform to the receive symbol thus separated, the DFCE 53 decodes STBC-processed code, and thus the transmit symbol sequence is restored. The MRC 54 combines the restored transmit symbol sequence in a maximum ratio. The maximum ratio combining is the same process as that of the diversity receiver usually used. The transmit symbol sequence of N_sc columns obtained by the maximum ratio combining is serialized by the P/S converter 55, de-mapped by the de-mapper 56, de-interleaved by the de-interleaver 57, and convolutional decoded by the convolutional decoder 58, and thereafter outputted. Fig.4 is a block diagram illustrating the structure of the DFCE 53 of Fig.3. The DFCE 53 comprises a STBC decoder 60, a hard decision unit 61, an STBC encoder 62, a multiplier 63, a channel estimator 64, and a switcher 65. As described above, although the receive symbol sequence is input into the DFCE 53. The STBC decoder 60 restores the transmit symbol sequence including noise and error in channel estimation by decoding the STBC-processed code for the receive symbol sequence. The hard decision unit 61 performs hard decision for the transmit symbol sequence including noise, etc. , restored by the STBC decoder 60, and outputs a hard decision value of the transmit symbol sequence. The STBC encoder 62 encodes the hard decision value of the transmit symbol sequence into the STBC-processed code again in the same way as the STBC encoder 44, to generate a space time block code matrix G_p for the hard decision value of the transmit symbol sequence. Further, the STBC encoder 62 calculates an inverse matrix G_p ^_1 of the space time block code matrix G_p, and outputs it to a multiplier 63. The multiplier 63 multiplies the vector of the receive symbol sequence r_t ³ from the left of the inverse matrix G_P ^_1, and outputs a channel estimate matrix R_p ³ . Meanwhile, the channel estimator 64 outputs the channel estimate matrix H_p ³ by dividing the vector of the receive symbol sequence r_t ³ of a long preamble P_p as will be described later, by a long preamble Pp³. The switcher 65 selectively switches the channel estimate matrix H_p^ used by the STBC decoder 60 to the channel estimate matrix H_p^ outputted by the channel estimator 64 or the channel estimate matrix H_p ³ outputted by the multiplier 63. As for the communication system of the embodiment 3which was constructed like mentioning above, operations of the STBC encoder 44, the STBC decoder 60, and the DFCE 53 will be sequentially explained hereunder.

(2) STBC encoder First, the operation of the STBC encoder 44 of the receiver 30' in Fig.3 will be explained. As shown in Fig.3, the STBC encoder

44 is provided in a rear stage of the S/P converter 43 of the transmitter 1' . Therefore, output of the S/P converter 43 can be written as Eq. (38) as follows: i = [x_iιX , x_i;2 , • • • , x_i>k , • • • , x_iιN (38) where, i is the number of OFDM symbol, k is a sub-carrier number, and N_sc is the number of sub-carriers. Specifically, the transmit symbol sequence comprises N_sc sub-carriers per one OFDM symbol. The STBC encoder can be classified into two kinds such as the real signal type and the complex signal type, according to a modulation type and the number of the antennas . We denote the number of the symbols to be transmitted (transmit symbol) as , and time required for transmitting the transmit symbol as t. Then, an encoding ratio R can be written as Eq. (39) : =! (39) where the case of R=l calls full rate STBC, and the case of R=l/2 calls half rate STBC. The communication system as shown in the embodiment 3 of Fig.3 can be applied to both of the full rate STBC and the half rate STBC. Hereinafter, we specifically explaine the calculation process of the STBC encoder in the case of the full rate STBC and the half rate STBC.

(2-1) Full rate STBC A schematic view illustrating the full rate STBC encoder, which is an example of the STBC encoder 44 of Fig.3, is shown in

Fig.5. The condition under which the full rate STBC encoder '44' is realized is the case where Eq. (39) is established by R=l . The reason is that input symbols and output symbols of the STBC encoder can be simultaneously processed, as shown in Fig.5. The full rate STBC encoder 44' can be classified into two kinds as described bellow, according to the modulation type and the number n_τ of the transmitting antennas 48.

(1) BPSK; n_τ = 2, 4, 8

(2) QPSK, M-QAM; n_τ = 2

Hereinafter we will explain the above each case. (2-1-1) BPSK; n_τ = 2, 4, 8 As an example of the full rate STBC encoder 44' , we explain the case where the transmitting antenna is four. The overview of the full rate STBC encoder 44' is shown in Fig.5. The full rate STBC encoder 44' encodes input symbols using an encoding matrix, and outputs new symbols encoded in space-time block code. In the case of full rate STBC encoder 44' with n_τ=4, the encoding matrix can be written as Eq. (40) (see Ref .5) . The full rate STBC encoder 44' outputs the symbol sequence of each row of the encoding matrix to each IDFT 45.

Xi -X2 -X3 -X4. G₄ = X2 i X4 -X3 (40) X3 -X4 Xl 2 X4 X3 —X2 l

In the case of n_τ=2, 8, the encoding matrix can be written as Eq.s (41) and Eq. (42) (see. Ref.5).

Xi - 2 G2 — (41) X2 i i -X2 -X3 — 4 X5 -X6 -X7 — ₈

X3 4 Xi - 2 -x₇ - s x₅ Xβ G₈ = (42)

7 -Xs -X5 Xβ X3 -X Xi X2

(2-1-2) QPSK, M-QAM; n_τ = 2 In the case that the number of the transmitting antennas 48 is two (n_τ=2) , it is a specific case, and in this case, the full rate STBC can be applied not only to the real signals but also the complex signals (see Ref.6). In the case of n_τ=2, the encoding matrix can be written as Eq. (43) .

Also, other than this case, the encoding matrix can be written as Eq. (44) and Eq. (45).

(2-2) Half rate STBC The overview of the half rate STBC encoder 44", which is an example of the STBC encoder 44 of Fig.3, is shown in Fig.6. The condition under which the full rate STBC encoder 44" is realized, is that Eq. (30) is established as R=l/2. The reason is that, as shown in Fig.6, the time required for inputting symbols in the STBC encoder 44 until outputting it after encoded is twice of time needed for inputting symbols. In the case of the number n_τ of the transmitting antennas 48 is 3, 4, 8, and the case of the complex signals are treated like QPSK modulation or M-QAM modulation etc. , the STBC encoder 44 becomes half rate. As an example of the half rate STBC encoder 44", hereinafter we explain the case where the number n_τ of the transmitting antennas 48 is 4. An example of the half rate STBC encoder 44" of n^τ=4 is shown in Fig.6. The half rate STBC encoder 44" encodes the inputted symbols using the encoding matrix, and outputs the new symbols encoded in space-time block codes. In the half rate STBC encoder 44" of n^τ=4, the encoding matrix can be written as Eq. (44) (see Ref .5) .

Arbitrary two columns of the matrix of the right-hand side of Eq. (46) are orthogonal to each other. Note that the order of the column of the encoding matrix is the number n_τ of the transmitting antennas 48, and the order of the row is the time needed for transmitting the symbols. The half rate STBC encoder 44" outputs the symbol sequence of each row of the encoding matrix to each IDFT45. In the case of the number n_τ of the transmitting antennas 48 is 3 and 8, the encoding matrix can be written as Eq.s (47) and Eq.

(48) .

Xl —X₂ —X3 — 4 —X₂ —X3 — 4 GS X₂ Xl X4 -X3 X| X* X4 -^χ3 (47)

i -X2 - 3 —X₄ -Xs - β -X7 -xs _i -X2 -xl -*4 -^χl - β -x₇ -xi X2 Xi -X X3 - β X5 xs -X7 Jt₂ xϊ - x₃ -^χ ₆ ^x5 s — ₇ X3 X i -X2 -x₇ -xs xs G x χ₄ χl -χ₂ -x₇ -^x? x| xβ G% X4 -X3 2 i -Xs x₇ -xβ X5 x₄ -X3 ^X*2 xϊ -^χ ₈ x₇ -^χ ₆ X5 5 xe x₇ s l -X2 -X3 -X4 ^χ ₅ xg x₇ xϊ -4 —x₃ -X4 β - s Xs -X7 2 xi X4 -X3 χ -X5 xs -? 2 xj j -*s X7 -xs -X5 Xβ X3 -X₄ Xi X2 x₇ -xl -xs X3 - xi χ| s X7 - β -X5 X4 X3 -X2 i g X? -^χ ₆ -xs xl -^X2 xϊ (48)

(3) STBC decoder (see Tef.7)

Next, we explain the operation of the STBC decoder 60 in Fig.4. The receive signal received with each receiving antenna 49 in the receiver 30' undergoes influenced by the channel (transmission path). A channel model of the communication system of Fig.3, is shown in Fig.7. As shown in Fig.7, in the case that the transmit symbols transmitted from the n_τ transmitting antennas 48 is received with n_R receiving antennas, n_τ x n_R transmission paths can be assumed. The receive symbol τ_t ³ which is received via each transmission path, is represented as the total amount obtained by the sum of the convolutional output between the transmit symbol x_x transmitted from each transmitting antenna 48 and the channel constant H_p ¹, added with additive white Gaussian noise (referred to as "AWGN" hereafter) n_t ³. Where, p is the index of the transmitting antennas, j is the index of the receiving antennas 49, and t is the time for receiving the 1 OFDM symbols. In addition, each element of r_t , H_p ^x, n^ can be written as Eq. (49), Eq. (50), and Eq. (51). r* = Kι>' --,» --, i_VJ (49) H^^,^,...,^...,^^] (50) n« = Ki. 2> ^••■ "*_*.-^•• , ΛΓJ (⁵¹) where, k is a sub-carrier number, and N_sc is the total number of the sub-carriers. A channel is estimated by a long preamble in the DFCE 53 of Fig.4 for the receive symbol r_t ³ received by the receiving antenna 49, and feedforward is applied to the estimate value of a channel constant H_p ^j via the switcher 65. The STBC decoder 60 performs a maximum likelihood decoding, based on the channel estimate value. Thereafter, the transmit symbol restored by each receive branch (the guard interval remover 50, the S/P converter 51, the DFTs 52, and the DFCEs 53 are mentioned) is combined in a maximum ratio and de-mapped by the MRC 54. Note that the number n_τ of the transmitting antennas 48 is limited according to the case such as the full rate STBC and the half rate STBC. However, the number n_R of the receiving antennas 49 is arbitrary in each case. Next, specific operation of the STBC decoder 60 will be explained in each case of the full rate STBC and the half rate STBC.

(3-1) Full rate STBC In the case of the full rate STBC, as described before, the case where the number n_τ of the transmitting antennas 48 is 2, 4, 8 is considered. Here, as the example, we describe the case of n_τ=4. We denote The receive symbol obtained by receiving the transmission signals transmitted from four transmitting antennas of the transmitter 1' and received by each receiving antennas 49 through the channel (transmission path), as r_t ³ • j is the index of the receiving antenna 49, and t is the time of the receive symbol. The receive symbol is expressed by r_t ³ can be written as Eq. (52]

where, a receive signal matrix R-_j, a channel matrix E_p , a transmission signal matrix G_p, and a noise matrix ₃ are respectively expressed by Eq. (54) , Eq. (55) , and Eq. (56) .

Then, Eq. (52) can be represented by a general equation such as Eq. (57) . R³ = HG_P + FP (57) The STBC decoder 60 performs maximum likelihood decoding so as to restore the transmission signal from the receive signal. In the case of the full rate STBC where the number n_τ of the transmitting antennas 48 is four, the decision value of the transmission signal can be written as Eq. (58) . 4 n_R (58) p=l =1

Here, index ε _t (i) in H _{ε t}u)³ is the position of x_x at time t. Specifically, when t denotes the column number of each column of the encoding matrix G, and considering that the column t in the encoding matrix G is permutation which is accompanied by sign conversion of column 1 in the encoding matrix G, ε _t(i) is the row number of the element in column 1 corresponded to i-th row element in column t. In addition, sgn_t (i) denotes a polarity of x_x at time t. Specifically, when t denotes the column number of each column of the encoding matrix G, and considering that the column t in the encoding matrix G is permutation which is accompanied by sign conversion of column 1 in the encoding matrix G, sign_t(i) is the sign conversion between a i-th row element in column t and element in column 1 corresponded to it . H_p ³ is a channel constant and can be obtained by the channel estimation. When Eq. (58) is applied to the communication system where the number n_R of the receiving antennas 49 is four, the transmission signal x decoded by each receive branch can be written as Eq. (59) to Eq. (62) . xi = £(ri(Hi + ri(Hr +

+ ri(H)*) 3=1 (59) pxi + £ (ni(Hi)* + n(H)* + ni(H|)' + n(H)*) ₃=1

X2 = £(ri(Hi)*-ri(Hi)*-ri(H)* + r(Hr) 3=1 (60) .= px₂ + £ (ni(Hi)* - ni(H)* - nJ(H$)^« + ni(Hi)*) J=l

X₃

X₄ = (ri(Hi)*-r^J ₂(H)* + r(Hir-ri(Hi)*) 3=1 (62) = pxi + ∑ (ni(H)* - n(H)* + ni(H^J ₂)* - n(Hi)*) 3=1 where, p is a transmitter/receiver diversity gain, and expressed by Eq . ( 63 ) .

From the above-described equations, the transmit symbol influenced by the channel is set back, and the transmit symbol can be restored. x. = - (64) P

Note that when Eq. (58) and Eq. (63) are generalized by setting the number of the transmitting antennas 48 to be n_τ, and setting the number of the receiving antennas 49 to be n_R, they are expressed by Eq. (65) and Eq. (66) .

p=l j=l

(3-2) Half rate STBC In the case of the half rate STBC, the number n_τ of the transmitting antennas 48 is considered to be three cases of 3, 4, 8. Here, the case of n_τ=4 is explained as an example. The receive symbol obtained by receiving the transmission signal transmitted from four transmitting antennas 48 of the transmitter 1' by each receiving antenna 49 through the channel (transmission path) , is denoted as r^ . j is the index of the receiving antennas 49, and t is the time of the receive symbol. The receive symbol r_t ³ can be written as Eq. (67) . ^> (67) ^* * *

^* Here, if the index j of the receiving antennas 49 is fixed value, the decision value of the transmission signal can be written as Eq. (68) to Eq. (70) when the half rate STBC is conducted by four transmitting antennas 48. x. = ∑∑s<7«t(*) ' ^•ϊξtø (68) p=l =1 τ³ _t if j belong to Ihe t-th column of X (69) (rj)* if (x,)* belong to the i-th column of X

• _j . . J (H_gf )*(«) if j belong to the t-l column of X (70) -.W - j U'^i) if x^* belong to the t-th column of

When Eq. (68) is applied to the ^communication system where the number n_R of the receiving antennas 49 is four, the transmission signal x_x decoded by each receive branch can be written as Eq. (71) to Eq. (74) .

"Λ i = ∑ (ri(Hi)* +ri(Hi)* +rj )* +ri(H₄)* + {4)*H\ + tørø + (r₇)*Hi + (ri)*H₄) 3=1 = px.r + ∑ (ni(Hi)* + n(Hi)* +n(Hi)* + ni(H)* + (n|)*Hi + K)*H| + (n₇)*Hi + (ni)*H₄) 3=1 (71) 2 - ∑ (ri(H|)* - r^> ₂(Hi)* - i(Hj)* + ri(H^J ₃)* + (rJ)^«H£ - (r^Hi - (r₇)*Hi+ (r|)*Hi) 3=1 = _/>x₂ +∑ (nJ(HS)* - n₂(Hi)* - ^(H^)^* + njrø)* + )*H'₂ - (n|)*Hi - tø)"H^> + (n|)O0 3=1 (72) xs = ∑ (ri(H )* + ι (H )* - rJ(Hi)- - ri(H|)* +

- ( )^*ff₂)

X₄ = ∑ (ri(Hi)* - r (H^)* + ri(H₂)* - r (H )* + (ι )^*H - K)^*H^ + (r₇)^*H₂ - (ri)^*Hi) 3=1 n_R = _PX4 + ∑ (ni(Hi)* - ni(Hi)* + n rø - n (Hi)^* + (n )*H - )Ηi + (n₇)*Hi - (πrø) 3=1 (74)

Here, p is a transmitter/receiver diversity gain and written as Eq. (75) .

^

From the above equations, the transmit symbol influenced by the channel is set back and the transmit symbol can be restored by the above Eq. (64) . Note that when Eq. (68) and Eq. (75) are generalized, by setting the number of the transmitting antennas 48 to be n_τ, and setting the number of the receiving antennas 49 to be n_R, they can be written as Eq. (76) and Eq. (77) .

*_* = ΣΣ^s *)-r-H^J ₆ ) (76) p=l ₃=1

(4) Decision feedback channel estimator Finally, explanation will be given to the operation of ² the DFCE 53 in Fig.4 when the channel estimate value is actually derived. In the DFCE 53 of the communication system in Fig.3, improvement of precision in channel estimation is accomplished by conducting two channel estimation such as the channel estimation by long preamble and the decision feedback channel estimation (DFCE) . The detailed explanation will be given hereunder according to the flow of the actual signal. The structure of the DFCE 53 and the structure of the training signal is shown in Fig.4. The long preamble is inserted after a short preamble and in the data sequence. The communication is conducted by repeating the transmission of the training signals plural times. The channel estimation is conducted at the part of the long preamble in the training signals and at the part of the data sequence, . Iteration number of the channel estimation is denoted as i, hereunder.

(4-1) Channel estimation by long preamble In the case of i=l, the channel ^' stimator 64 estimates the channel by the long preamble. At this time, the switcher 65 is connected so as to input the channel estimate value H_p ³ outputted by the channel estimator 64 in the STBC decoder 60. A channel estimation method by the long preamble is explained in the embodiment 1, however, the more general case will be explained here. The method is to estimate a signal amplitude attenuation and an amount of phase rotations caused by influence of the channel, using the characteristic that a long preamble pattern is known between a transmission side and a receive-side. ' When a long preamble sequence is defined as P_p ³, and the channel estimate value is defined as H_p ³, the channel estimator 64 calculates the channel estimate value Rp³ by Eq. (7

^W = S^Λ (p = l, - - - ,nτ, k = l, - , N„) (78) I ^pl where, the long preamble sequence P_p can be written as Eq. (79) .

Pp — [-Pp,l> Pp,2i - " ' ) Pp,k! " ' ' i Pp,NsΔ ®)

(4-2) Decision feedback channel estimation In the case of i=2, by STBC decoding by the STBC decoder 60 using the channel estimate value _p obtained by the channel estimation using the above-described long preamble, the transmit symbol x_x is decoded from the receive symbol r-³. At this time, the switcher 65 is connected so as to input the channel estimate value H_p ³ outputted by the multiplier 63 in the STBC decoder 60. The hard decision unit 61 performs hard decision of the transmit symbol x-_. and outputs the hard decision value described as : * x, (80)

The STBC encoder 62 encodes the STBC-processed code again by using the hard decision value thus obtained, generates a hard decision value transmit symbol matrix expressed as: G_P (81) The STBC encoder 62 outputs the inverse matrix of the hard decision value transmit symbol matrix expressed as: G¹ (82) to the multiplier 63. By multiplying the receive signal matrix R-, by the inverse matrix of the hard decision value transmit symbol sequence like: R' - ^- ^ (α = l or 2) . .

from the left hand side, the multiplier 63 calculates the channel estimate matrix by hard decision expressed as:

H£ = G;¹.R' (84)

and outputs the value thus obtained to the switcher 65. The switcher 65 outputs the channel estimate matrix (Eq. (84) ) to the STBC decoder 60. Note that in Eq. (83), α=l is established for the full rate STBC, and α=2 is established for the half rate STBC. The above-described estimation method is called a "decision feedback channel estimation (SFCE) method". The above-described channel estimate matrix outputted by the switcher 65 is used when the STBC decoder 60 estimates the channel by STBC in the next iteration. Thus, the STBC decoder 60 can follow after the channel variation in the data sequence, and the precision in decoding the transmit symbol is improved. In the case of 3≤i≤D_Lp-l (where D_Lp is the iteration number to cause the next long preamble to be appeared) , the decision feedback channel estimation is conducted in the same way as the above-described i=2. At this time, the STBC decoder 60 decodes the STBC-processed code by using the channel estimate matrix by hard decision calculated in the previous iteration. A series of the operation of the DFCE 53 as described above can be assembled as follows: '

(1) i=l : Estimation of the channel estimate matrix H_p ^j by long preamble. (2) i=2 to D_Lp-l : Estimation of the channel estimate matrix H_p ^j by decision feedback. (3) i=D_LΪ>: Estimation of the channel estimate matrix E_p ³ by long preamble. (4) i=D_LP+l to 2D_LP-1 : Estimation of the channel estimate matrix H_p ³ by decision feedback. (Similarly repeated hereunder) .

(Embodiment 4) In an embodiment 4, the communication system provided with n_τ transmitting antennas and n_R receiving antennas will be explained.

[1] Structure of the communication system Fig.8 illustrates the structure of the communication system according to a fourth embodiment of the present invention. Fig.8 (a) shows a transmitter 1", and Fig.8(b) §hows a receiver 30". When the transmitter 1" of Fig.8 is compared with the transmitter 1' of Fig.3, difference is that an SFBC encoder 70 is used in the transmitter 1" of Fig.8, instead of the STBC encoder 44 used in the transmitter 1' of Fig.3, however the other part is the same. Also, when the receiver 30" of Fig.8 is compared with the receiver 30' of Fig.3, only the DFCE 53' is different therebetween, and the other part is the same therebetween. The SFBC encoder 70 encodes the transmit symbol sequence outputted by the S/P converter 43 into a space frequency block code (referred to as space-frequency block code) , and converts it into the transmit symbol sequence Of n_τ columns . Fig.9 is a block diagram illustrating the structure of the DFCE 53' of Fig.8. When the DFCE 53' of Fig.9 is compared with the DFCE 53 of Fig.4, difference is that a SFBC decoder 71 and a SFBC encoder 72 are used in the DFCE 53' , instead of the STBC decoder 60 and the STBC encoder 62 used in the DFCE 53 of Fig.4, and the other part is the same therebetween. The SFBC decoder 71 functions to decode the SFBC-processed code for the receive symbol sequence, and restore the transmit symbol sequence including noise and error in the channel estimation. As for the communication system according to the embodiment 4 structure as described above, the operation of the SFBC encoder 70, the SFBC decoder 71, and the DFCE 53' will be sequentially explained hereunder.

[2] SFBC encoder First, the operation of the SFBC encoder 70 of the transmitter 1" of Fig.8 will be explained. The SFBC encoder 70 is provided in the rear stage of the S/P converter 43 of the transmitter 1" as shown in Fig.8. Therefore, output of the S/P converter 43 is described by Eq. (85) . x(i) -= [x_x(i), x₂(i), • • • , -Cfc(ϊ), • • • , x_NlK!(ϊ)] (85) where, i is an OFDM symbol number, k is a sub-carrier number, N_sc is the total number of the sub-carriers. This means that the above symbol sequence comprises N_sc data sub-carriers per one OFDM symbol. ' The SFBC encoder can be classified into two kinds such as the full rate encoder and the half rate encoder, according to the modulation type and the number of the antennas . Note that difference between the STBC and SFBC is that STBC encodes by OFDM symbol unit, while SFBC encodes by sub-carrier unit in one OFDM symbol.

(2-1) Full rate SFBC The condition of the SFBC encoder 70 is that Eq. (39) becomes 1 in the same way as STBC. The reason is that, as shown in Fig.10, the input symbol and the output symbol of the SFBC encoder can be simultaneously processed. The full rate SFBC encoder 70' can be classified into the following two kinds, according to the modulation system and the number n_τ of the transmitting antennas 48. (1) BPSK; n_τ=2,4,8 (2) QPSK, M-QAM; n_τ =2

Above each case will be explained hereunder.

(2-1-1) BPSK; n_τ =2,4,8 The full rate SFBC encoder 70' encodes the input symbol according to the encoding matrix, and outputs the new symbol. In the case of the actual signal, the encoding matrix transmitted from each transmitting antenna 48 is, for example, expressed by Eq. (86) ,

Eq. (87) , and Eq. (88) .

G₂ = ^x2n — ^x2n+l (86) ^x2n+l ^x2n Xin — £4n+l — ^x4n+2 —^χ4n+3 ^4n+l ^x4n ^x4n+3 ~^x4n+2 G₄ (87) ^x4n+2 2-4n+3 ^x4n ^x4n+l ^4n+3 &4n+2 ^_ #4n+l Xin %n —XSn+1 —^χSn-\-2 — £S +3 — £8τι+4 -£871+5 — £8n+6 — £₈n+7 &871+1 ^x8n — £8n+3 871+2 — £8τι+5 £δn+4 £8τι+7 — £₈n+6

— XSn+β — 8ιι+7 £8n+4 £8τι+5 G₈ = £8n+3 — ^871+2 ^Sπ+1 ^xSn — £₈n+7 £8n+6 — Xsn+5 £8τι+4 (88) £8τι+4 ^x8n+5 ^Sn+β 8 +7 8n — ^877+1 — 8n+2 — £8n+3 £8re+5 —^χ8n+4 £Sτι+7 — 871+6 £8n+l ^x8n £8τι+3 — £8n+2 £8n+6 — ϊ8n+ — 8n+4 £₈n+5 X8n+2 — £8n+3 $871 X&n+l #8π+7 ^xSn+6 —^871+5 — £8τι+4 £8τι+3 £8n+2 — #871+1 8n where, the order of column of the encoding matrix is the number n_τ of the transmitting antennas 48, the order of row is the number N_sc of sub-carriers. In addition, the element of each encoding matrix shows the sub-carrier in one OFDM symbol, and the equation expressed by n=0,l,2,..., (N_sc/n_τ) -1 is established. Also, since the same processing is conducted in each coding matrix, the OFDM symbol number i is omitted.

(2-1-2) QPSK, M-QAM; n_τ=2 As an example of the full rated SFBC encoder 70' , explanation will be given to the case where the complex signals are treated under condition that the number n_τ of the transmitting antenna is two. Fig.10 is a schematic view illustrating an example of the full rate SFBC encoder 70', which is one of the SFBC encoders 70 in Fig.8. The full rate SFBC encoder 70' encodes the input symbol according to the encoding, matrix, and outputs the new symbol. In the full rate SFBC, the encoding matrix transmitted from each transmitting antennas 48 can be written as Eq. (89) . GS = 2 — £2n+l (89) £2n+l 2

(2-2) Half rate SFBC When the number n_τ of the transmitting antennas is 3, 4, and 8, and when the complex signals are treated by QPSK modulation and M-QAM modulation, the SFBC encoder 70 becomes half rate. The reason is that two times amount of information is required for the input symbol of the SFBC encoder 70, until the encoded symbol is outputted. Therefore, Eq. (30) can be written as R=l/2. The half rate SFBC encoder 70 encodes the input symbol according to the encoding matrix, and outputs the new symbol. In the half rate SFBC encoder 70, the encoding matrix transmitted from each transmitting antenna 48 can be written as Eq. (90) to Eq. (92) . ^x4n — £₄n+l — £ i+2 —£4n+3 £41 ^41+1 — £41+2 —^•£41+3 GS = £4re+l 4n £4n+3 — £4n+2 ^X4n+1 T4*n 71+3 —£477+2 (90) ^x4n+2 — 4 +3 £477 £4n+l

— 4 +3 ,£41 ^x4n+l ^x4n — £4n+l — £4n+2 — £₄7i+3 £4τι — 41+1 —£ 1+2 —£477+3 £4n+l 4 £471+3 — £4?ι+2 £471+1 £477 £471+3 —£₄7i+2 G\- (91) £4n+2 — £₄τι+3 £471 £4n+l £471+2 £477+3 ^•^471 £471+1 X4n+3 £4n-12 — 471+1 £ 71 471+3 4n+2

£8τι — £8τι+l ~^x8n+2 — £8n+3 — £8?!+4 — £8τι+5 — £8n+6 — £8n+7 £8n+l £8 — £8n+3 £8n+2 — £8Λ+5 £8n+4 £8n+7 — £8τι+6 £8τι+2 £8n+3 8n — £8n+l — £8n+6 — £8n+7 £8n+4 £8n+5 £8τι+3 — £8τ+2 GS = £8n+l £8n — £8n+7 £877+6 — £8n+5 £8n+4 £8n+4 £8τι+5 £871+6 £871+7 £8τι ^— £877+1 — £Sτt+2 —£87i+3 £8n+5 — £8τι+4 £8τι+7 — £8n+6 £8n+l £8τι £87+3 — £8n+2 £8n+6 — £8τι+7 — £8n+4 £8τι+5 £8τι+2 — £8n+3 87 £8n+l £8τι+7 £8τι+6 — £8τ+5 — £8n+4 £8τι+3 £Sτι+2 — £8τι+l £8τι (92) ^•''Sn ^— ^δ +l ^■^81+2 -£8τ+3 ^■^871+4 ^— £877+5 ^{— X}8TI+6 ^_£8τι+7 £S +l 8n — sn+3 £8τι+2 - 8n+5 8 +4 ^X8n+7 — £8τι+6 8τι+2

Sn+3 ^_ 8τι 12 £8τι+l £8τι ~£8τ»+7 £8τιl6 £8τH5 8nl 8τι+4 ^βn+δ ^X8n+6 8 +7 ^x8n — £8τι+l ^_iE87i+2 ~^X8n+3 £8n+5 ^_a;8n+4 8n+7 ^_ 8i+6 8τιHl 8» ^X8ni-3 ^— 8n+2 8τι+6 ^~X8n+7 ^_£8τι+4 8τι+5 £sn+2 — 8τι+3 ^X8n ^X8π+1 £8τ7+7 ^X8n+6 £8τι+5 ~ £8 +4 8n+3 £8τι+2 ~^x8n 1-1 8n . where the order of the column of the encoding matrix is the number n_τ of the transmitting antennas, and the order of the row is the number N_sc of the sub-carriers. In addition that an element of each encoding matrix expresses the sub-carrier in one OFDM symbol, and the equation expressed by n=0, 1,2, ..., (Nsc/2n T) -1 is established. Also, since the same treatment is conducted in each encoding matrix, the OFDM symbol number i is omitted.

[3] SFBC decoder

Next, the operation of the SFBC decoder 71 of Fig.9 will be explained. The receive signal received by each receiving antenna 49 is received influenced by the channel (transmission path) . A channel model in the communication system of Fig.8 is shown in Fig.7. As shown in Fig.7, when the sub-carriers transmitted from n_τ transmitting antennas 48 is received by n_R receiving antennas 49, the transmission path of n_τ x n_R can be assumed. The receive symbol ry received through each transmission path is expressed by the sum of the transmit symbol x_x transmitted from each transmitting antenna 48 and the convolutional output of the channel constant H_p,*¹, added with additive white Gaussian noise (referred to as AWGN hereafter) n^ . Here, p is the index of the transmitting antenna 48, j is the index of the receiving antenna 49, and k is the index of sub-carriers . In addition, each element of r_k ^j, H_p^¹, and n_k ^j can be expressed by Eq. (93), Eq. (94), and Eq. (95), respectively. ή = HΛ- ⁽⁹³⁾

Hik = [ i> ^Hi,2> - - - , H (94)

ⁿ*=[ⁿl."2. ^••-.»%.] (⁹⁵) where k is the sub-carrier number, and N_sc is the total number of the sub-carriers . A channel is estimated by a long preamble in the channel estimator 64 of the DFCE 53' of Fig.9^sfor the receive symbol r^ received by the receiving antennas 49, and feedforward is applied to the estimate value of the channel constant H_p]c ^j in the SFBC decoder 71 via the switcher 65. The SFBC decoder 71 decodes the above receive symbol based on the channel estimate value. Thereafter, the transmit symbol restored by each receive branch (the guard interval removers 50, the S/P converters 51, and the DFTs 52, and the DFCEs 53' , which corresponds to each receiving antennas 49) is combined in a maximum ratio by the MRC 54, and de-mapped. Note that as for the number n_τ of the transmitting antertnas 48 is limited in both cases of the full rate SFBC and the half rate SFBC. However, the number n_R of the receiving antennas 49 is arbitrary in the above either case. Next, the specific operation of the SFBC decoder 71 will be explained in the full rate SFBC and the half rate SFBC.

(3-1) Full rate SFBC In the full rate SFBC, as described above, the number n_τ of the transmitting antennas 48 can be 2, 4, 8. Here, a complex signal when n_τ=2 is established is explained as an example. The signal of the sub-carrier obtained by receiving the transmission signal transmitted from two transmitting antennas 48 of the transmitter 1" through the channel (transmission path) by each receiving antenna 49 is described as rj . j is the index of the receiving antenna 49, and k is the index of the sub-carrier. The receive symbol can be written as r^ by Eq. (96) .

' 2n ϊ,2τι ^" 2,2τι ^x2n (96) (^r2τι+l) (^• 2,271+1 )* ( ϊ,2»+l)* £2n+l + ™ +ι

The transmission signal can be restored from the receive signal, by multiplying the receive signal matrix by the inverse matrix of the channel matrix of Eq. (96) from the left hand side, thereby deriving it. In the case of the full rate SFBC wherein the number n_τ of the transmitting antennas 48 is two, the decision value of the transmission signal x^ (i) can be calculated by Eq. (97) . -1 r £₂n ⁿ Hl³,2n —-#2,2 ^r2n ^x2nΛ l ( 2,2τι |-l)* (#1,277+1)* ('^"in+l) 1 0 £2n ( l,2τι+l)* #2,2τι '2n 0 1 £2τι+l + -"l,27 ( l,2τι+l)* + - 2,2τι( 2,2n+l)* — (- 2,2n+l)* #l,2n TV '2, J nH l 1 0 0 1

(97) From the above-described equations, the symbol influenced by the channel can be set back and the transmission symbol can be restored.

(3-2) Half rate SFBC In the case of the half rate SFBC, the number n_τ of the transmitting antennas 48 is considered to be three cases of 3, 4, 8. Here, the case of n_τ=4 is explained as an example. The receive symbol obtained by receiving the transmission signal transmitted from four transmitting antennas 48 of the transmitter 1" through the channel (transmission path) by each receiving antenna 49 is described as r_k ³. j is the index of the receiving antenna 49, and k is the index of the sub-carrier. The receive signal r^ can be written as Eq. (98) .

H ⁿ ft8³n \ l - f"t8³77+2 #8τι+3 ^" ni_n — ⁿ TJ8³n+l τt³ — - f"tS³n+3 #8n+2 ⁿ8τι+l — - f"t8³71+2 #8τι+3 - τ"-r8³71 — ⁿ ft 8³71+I £4π "8τι+2 — #8τι+3 — #8n+2 - f"t8³n+i H £4n+l + "877+3 (98) (-#871+4)* (#877+5)* (#8τι+6)* (-#871+7)* £4rι+2 ⁿ8n+4 — (#871+5)* H HT — (#8711 )* (#In+6)* £4n+3 8n+5 — (#877-1 6)* H +rY (-#877+4)* -(# n+₅)^* X "8n+6

. —(#877+7)* -(#ln+₆)^* (#871+5)* (#871+4)* . . "Sn+7 . R^J H^J N³ When generalizing Eq. (98) , setting the receive signal matrix to be R-_j, setting the channel matrix to be H^D, setting the transmission signal matrix to be X³, and setting the noise matrix to be N³, the receive signal matrix can be expressed by Eq. (99) . R³ = W ■ X + N³ (99) By multiplying the receive signal matrix R-, by the inverse matrix of the channel matrix H-, from the left hand side of Eq. (99) , the transmitted signal can be restored from the receive signal. X = (H³)-¹ ■ R^j (100)

By using the above-described methods, the transmitted signal can be similarly restored in the case other than the case of n_τ=4.

[4] Decision feedback channel estimator Finally, explanation is given to the operation of the DFCE 53' of Fig.9 when the channel estimate value is actually derived. In the DFCE 53' of the communication system of Fig.9, improvement of precision in channel estimation is realized by conducting two channel estimation such as the channel estimation by long preamble and the decision feedback channel estimation. The detailed explanation will be given hereunder according to the flow of the actual signal. Fig.9 illustrates the structure of the DFCE 53' and the structure of the training signal. The long preamble is inserted after the short preamble and in the data sequence. The communication is conducted by repeating the transmission of the training signals plural times. The channel estimation is conducted at the part of the long preamble and at the part of the data sequence, during transmitting the training signals. Iteration number of the channel estimation is defined as i, hereunder.

(4-1) Channel estimation by the long preamble ' When i=l is established, the channel estimator 64 estimates the channel by the long preamble. At this time, the switcher 65 is connected so as to input the channel estimate value R_Ptι? (i) outputted by the channel estimator 64, in the SFBC decoder 71. The method of the channel estimation by the long preamble is to estimate a signal amplitude attenuation and an amount of phase rotations caused by influence of the channel, using the characteristic that a long preamble pattern is known between a transmission side and a receive-side. When the long preamble is defined as P_p ³, and the channel estimate value is defined as Hp,^ (i) , the channel estimator 64 calculates the channel estimate value H_p,_k ^j (i) by Eq. (101) . A^ = l rf (P = - - - ,n_τ, k = l, - - - ,N_sc) (101)

Here, the long preamble sequence P_p ^j can be written as Eq. ( 102 ) .

**.> ⁼ r p,i' Ip, > ' " ^■>

(102)

(4-2) Decision feedback channel estimation When i=2 is established, by using the channel estimate value H_p,]^ (i) obtained by estimating the channel using the above-described long preamle, the SFBC decoder 71 decodes the SFBC-processed code, thereby decoding the transmission signal x_k(i) from the receive signal r^ . At this time, the switcher 65 is connected so as to input the channel estimate value H_p,_k ^j outputted by the multiplier 63 in the SFBC decoder 71. The hard decision unit 61 performs hard decision for 'the decoded signal x_k(i) from the SFBC decoder 71, and outputs the hard decision value expressed as: **(*) (103)

The SFBC encoder 72 encodes the SFBC-processed code again by using the hard decision value thus outputted, and generates the hard decision value matrix expressed as:

G„ (104)

The SFBC encoder 72 outputs the inverse matrix of the hard decision value matrix expressed as:

-1 G (105)

The multiplier 63 can obtain the new channel estimate value expressed as:

by multiplying the receive signal r_k^ by the inverse matrix of the hard decision value matrix from the left hand side. Finally, the case where the number n_τ of the transmitting antennas 48 is two, is given as an example. The receive signal can be written as Eq. (96) . If the Eq. (96) is replaced, Eq. (107) is obtained.

#tan( n») -#2,2n(2™) £2n (107) K,.₊ι)^* (i ι)^*H (#ι,2„+ι)^*(2m) £2τι+l + "in n '2, 71+1

For simplification, if the noise component is ignored, Eq. (108) is obtained. (2 ) (ri_n+ι)*(2m)

Here, (2m) is the OFDM symbol number, and equation m=0,l,2,..., n_τ_ι is established. The inverse matrix after hard decision can not be derived from the transmission matrix in the above .equation. Therefore, when two continuous OFDM symbols are received, and if an approximation can be written as H_p,^ (2m) ^H_p,^ (sm+1) , the channel matrix H_p^ can be degenerated like Eq. (109) .

W p = #l,2n (#2,2τι+l)* (109) —#2,2τι (#l,2n+l)* Therefore, Eq. (108) can be expressed by Eq. (110)

Here, the receive signal matrix is defined as Rj , the channel matrix is defined as H_p^, and the transmission signal matrix is defined as G_p. From the above equations, the hard decision value matrix (Eq. (105) ) between two OFDM symbols can be derived, and by multiplying the receive signal matrix R^s ₃ by the hard decision value matrix thus derived from the left hand side, the channel estimation value by hard decision (Eq. (106)) is obtained by Eq. (Ill)

* j ~ — 1 H_p = G_p R³ (111)

Industrial Applicability According to the present invention, in a STBC demodulating step, it becomes possible to suppress the influence of the frequency selective fading environment and the time selective fading environment given on the error property of communication, by demodulating a symbol sequence X_n' of each block, using a transfer function matrix H constituted based on a transfer function estimated for each block and for each sub-carrier. Therefore, even in a case of a communication between mobile objects at a high rate, or in a case of sharply varying temporal fading environment such as a communication between mobile objects which move at high speed, it becomes possible to suppress the deterioration in error property. In addition, after the transfer function in transmitting foremost two blocks of a symbol sequence X is initially estimated by using a preamble, by alternately repeating a hard decision step and a transfer function updating step, adaptively to the momentarily varying fading environment, a symbol sequence X_n' can be demodulated while varying the estimate value of the transfer function. Accordingly, it is possible to provide a communication technology capable of accurately demodulating the symbol sequence, even if the time selective fading is significantly present.

Claims

1. A communication method for conducting wireless communication of a transmit symbol sequence between a transmitter and a receiver by conducting wireless communication from n_τ (n_τ≥2)

^■ transmitting antennas by a transmitter diversity system after dividing a transmit symbol sequence into blocks comprising a prescribed number of symbols, and encoding them by space-time block coding (referred to as "STBC" hereafter) or space-frequency block coding (referred to as "SFBC" hereafter) for each block in a transmitter, and demodulating the transmit symbol sequence based on a receive symbol sequence obtained by receiving wireless signals transmitted from each transmitting antenna by n_R (n_R ≥l) receiving antennas, and the communication method for conducting wireless communication of the transmit symbol sequence by repeating decision feedback channel estimation process, comprising: a first step of estimating the transmit symbol sequence by decoding STBC-processed codes or decoding SFBC-processed codes by hard decision, based on the value of each transfer function previously stored in a transmitting function storage part and each of the receive symbol; a second step of estimating the value of the transfer function of each channel by dividing a vector whose element is a receive symbol per unit block (referred to as "transmit symbol vector") , by a vector whose element is a transmit symbol sequence per unit block estimated by the first step (referred to as "receive symbol vector") ; and a third step of updating the value of the transfer function stored in a transfer function storage part to the value of the transfer function estimated by the second step, when the second step estimates the value of the transfer function.

2. The communication method according to claim 1, comprising: in a transmitter, dividing a transmit symbol sequence for transmitting from the transmitter to a receiver, into data flames comprising a prescribed number of blocks; alternately transmitting a preamble comprising a symbol sequence of known pattern (referred to as "training sequence" hereafter) and the data flame as a transmit symbol sequence; in a receiver, when the preamble is received, estimating the value of the transfer function of each chanhel by dividing a vector whose element is a receive symbol of the preamble, by a vector whose element is a training sequence of a known pattern; storing the value of the transfer function in the transfer function storage part; and conducting wireless communication of the transmit symbol sequence by repeating the decision feedback channel estimation process, when the data flame is received.

3. The communication method according to either of claim 1 or claim 2, comprising: ' in the transmitter, generating an OFDM symbol by modulating an STBC-processed symbol sequence by an orthogonal frequency division multiplex (referred to as "OFDM" hereafter) system; thereafter, conducting wireless communication from n_τ (n_τ≥2) transmitting antennas by a transmitter diversity system; and in the receiver, generating a receive symbol sequence for wireless signals transmitted from each transmitting antenna, by conducting demodulation of OFDM for the received OFDM symbol sequence received by n_R (n_R-≥l) receiving antennas; and based on the receive symbol sequence, demodulating the transmit symbol sequence.

4. A communication method, comprising: an STBC-processing step of performing STBC-processing for generating two mutually orthogonal symbol sequences X_n ^A and X_n ^B comprising M sub-carriers by dividing a transmit symbol sequence X into blocks comprising M (M≥2) sub-carriers, and based on the symbol sequence X_n (n=0, 1,2,.... , n is a block number) of each block thus divided; a transmitting step of transmitting each of the symbol sequences X_n ^A and X_n ^B for modulating each of the symbol sequences

X_n ^A and X_n ^B by an OFDM system and transmitting the symbol sequences thus demodulated from two spatially different transmitting positions by a transmitter diversity system; an OFDM demodulating step of demodulating OFDM 'for demodulating a receive signal by applying discrete Fourier transform thereto obtained by receiving signals transmitted by the transmitting step at one receiving position, thereby generating a receive symbol sequence R_n comprising M sub-carriers; and an STBC demodulating step of demodulating STBC-processed codes for demodulating a symbol sequence X_n' of each block by using the receive symbol sequence R_n for inverse matrix H^_1 of transfer function matrix H, which is constituted based on the transfer function estimated for each block and for each sub-carrier by a prescribed estimation method, and by which the receive symbol sequence R_n is related to the symbol sequence X_n.

5. The communication method according to claim 4, comprising: a preamble transmitting step of transmitting preambles for transmitting symbol sequences from two spatially different transmitting positions by a transmitter diversity system, by modulating each of the preambles C_n ^A and C_n ^B by an OFDM system, using two symbol sequences C_n ^A and C_n ^B comprising M sub-carriers that form a regular matrix [c_n ^A , C_n ^B ] ^τ as preambles ; an initial transfer function estimating step of estimating an initial transfer function H by demodulating a receive signal obtained by receiving signals transmitted by the preamble transmitting step at one receiving position by applying discrete Fourier transform thereto, thereby generating a receive symbol sequence R^c _n comprising M sub-carriers, and using the receive symbol sequence R^c _n for an inverse matrix of a matrix (C_n ^A , C_n ^B ) ^τ constituted of the known symbol sequences C_nA and C_nB, thereby obtaining 'the transfer function; and a hard decision step of performing hard decision for obtaining hard decision values X_n, " , X_n+ι" of the symbol sequences Xi _r Xn₊i' from the symbol sequences X_n' , X_n+ι' demodulated by the STBC demodulating step by using the transfer function matrix H, based on receive symbol sequences R_n, R_n+ι generated by demodulating the receive signal obtained by receiving the transmission signal of the symbol sequences X_n, X_n+ι of two blocks, to which space time block coding is applied, and which is subsequently transmitted by the OFDM demodulating step; and a transfer function updating step of updating the transfer function for estimating a new transfer function matrix H from hard decision values X_n", Xn₊i" of symbol sequences X_n' , X_n+ι' and the receive symbol sequences R_n, R_n+ι-

6. A communication method, comprising: an STBC processing step of performing STBC-processing for generating a symbol sequence X_k (k=0, ..., M-l) of sub-carriers of M-columns by dividing a transmit symbol sequence X into blocks comprising M (M≥2) sub-carriers so as to be made parallel per block unit, and generating two mutually orthogonal symbol sequences X_kA, X_kB, based on the symbol sequence X_k of each sub-carrier; a transmitting step of transmitting symbol sequences from two spatially different transmitting positions by a transmitter diversity system, by demodulating a combination of the symbol sequences {XA} and {X_kB} for each block by an OFDM system; ' an OFDM demodulating step of demodulating OFDM-processed codes for generating a receive symbol sequence R_k (k=0, ..., M-l) of the sub-carriers of M-columns, by applying discrete Fourier transform to a receive signal obtained by receiving signals transmitted by the transmitting step at one receiving position; and an STBC demodulating step of demodulating STBC-processed codes for demodulating a symbol sequence X_k' of each sub-carrier by using the receive symbol sequence R_k for inverse matrix H^"1 of transfer function matrix H, which is constituted based on a transfer function estimated for each block and for each sub-carrier by a prescribed estimation method, and by which the receive symbol sequence R_k is related to the symbol sequence X .

7. The communication method according to claim 6, comprising: a preamble transmitting step of transmitting preambles for transmitting preambles by a transmitter diversity system from two spatially different transmitting positions by modulating each combination of preambles {C_k ^A}, {C_k ^B} for each block by an OFDM system, using the symbol sequences C_k ^A, C_k ^B (k=0,l,.... M-l) of the sub-carriers of M-columns that form a regular matrix of [c_k ^A , C_k ^B ] ^τ as preambles; an initial transfer function estimating step of estimating an initial transfer function matrix for estimating an initial transfer function matrix H by demodulating the receive signal obtained by receiving the signal transmitted by the transmitting step at one receiving position, by applying discrete Fourier transform thereto, to generate the receive symbol sequence R% of the sub-carriers of M-columns, and using the receive symbol sequence R^c _k for the inverse matrix of the matrix (C_k ^A , C_k ^B )^τ constituted of the known symbol sequences C_kA and C_kB, thereby obtaining the transfer function; a hard decision step of performing hard decision for obtaining hard decision values "X_k, X_k+ι" of the symbol sequences X' , X_k+ι' from the symbol sequences X_k' , X_k+ι' demodulated by using the transfer function matrix H in the STBC demodulating step, based on the receive symbol sequences R_k, R_k+ι generated by demodulating the receive signal obtained by receiving the transmission signal of the symbol sequences X_k, X_k+ι of the sub-carriers of two-columns, to which space time block coding is applied, and which is subsequently transmitted in the OFDM demodulation step; and a transfer function updating step updating the transfer function for estimating a new transfer function matrix H from hard decision values X", X_k+ι" and receive symbol sequences R, R_k+ι.

A communication system, comprising: a transmitter comprising an BC encoder for dividing an inputted transmit symbol sequence into blocks comprising a prescribed number of symbols, and encoding the symbol sequence thus divided by a space-time block coding (referred to as "STBC" hereafter) or space frequency block coding (referred to as "SFBC" hereafter) for each block; a diversity transmitter for conducting wireless transmission of STBC-processed codes or SFBC-processed codes of n_τ sequerfces outputted by a BC encoder from n_τ (n_τ≥2) transmitting antennas by a transmitter diversity system; and a receiver for demodulating the transmit symbol sequence, based on a receive symbol sequence obtained by receiving wireless signals transmitted from each transmitting antenna by n_R (n_R≥l) receiving antennas, the receiver further comprising: a transfer function storage part for storing the value of the transfer function of a channel between each transmitting antenna and each receiving antenna; the BC decoder for estimating the transmit symbol sequence by decoding STBC-processed codes or decoding SFBC-processed codes by hard decision, based on the value of each transfer function stored in the transfer function storage part and a receive symbol; a transfer function computer for estimating the value of the transfer function of e'ach channel, by dividing a vector (receive symbol vector) whose element is the receive symbol per unit block, by a vector (transmit symbol vector) whose element is the transmit symbol sequence per unit block estimated by the BC encoder; and a transfer function updating part for updating the value of the transfer function stored in the transfer function storage part, to the value of the transfer function estimated by the transfer function computer, every time that the value of the transfer function is estimated by the transfer function computer.

9. The communication system according to claim 8, comprising: a transmitter comprising: a flame dividing part for dividing the transmit symbol sequence to be transmitted to the receiver into data flames comprising a prescribed number of blocks; a preamble generator for generating a preamble comprising a symbol sequence of known pattern (referred to as "training sequence" hereafter) ; and a preamble inserting part for inputting the preamble and the data flame in the BC encoder alternatively as the transmit symbol sequence, and a receiver comprising a transfer function estimating part for estimating the value of the transfer function of each channel by dividing a vector whose element is the receive symbol of the preamble, by a vector whose element is a training sequence of known pattern, and storing the value of the transfer function in the transfer function storage part, wherein the transfer function computer and the transfer function updating part estimate the value of the transfer function of each channel, and update the value of the transfer function stored in the transfer function storage part, respectively when the data flame is received.

10. The communication system according to any one of claim 8 or claim 9, comprising: a transmitter comprising an OFDM modulator for modulating

STBC-processed codes or SFBC-processed codes of n_τ sequences outputted by the BC encoder by an orthogonal frequency division multiplex (referred to as "OFDM" hereafter) system, thefeby generating OFDM symbols, wherein the diversity transmitting part functions to conduct wireless transmission of the OFDM symbol sequence of n_τ-column modulated by the OFDM modulator, fromn_τ (n_τ≥2) transmitting antennas by a transmitter diversity system, and a receiver comprising: a receiving part for receiving wireless signals which are transmitted from each transmitting antenna by n_R (n_R≥l) receiving antennas; and an OFDM demodulator for demodulating the receive signal received by the receiving part by the OFDM system, thereby generating the receive symbol sequence.

11. A communication system, comprising: an STBC encoder for generating two mutually orthogonal symbol sequences X_n ^A, X_n ^B comprising M sub-carriers by dividing the symbol sequence X to be transmitted into blocks comprising M (M≥2) sub-carriers, based on the symbol sequence X_n (n=0, 1, 2, ...; n is a block number) of each block; a transmitting part for modulating each of the symbol sequences X_n ^A, X_n ^B by the OFDM system, and transmitting the symbol sequence thus demodulated from two spatially different transmitting positions by a transmitter diversity system; an OFDM demodulator for demodulating the receive signal obtained by receiving the signal transmitted by the transmitter at one receiving position, by applying discrete Fourier transform thereto, and generating the receive symbol sequence R_n comprising

M sub-carriers; and an STBC demodulator for demodulating the symbol sequence X_n of each block by using the receive symbol sequence R_n for inverse matrix H^"1 of transfer function matrix H, which is constituted based on the transfer function estimated for each block and for each sub-carrier by a prescribed estimation method, and by which the receive symbol sequence R_n is related to the symbol sequence X_n.

12. The communication system according to claim 11, comprising: a preamble transmitting part for demodulating by an OFDM system each of the two symbol sequences C_n, C_n ^B comprising M sub-carriers that form a regular matrix [c_n ^A, C_n ^B] ^τ by using such two symbol sequences as preambles, and transmitting the symbol sequence thus demodulated from two spatially different transmitting positions by a transmitter diversity system; an initial transfer function estimation part for estimating an initial transfer function matrix H by applying the discrete Fourier transform to a receive signal obtained by receiving the signals transmitted by the preamble transmitting part at one receiving position, demodulating it and generating a receive symbol sequence R^c _n comprising M sub-carriers^', and obtaining the transfer function by operating the inverse matrix of the matrix (C_n ^A, C_n ^B)^T constituted of the known symbol sequences C_n ^A , C_n ^B,to the receive symbol sequence R^c _n ; and a hard decision unit for demodulating the receive signal obtained by receiving the transmission signal of symbol sequences X_nr Xn₊i of two blocks, to which space time block coding is applied, and which is subsequently transmitted from the transmitter, by the OFDM demodulator, and thereby generating receive symbol sequences _nf Rn₊i_r and based on the receive symbol sequences R_n, R_n+i_r obtaining hard decision values "X_n, X_n+ι" of symbol sequences X_n' , X_n+ι' from symbol sequences X_n' , X_n+ι' demodulated by the STBC demodulator using the transfer function matrix H; and a transfer function updating part for estimating a new initial transfer function matrix H, from the hard decision values X_n, " , X_n+ι" and the receive symbol sequences R_n, R_n+ι-

13. A communication system, comprising: an STBC encoder for generating a symbol sequence X_k (k=0, ..., M-l) of sub-carriers of M-columns by dividing a transmitting symbol sequence X into blocks comprising M (M≥2) sub-carriers, and making them parallel per block unit, and generating two mutually orthogonal symbol sequences X_k ^Aand X_k ^B, based on the symbol sequence X_k of each sub-carrier; a transmitting part for modulating the combination of the symbol sequences {X_k ^A} and {X_k ^B} for each block by an OFDM system and transmitting the symbol sequence thus demodulated from two spatially different transmitting positions by a transmitter diversity system; an OFDM demodulator for demodulating the receive signal obtained by receiving the signal transmitted by the transmitter at one receiving position by applying discrete Fourier transform thereto, and generating a receive symbol sequence R_k (k=0, ..., M-l) of sub-carriers of M-columns; and an STBC demodulator for demodulating a symbol sequence X_k' of each sub-carrier by operating the inverse matrix H^" of transfer function matrix H, which is constituted based on a transfer function estimated for each block and for each sub-carrier by a prescribed estimation method and by which the receive symbol sequence R_k is related to the symbol sequence X_k.,to the receive symbol sequence

Rk • 14. The communication system according to claim 13, comprising: a preamble transmitting part for modulating each combination of the preambles {C_k ^A} and {C_k ^B} for each block, using the symbol sequences C_k ^A, C_k ^B (k=0,l,..., M-l) of the sub-carriers of M-columns that form a regular matrix [c^A , C_k ^B ] ^τ as preambles by an OFDM system, and transmitting the symbol sequences thus modulated from two spatially different transmitting positions by a transmitter diversity system; a transfer function estimating part for estimating an initial transfer function matrix H, by applying discrete Fourier transform to the receive signal obtained by receiving the signal transmitted by the transmitting part at one receiving position, thereby demodulating the signal thus received, and generating the receive symbol sequence R^c _k of the sub-carriers of M-columns, and operating the inverse matrix of the matrix [c_k ^A , C_k ^B ] ^τ constituted of the known symbol sequences C_kA and C_kB,to the receive symbol sequence R^c _k , , thereby obtaining the transfer function; and a hard decision unit for demodulating the receive signal obtained by receiving the transmission signal of the symbol sequences X_k, X_k+ι of sub-carriers of two-columns to which space time block coding is applied, and which is subsequently transmitted from the transmitter, by the OFDM demodulator, and thereby generating receive symbol sequences R_k, R₊ι, and based on the receive symbol sequences R, R_k+ι, obtaining hard decision values X_k, " , X_k+ι" of the symbol sequences X_k' , X_k+ι' from the symbol sequences X_k' , X_k+ι' demodulated by using the transfer function matrix H by the STBC demodulating part; and a transfer function updating part fpr estimating a new transfer function matrix H from the hard decision values X_k", X_k+ι" and the receive symbol sequences R_k, R_k+ι.

15. A receiver for demodulating the transmit symbol sequence based on a receive symbol sequence obtained by receiving a wireless signal by n_R (n_R≥l) receiving antennas, the wireless signal being transmitted by a transmitter diversity system from n_τ (n_τ≥2) transmitting antennas after the transmit symbol sequence divided into blocks comprising a prescribed number of symbols is encoded by a space-time block coding (referred to as "STBC" hereafter) or space frequency block coding (referred to as "SFBC" hereafter) for each block, the receiver comprising: a transfer function storage part for storing the value of the transfer function of a channel between each transmitting antenna and each receiving antenna; a BC decoder for estimating a transmit symbol sequence by decoding STBC-processed codes or SFBC-processed codes by Hard decision, based on the value of each transfer function stored in the transfer function storage part and each of the receive symbols; a transfer function computer for estimating the value of the transfer function of each channel, by dividing a vector whose element is a receive symbol per unit block, by a vector whose element is a transmit symbol sequence per unit block estimated by the BCdecoder; and a transfer function updating part for updating the value of the transfer function stored in the transfer function storage part to the value of the transfer function estimated by the transfer function computer every time that the value of the transfer function is estimated by the transfer function computer.

16. The receiver according to claim 15, comprising: a receiving part for receiving the wireless signal transmitted from each transmitting antenna by n_R (n_R≥l) receiving antennas, wherein the receive symbol sequence is modulated by an OFDM system; and an OFDM demodulator for generating the receive symbol sequence by demodulating the receive signal received by the reception part by the OFDM system.

17. A receiver for receiving a signal transmitted from a transmitter, comprising: the transmitter comprising: an STBC encoder for dividing the transmitting symbol sequence X into blocks comprising M (M≥2) sub-carriers, and generating two mutually orthogonal symbol sequences X_n ^A and X_n ^B comprising M sub-carriers based on a symbol sequence X_n (n=0, 1, 2,...; n is a block number) of each block; and a transmitting part for modulating each of the symbol sequences X_n ^A and X_n ^B by an OFDM system, and transmitting the symbol sequence thus modulated from two spatially different transmitting 5 positions by a transmitter diversity system, and wherein the receiver for receiving the signal transmitted from the transmitter thus constructed and demodulating the symbol sequence X thus transmitted, comprising: an OFDM demodulator for generating a receive symbol sequence0 R_n comprising M sub-carriers by applying discrete Fourier transform to a receive signal obtained by receiving signals transmitted by the transmitting part at one receiving position, thereby demodulating receive signals; and an STBC demodulator for demodulating a symbol sequence X_n'5 of each block by operating the inverse matrix H^_1 of transfer function matrix H, which is constituted based,, on the transfer function estimated for each block and for each sub-carrier by a prescribed estimation method, and by which the receive symbol sequence R_n is related to the- symbol sequence X_n,to the receive symbol sequence U R_n . n•

18. The receiver according to claim 17, comprising: the said transmitter comprising a preamble transmitting part for modulating each combination of preambles {C_n ^A}, {C_π ^B} by an OFDM5 system, using two symbol sequences C_n, C_n ^B comprising M sub-carriers that form a regular matrix of [C_n ^A , C_n ^B ] ^τ as preambles, and transmitting the preambles thus modulated from two spatially different transmitting positions by a transmitter diversity system and wherein the receiver comprising: a transfer function estimating part for estimating an initial transfer function matrix H, by applying discrete Fourier transform to the receive signal obtained by receiving the signal transmitted by the preamble transmitting part at one receiving position, thereby demodulating the signal thus received, and generating the receive symbol sequence R^c _n comprising M sub-carriers, and operating the inverse matrix of the matrix (C_n ^A , Cn_n ^B ) ^τ constituted of the known symbol sequences C_nA and C_nB, to the receive symbol sequence R^c _n , thereby obtaining the transfer function; a hard decision unit for demodulating the receive signal obtained by receiving the transmission signal of symbol sequences X_n, X_n+i of two blocks, to which space time block coding is applied, and which is subsequently transmitted from the transmitter, by the OFDM demodulator, thereby generating receive symbol sequences R_n, R_n+i_r and based on the receive symbol sequences R_n, R_n+ι, obtaining hard decision values "X_n, X_n+ι" of the symbol sequences X_n' , X_n+ι' from symbol sequences X_n' , X_n+ι' demodulated by the STBC demodulator using the transfer function matrix H; and transfer function updating part for estimating a new transfer function matrix H from hard decision values X_n", X_n+ι" and receive symbol sequences R_n, R_n+ι-

19. A receiver comprising: a transmitter comprising: an STBC encoder for generating a symbol sequence X_k (k=0, ..., M-l) of the sub-carriers of M-columns by dividing a transmitting symbol sequence X into blocks comprising M (M≥2) sub-carriers so as to be made parallel per block unit, and generating two mutually orthogonal symbol sequences X_k ^A and X_k , based on a symbol sequence X of each sub-carrier; and a transmitting part for demodulating combination of symbol sequences {X_k ^A} and {X_k ^B} for each block by an OFDM system and transmitting the symbol sequence thus demodulated from two spatially different transmitting positions by a transmitter diversity system, and wherein the receiver for receiving the signal transmitted by the transmitter thus constructed and demodulating the symbol sequence X thus transmitted, comprising: an OFDM demodulator for demodulating receive signals obtained by receiving signals transmitted by the transmitter at one receiving position by applying discrete Fourier transform thereto, and generating a receive symbol sequence R_k (k=0, ..., M-l) of sub-carriers of M-columns; and an STBC demodulator for demodulating the symbol sequence X_k ^' of each sub-carrier by operating an inverse matrix H^_1 of transfer function a matrix H, constituted based on a transfer function estimated for each block and for each sub-carrier by a prescribed estimation method, by which a receive symbol sequence R is related to the symbol sequence X,to the receive symbol sequence R_k ,

20. The receiver according to claim 19, comprising: the said transmitter comprising a preamble transmitting part for modulating each combination of preambles {C_k ^A}, {C_k ^B} for each block by an OFDM system, using the symbol sequences C_k ^A, C_k ^B (k=0,

..., M-l) comprising sub-carriers of M-columns that form a regular matrix of (C_k ^A , C_k ^B ] ^τ as preambles, and transmitting the preambles thus modulated from two spatially different transmitting positions by a transmitter diversity system, and wherein the receiver comprising: a transfer function estimating part for estimating an initial transfer function matrix H, by applying discrete Fourier transform to the receive signal obtained by receiving- signals transmitted by the preamble transmitting part at one receiving position, thereby demodulating the signals thus received, and generating a receive symbol sequence R^c _n comprising M sub-carriers, and operating the inverse matrix of the matrix (C_n ^A , Cn_n ^B )^τ constituted of the known symbol sequences C_n ^A and C_n ^B,to receive symbol sequence R^c _n , thereby obtaining the transfer function; a hard decision unit for demodulating the receive signal obtained by receiving transmission signals of the symbol sequences X_k, X_k+ι of sub-carriers of two-columns to which space time block coding is applied, and which is subsequently transmitted from the transmitting part, by the OFDM demodulator, and thereby generating receive symbol sequences R._k, R_k+ι, and based on the receive symbol sequences R_k, R_k+ι, obtaining hard decision values "X_k, X₊ι" of the symbol sequences X_k' , X₊ι' from the symbol sequences X_k' , X_k+ι' demodulated by the STBC demodulator using a transfer f nction matrix H; and a transfer function updating part for estimating a new transfer function matrix H from the hard decision values X", X+ι" and the receive symbol sequences R_k, R_k+ι.