Transmitter and method for transmitting symbol

Abstract

The invention relates to transmitting symbols in a MIMO wireless communication system, said method comprising: determining a p value; applying to a first block of M data symbols X=(X.sub.0, . . . X.sub.M-1) a pre-coder to obtain a second block of M symbols Y=(Y.sub.0, . . . Y.sub.M-1) with Formula (I); applying a M size DFT then a N size IDFT to the first block of M symbols to obtain a first SC-FDMA symbol, said first SC-FDMA symbol being of a given duration; applying a M size DFT then a N size IDFT to the second block of M symbols to obtain a second SC-FDMA symbol, said second SC-FDMA symbol being of the given duration; transmitting during a time interval of the given duration, simultaneously the first and second SC-FDMA symbols, into the radio signal.

Claims

1. A method for transmitting symbols through a radio signal in a wireless communication system, said radio signal being emitted by a transmitter comprising at least two transmit antennas, each antenna being configured for transmitting on at least an even number M, strictly greater than 1, of different frequencies, said method comprising: applying to a first block of M symbols X=(X.sub.0, . . . X.sub.M-1) a pre-coder to obtain a second block of M symbols Y=(Y.sub.0, . . . Y.sub.M-1), with $Y_k=\{\begin{array}{c}\mathrm{.Math.}{X}_{\frac{M}{2}+P_1+\mathrm{mod}\left(-k+P_1+p-1,Q\right)}^{*},\mathrm{for}k\in 〚P_1;\frac{M}{2}-P_2〛\\ -\mathrm{.Math.}{X}_{P_1+\mathrm{mod}\left(-k+P_1+\frac{M}{2}+p-1,Q\right)}^{*},\mathrm{for}k\in 〚\frac{M}{2}+P_1;M-P_2〛\end{array},$ with P.sub.1 and P2 predefined integers, positive or equal to 0, such as P.sub.1+P.sub.2 is strictly smaller than M/2, p a predetermined integer Q is an integer, and ε is 1 or −1 and X.sub.k* being the complex conjugate of X.sub.k; applying at least an M size DFT then an N size IDFT corresponding to a first transmit antenna, to the first block of M symbols to obtain a first single-carrier frequency division multiple access, SC-FDMA, symbol representing the first block of M symbols, said first SC-FDMA symbol being of a given duration; applying at least a M size DFT then a N size IDFT corresponding to a second transmit antenna, to the second block of M symbols to obtain a second single-carrier frequency division multiple access, SC-FDMA, symbol representing the second block of M symbols, said second SC-FDMA symbol being of the given duration; transmitting during a time interval of the given duration, respectively on the first and second transmit antennas, simultaneously the first and second SC-FDMA symbols, into the radio signal.

2. The method according to claim 1, wherein mod (p, Q)≠1, with Q=M/2−(P1+P2).

3. The method according to claim 1, wherein $\mathrm{mod}\left(p,Q\right)\in 〚\frac{Q}{4};\frac{3.Q}{4}〛$ with Q=M/2−(P1+P2).

4. The method according to claim 3, wherein mod(p, Q) is equal to ┌Q/2┐ and/or └Q/2┘.

5. The method according to claim 1, wherein mod(p, Q)=K, where K is a number of symbols in a group of symbols comprising symbols from the P.sub.1-th symbol X.sub.P.sub.1 of the first block of M symbols to the (P.sub.1+K)-th symbol X.sub.P.sub.1.sub.+K of the first block of M symbols.

6. The method according to claim 5, wherein the symbols of the group of symbols are reference signal symbols and/or control symbols.

7. The method according to claim 1, wherein mod(p, Q)=0, with Q=M/2−(P1+P2).

8. The method according to claim 7, wherein L first groups G.sub.i of respectively K.sub.i symbols of the first block of M symbols, with Σ.sub.j=1.sup.L K.sub.j equal to Q are defined and for each i: the K.sub.i symbols of the i-th first group G.sub.i being the symbols from the (P.sub.1+Σ.sub.j=1.sup.i-1K.sub.j)-th symbol $X_{P_1+\underset{j=1}{\overset{i-1}{.Math.}}{K}_j}$ to the (P.sub.1+Σ.sub.j=1.sup.iK.sub.j−1)-th symbol $X_{P_1+\underset{j=1}{\overset{i}{.Math.}}{K}_j-1}$ of the first block of M symbols are of the same i-th type as K.sub.i symbols of a second group G′.sub.i of K.sub.i symbols of the first block of M symbols, the K.sub.i symbols of the second group G′.sub.i being the symbols from the (M−P.sub.2−Σ.sub.j=1.sup.iK.sub.j)-th symbol $X_{M-P_2-\underset{j=1}{\overset{i}{.Math.}}{K}_j}$ to the (M−P.sub.2−Σ.sub.j=1.sup.i-1K.sub.j−1)-th symbol $X_{M-P_2-\underset{j=1}{\overset{i-1}{.Math.}}{K}_j-1}$ of the first mock of M symbols.

9. The method according to claim 8, wherein for each i, the i-th type of symbol is one among data symbol, reference signal symbol or control symbol.

10. The method according to claim 9, wherein for each i, the symbols of the i-th group G.sub.i are of different type of symbol than the symbols of the i+1-th group G.sub.i+1.

11. The method according to claim 1, wherein determining the p value is based at least on one among: a cell specific p value information; a set of predetermined values; a dynamic control indication; a reference signal, RS, configuration; a Modulation and Coding Scheme, MCS; a user-specific parameter; a size of a resource allocation allocated to the transmitter; a transmitter specific p value information; another transmitter's p′ value such as the another transmitter applies to a first block of M′ symbols X=(X.sub.0, . . . X.sub.M′-1) a pre-coder to obtain a second block of M′ symbols Y=(Y.sub.0, . . . Y.sub.M′-1), with $Y_k=\{\begin{array}{c}\mathrm{.Math.}{X}_{\frac{M\prime }{2}+P_1^{\prime }+\mathrm{mod}\left(-k+P_1^{\prime }+p\prime -1,Q\right)}^{*},\mathrm{for}k\in 〚P_1^{\prime };\frac{M\prime }{2}-P_2^{\prime }〛\\ -\mathrm{.Math.}{X}_{P_1^{\prime }+\mathrm{mod}\left(-k+P_1^{\prime }+\frac{M}{2}+p\prime -1,Q\right)}^{*},\mathrm{for}k\in 〚\frac{M\prime }{2}+P_1^{\prime };M-P_2^{\prime }〛\end{array},$ with P′.sub.1 and P′.sub.2 predefined integers, positive or equal to 0, such as P′.sub.1+P′.sub.2 is strictly smaller than M′/2 and ε is 1 or −1.

12. The method according to claim 1, wherein the p value is determined randomly among a set of predetermined values.

13. The method according to claim 1, wherein a value of a n-th symbol X.sub.n of the first block of M symbols: is equal to a value of a (n+Q)-th symbol X.sub.n+Q of the first block of M symbols if n∈ 0;P.sub.1−1∪M/2;M/2+P.sub.1−1; is equal to a value of a (n−Q)-th symbol X.sub.n−Q of the first block of M symbols if n∈ $〚\frac{M}{2}-P_2;\frac{M}{2}-1〛.Math.〚M-P_2;M-1〛.$

14. A non-transitory computer readable medium storing a program comprising code instructions to perform the method according to claim 1, when said instructions are run by at least a processor.

15. Transmitter for transmitting symbols through a radio signal in wireless communication system, said transmitter comprising: at least two transmit antennas, each antenna being configured for transmitting on at least an even number M, strictly greater than 1, of different frequencies, a processor; and a non-transitory computer-readable medium comprising instructions stored thereon, which when executed by the processor configure the transmitter to: apply to a first block of M symbols X=(X.sub.0, . . . X.sub.M-1) a precoder to obtain a second block of M symbols Y=(Y.sub.0, . . . Y.sub.M-1), with $Y_k=\{\begin{array}{c}\mathrm{.Math.}{X}_{\frac{M}{2}+P_1+\mathrm{mod}\left(-k+P_1+p-1,Q\right)}^{*},\mathrm{for}k\in 〚P_1;\frac{M}{2}-P_2〛\\ -\mathrm{.Math.}{X}_{P_1+\mathrm{mod}\left(-k+P_1+\frac{M}{2}+p-1,Q\right)}^{*},\mathrm{for}k\in 〚\frac{M}{2}+P_1;M-P_2〛\end{array},$ with P.sub.1 and P.sub.2 predefined integers, positive or equal to 0, such as P.sub.1+P.sub.2 is strictly smaller than M/2, p a predetermined integer Q is an integer, and ε is 1 or −1 and X.sub.k* being the complex conjugate of X.sub.k; apply at least an M size DFT then an N size IDFT corresponding to a first transmit antenna, to the first block of M symbols to obtain a first single-carrier frequency division multiple access, SC-FDMA, symbol representing the first block of M symbols, said first SC-FDMA symbol being of a given duration; apply at least a M size DFT then a N size IDFT corresponding to a second transmit antenna, to the second block of M symbols to obtain a second single-carrier frequency division multiple access, SC-FDMA, symbol representing the second block of M symbols, said second SC-FDMA symbol being of the given duration; transmit during a time interval of the given duration, respectively on the first and second transmit antennas, simultaneously the first and second SC-FDMA symbols, into the radio signal.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 illustrates a specific SS-STBC like transmitter and receiver.

(2) FIG. 2 schematizes a block diagram of a specific SS-STBC like transmitter according to the invention.

(3) FIG. 3 details the specific SS-STBC like pre-coder logical functioning according to the invention.

(4) FIG. 4 details the specific SS-STBC like pre-coder logical functioning according to the invention.

(5) FIG. 5 details the specific SS-STBC like pre-coder logical functioning with the p value set to ┌Q/2┐ and/or └Q/2┘ according to the invention.

(6) FIG. 6 details the specific SS-STBC like pre-coder logical functioning with the p value set to K according to the invention.

(7) FIG. 7 details the specific SS-STBC like pre-coder logical functioning with the p value set to 0 according to the invention.

(8) FIG. 8 illustrates a flowchart representing the steps for transmitting symbols in the radio signal according to the invention.

DESCRIPTION OF EMBODIMENTS

(9) Referring to FIG. 1, there is shown a transmitter 1.1 transmitting a radio signal to a receiver 1.2. The transmitter 1.1 is in the cell of the receiver 1.2. This transmission may be a specific SS-STBC based transmission in the context of OFDM based system. In this example the transmitter 1.1 is a mobile terminal (also called user equipment, UE) and the receiver 1.2 is a fixed station which in the context of LTE is a base station. The transmitter 1.1 can as well be the fixed station and the receiver 1.2 a mobile terminal. It is also possible to have both the transmitter 1.1 and the receiver 1.2 as mobile terminals (for example during device-to-device or sidelink communication).

(10) The transmitter 1.1 comprises one communication module (COM_trans) 1.3, one processing module (PROC_trans) 1.4 and a memory unit (MEMO_trans) 1.5. The MEMO_trans 1.5 comprises a non-volatile unit which retrieves the computer program and a volatile unit which retrieves the parameters used for the communication, like the p value used for pre-coding. The PROC_trans 1.4 is configured to pre-code the first block of M symbols X into the second block of M symbols Y according to the specific SS-STBC like pre-coder. The COM_trans is configured to transmit to the receiver 1.2 the radio signal. The processing module 1.4 and the memory unit 1.5 can be dedicated to the pre-coding or also used for other functions of the transmitter like for the other steps of the processing of the radio signal.

(11) The receiver 1.2 comprises one communication module (COM_recei) 1.6, one processing module (PROC_recei) 1.7 and a memory unit (MEMO_recei) 1.8. The MEMO_recei 1.8 comprises a non-volatile unit which retrieves the computer program and a volatile unit which retrieves the parameters used for the communication, like the p value used for pre-coding. The PROC_recei 1.7 is configured to de-code the signal to retrieve the symbols of the first block of M symbols X. The COM_recei 1.6 is configured to receive from the transmitter the radio signal.

(12) Referring to FIG. 2, there is shown a block diagram of a specific SS-STBC like transmitter. Such specific SS-STBC like transmitters apply SC-FDMA schemes on a block of symbols (first block of symbols) and a pre-coded block of symbols (second block of symbols) to obtain the radio signal. This ensures full diversity for a rate of one symbol per channel use. Such transmitter emits a radio signal by emitting on at least two transmit antennas Tx1 2.0 and Tx2 2.1.

(13) The radio signal being provided by applying a specific SS-STBC like pre-coder 2.2 to a first block of symbols X=(X.sub.0, . . . X.sub.M-1) and obtaining a second block of symbols Y=(Y.sub.0, . . . Y.sub.M-1). The first block of symbols may be obtained by a QPSK digital modulation scheme or any other digital modulation scheme as QAM. M is the number of allocated subcarriers. In such SS-STBC scheme, M is even.

(14) Then, a M-size DFT 2.3, 2.4 (discrete Fourier transform) is applied to each block of symbols X and Y. For each block of symbols, M complex symbols are obtained in the frequency domain, which are respectively

(15) ${\left(S_k^{\mathrm{Tx}1}\right)}_{k\in 〚0;M-1〛}\mathrm{and}{\left(S_k^{\mathrm{Tx}2}\right)}_{k\in 〚0;M-1〛}.$
That is, for each M-size DFT 2.3, 2.4, one complex symbol is obtained for each k-th subcarrier among the M allocated subcarriers. These complex symbols are mapped with subcarrier mapping modules 2.5 and 2.6 in the frequency domain to M out of N inputs of N-size IDFT modules, 2.7, 2.8. Regarding the subcarrier mapping, each vector of complex symbols

(16) $S^{\mathrm{Tx}1}={\left(S_k^{\mathrm{Tx}1}\right)}_{k\in 〚0;M-1〛}\mathrm{and}{S}^{\mathrm{Tx}2}={\left(S_k^{\mathrm{Tx}2}\right)}_{k\in 〚0;M-1〛}$
is mapped to the M allocated subcarriers out of N existing subcarriers via subcarrier mapping modules 2.5 and 2.6. The subcarrier mapping can be for example localized, that is the M elements of each vector S.sup.Tx1,2 are mapped to M consecutive subcarriers among the N existing. The subcarrier mapping can be for example distributed, that is the M elements of each vector S.sup.Tx1,2 are mapped equally distanced over the entire bandwidth with zero occupying the unused subcarriers.

(17) Inverse DFT of size N 2.7 and 2.8 are then applied to the two resulting vectors {tilde over (S)}.sup.Tx1 and {tilde over (S)}.sup.Tx2 of the subcarrier mapping modules 2.5 and 2.6, therefore generating two SC-FDMA symbols, each of them being sent at the same time from respectively one of the two transmit antennas. More precisely, at the output of the IDFT modules, 2.7, 2.8 a signal {tilde over (x)}.sup.Tx1=({tilde over (x)}.sup.Tx1.sub.0, . . . , {tilde over (x)}.sup.Tx1.sub.N-1) and a signal {tilde over (x)}.sup.Tx2=({tilde over (x)}.sup.Tx2.sub.0, . . . , {tilde over (x)}.sup.Tx2.sub.N-1) are obtained. Each of these signals occupy during a time interval corresponding to a single-carrier frequency division multiple access, SC-FDMA, symbol, M allocated subcarriers out of the N existing subcarriers. The signals {tilde over (x)}.sup.Tx1 and {tilde over (x)}.sup.Tx2 are time-domain signals whose frequency-domain representations, during a given time interval, are respectively the complex symbols S.sub.k.sup.Tx1 and S.sub.k.sup.Tx2 for each k.sup.th occupied subcarrier with k=0 to M−1. Equivalently, the time-domain signals {tilde over (x)}.sup.Tx1 and {tilde over (x)}.sup.Tx2 during a given time interval represent respectively, in the frequency domain, the complex symbols S.sub.k.sup.Tx1 and S.sub.k.sup.Tx2 for each k.sup.th frequency with k=0 to M−1. These time-domains signals {tilde over (x)}.sup.Tx1 and {tilde over (x)}.sup.Tx2 respectively correspond to SC-FDMA symbols. Therefore, samples in the signal {tilde over (x)}.sup.Tx1 or in the signal {tilde over (x)}.sup.Tx2 refer respectively to samples in a SC-FDMA symbol corresponding to a first transmit antenna 2.0 and to samples in a SC-FDMA symbol corresponding to a second transmit antenna 2.1.

(18) A cyclic prefix can be optionally appended after IDFT.

(19) Referring to FIG. 3 there is shown in detail the logical functioning of the specific SS-STBC like pre-coder module 2.2.

(20) The SS-STBC like pre-coder 2.2 applied to the block of symbols X=(X.sub.0, . . . X.sub.M-1) (also referred as the first block of symbols) outputs the block of symbols Y=(Y.sub.0, . . . Y.sub.M-1) (also referred as the second block of symbols). Considering the first block of symbols X=(X.sub.0, . . . X.sub.M-1) this one is divided in two parts of M/2 symbols as showed on FIG. 2.2. The first, respectively the second part, contains Q contiguous modulation symbols , respectively contiguous symbols . The Q contiguous modulation symbols of the first part and the second part may contain data, control information and reference signals.

(21) To limit the interference between the two parts of the block of symbols, the first part may contain a cyclic prefix of P.sub.1 contiguous symbols and/or a cyclic postfix of P.sub.2 contiguous symbols respectively positioned before and after the Q contiguous modulation symbols . The second part may also contain a cyclic prefix of P.sub.1 contiguous symbols and/or a cyclic postfix of P.sub.2 contiguous symbols respectively positioned before and after the Q contiguous modulation symbols . P1 and/or P2 values may also be set to 0, and in that case no prefix and/or no postfix is included.

(22) Therefore, the first block of symbols X=(X.sub.0, . . . X.sub.M-1) can be defined:

(23) X.sub.0=A.sub.Q-P.sub.1, . . . , X.sub.P.sub.1.sub.−1=A.sub.Q-1, for the cyclic prefix of the first part,

(24) X.sub.P.sub.1=A.sub.0, X.sub.P.sub.1.sub.+1=A.sub.1, . . . , X.sub.P.sub.1.sub.+Q-1=A.sub.Q-1, for the useful symbols (data, RS, control symbols) of the first part,

(25) $X_{P_1+Q}=A_0,\mathrm{.Math.},X_{\frac{M}{2}-1}=A_{P_2-1},$
for the cyclic postfix of the first part,
X.sub.M/2=B.sub.Q-P.sub.1, . . . , X.sub.M/2±P.sub.1.sub.−1=B.sub.Q-1, for the cyclic prefix of the second part,
X.sub.P.sub.1.sub.+M/2=B.sub.0, X.sub.P.sub.1.sub.+M/2+1=B.sub.2, . . . , X.sub.M-P.sub.2.sub.−1=B.sub.Q-1, for the useful symbols (data, RS, control symbols) of the second part,
X.sub.M-P.sub.2=B.sub.0, . . . , X.sub.M-1=B.sub.P.sub.2.sub.−1, for the cyclic postfix of the second part.

(26) When applying the specific SS-STBC like pre-coder to the first block of symbols X=(X.sub.0, X.sub.M-1), the second block of symbols Y=(Y.sub.0, . . . Y.sub.M-1) is obtained. This second block of symbols can be defined relatively to the first block of symbols previously defined, as:

(27) Y.sub.0={tilde over (B)}.sub.Q-P.sub.1, . . . , Y.sub.P.sub.1.sub.−1={tilde over (B)}.sub.Q-1, for the cyclic prefix of the first part,

(28) Y.sub.P.sub.1={tilde over (B)}.sub.0, Y.sub.P.sub.1.sub.+1={tilde over (B)}.sub.1, . . . , Y.sub.P.sub.1.sub.+Q-1={tilde over (B)}.sub.Q-1, for the useful symbols (data, RS, control symbols) of the first part,

(29) $Y_{P_1+Q}={\tilde{B}}_0,\mathrm{.Math.},Y_{\frac{M}{2}-1}={\tilde{B}}_{P_2-1},$
for the cyclic postfix of the first part,
Y.sub.M/2=−Ã.sub.Q-P.sub.1, . . . , Y.sub.M/2+P.sub.1.sub.−1=−Ã.sub.Q-1, for the cyclic prefix of the second part,
Y.sub.P.sub.1.sub.+M/2−Ã.sub.0, Y.sub.P.sub.1.sub.+M/2+1=−Ã.sub.2, . . . , Y.sub.M-P.sub.2.sub.−1=−Ã.sub.Q-1, for the useful symbols (data, RS, control symbols) of the second part,
Y.sub.M-P.sub.2=−Ã.sub.0, . . . , Y.sub.M-1=−Ã.sub.P.sub.2.sub.−1, for the cyclic postfix of the second part.

(30) With Ã.sub.n=A*.sub.mod(−n+p−1,Q) and {tilde over (B)}.sub.n=B*.sub.mod(−n+p−1,Q) and X* is the complex conjugate of X.

(31) In a variant, zero padding can be used instead of cyclic prefix/postfix. In yet another variant, cyclic prefix and/or postfix can be inserted with respect to groups of symbols within the Q contiguous useful symbols, instead of being inserted with respect to the Q contiguous useful symbols.

(32) Therefore, Y can be defined, regarding the data, control and Reference signal symbols based on X by:

(33) $Y_k=\{\begin{array}{c}\mathrm{.Math.}{X}_{\frac{M}{2}+P_1+\mathrm{mod}\left(-k+P_1+p-1,Q\right)}^{*},\mathrm{for}k\in 〚P_1;\frac{M}{2}-P_2〛\\ -\mathrm{.Math.}{X}_{P_1+\mathrm{mod}\left(-k+P_1+\frac{M}{2} p-1,Q\right)}^{*},\mathrm{for}k\in 〚\frac{M}{2}+P_1;M-P_2〛\end{array}$

(34) With ε the value 1 or −1. When not stated otherwise, in the following we consider ε=1. Indeed, changing the sign (+/−) of the signal related to the second antenna does not change the method.

(35) Referring to FIG. 4 there is shown in detail the logical functioning of the specific SS-STBC like pre-coder module 2.2 and the specific Alamouti pairing structure induced by the specific SS-STBC like pre-coder module 2.2. That is, the FIG. 4 details the paring of symbols in the first block of M symbols according to the invention.

(36) When p is different from 0, the 0-th symbol A.sub.0 of the Q useful symbols of the first part of the first block of M symbols is paired with the p−1-th symbol B.sub.p−1 of the Q useful symbols of the second part of the first block of M symbols. Then the symbol A.sub.i is paired with the symbol B.sub.p−i for each i strictly smaller than p.

(37) Then the remaining symbols A.sub.p to A.sub.Q-1 of the Q useful symbols of the first part of the first block of M symbols are paired with the remaining symbols B.sub.Q-1 to B.sub.p of the Q useful symbols of the second part of the first block of M symbols, with: the first symbol A.sub.p of the first group (symbols Ap to A.sub.Q-1) being paired with the last symbol B.sub.Q-1 of the second group symbols (B.sub.p to B.sub.Q-1), the second symbol A.sub.p+1 of the first group (symbols A.sub.p to A.sub.Q-1) being paired with the before last symbol B.sub.Q-2 of the second group symbols (B.sub.p to B.sub.Q-1), and so on.

(38) When p is equal to zero, the first symbol A.sub.0 is paired with the last symbol B.sub.Q-1, the second symbol A.sub.1 is paired with the before last symbol B.sub.Q-2, and so on.

(39) Two symbols X.sub.a and X.sub.b of the first block of symbols are considered as paired when the position of the symbol issued from the symbol X.sub.a, that is the position a′ of the symbol Y.sub.a′ such as Y.sub.a′=±X*.sub.a is the position b. Therefore, the symbol X.sub.a and the symbol issued from X.sub.a, Y.sub.a′, are respectively in positions in the first and second block of symbols which are a and b, whereas the symbol X.sub.b and the symbol issued from X.sub.b are respectively in positions in the first and second block of symbol which are b and a.

(40) Referring to FIG. 5, it gives the details of the specific SS-STBC like pre-coder logical functioning with the p value set to ┌Q/2┐ according to an embodiment. In the example of FIG. 5 the sizes of P1, P2 and Q are set to simplify the presentation of this embodiment. Thus (P.sub.1, P.sub.2, Q)=(3,1,8). Of course, the present invention is not limited to such sizes of P1, P2 and Q.

(41) The maximal precoding distance between two symbols of an Alamouti pair is 15 symbols, that is between two symbols of an Alamouti pair there are only 14 symbols.

(42) Several configurations of the subcarrier mapping modules 2.5 and 2.6, are possible, for example the subcarrier mapping can be localized that is the M elements of each vector S.sup.Tx1,2 are mapped to M consecutive subcarriers among the N existing.

(43) Thus, when N is a multiple of M, the signal in the time domain at the output of the IDFT module 2.7, {tilde over (x)}.sup.Tx1=({tilde over (x)}.sup.Tx1.sub.0, . . . , {tilde over (x)}.sup.Tx1.sub.N-1), and at the output of the IDFT module 2.8, {tilde over (x)}.sup.Tx2=({tilde over (x)}.sup.Tx2.sub.0, . . . , {tilde over (x)}.sup.Tx2.sub.N-1), have respectively exact copies of the input time symbols X.sub.n and Y.sub.n (with a scaling factor) in the position M.n, that is {tilde over (x)}.sup.Tx1=({tilde over (x)}.sup.Tx1.sub.0=αX.sub.0, . . . , {tilde over (x)}.sup.Tx1.sub.M=αX.sub.1, . . . , {tilde over (x)}.sup.Tx1.sub.2M=αX.sub.2, . . . , {tilde over (x)}.sup.Tx1.sub.N-m=αX.sub.M-1) and {tilde over (x)}.sup.Tx2=({tilde over (x)}.sup.Tx2.sub.0=αY.sub.0, . . . , {tilde over (x)}.sup.Tx2.sub.M=αY.sub.1, . . . , {tilde over (x)}.sup.Tx2.sub.2M=αY.sub.2, . . . , {tilde over (x)}.sup.Tx2.sub.N-M=αY.sub.M-1).

(44) In the other positions the values of the samples in the first and second SC-FDMA symbols are respectively sums of all the X.sub.n and Y.sub.n with different complex-weighting. Therefore, {tilde over (x)}.sup.Tx1 and {tilde over (x)}.sup.Tx2 are respectively oversampled version of the first and second block of symbols. More explanations can be found in “Single carrier FDMA: a new air interface for long term evolution”, H G Myung, D J Goodman—John Wiley & Sons, 2008.

(45) Thus, the distance between two samples in the first SC-FDMA symbols {tilde over (x)}.sup.Tx1.sub.aM=αX.sub.a and {tilde over (x)}.sup.Tx1.sub.bM=αX.sub.b corresponding respectively to the two symbols of the Alamouti pair, that is M(b−a) samples, depends on the distance between the two Alamouti symbols in the first block of symbols which is of (b−a) symbols.

(46) The subcarrier mapping can also be distributed, that is the M elements of each vector S.sup.Tx1,2 are mapped equally distanced over the entire bandwidth with zero occupying the unused subcarriers.

(47) Thus, when N is a multiple of M, the signal in the time domain at the output of the IDFT module 2.7, {tilde over (x)}.sup.Tx1=({tilde over (x)}.sup.Tx1.sub.0, . . . , {tilde over (x)}.sup.Tx1.sub.N-1), and at the output of the IDFT module 2.8, {tilde over (x)}.sup.Tx2=({tilde over (x)}.sup.Tx2.sub.0, . . . , {tilde over (x)}.sup.Tx2.sub.N-1), have respectively N/M times repetition of the block of symbols X and Y, that is {tilde over (x)}.sup.Tx1=(αX.sub.0, αX.sub.1, . . . , αX.sub.M-1, . . . , αX.sub.0, αX.sub.1, . . . , αX.sub.M-1, αX.sub.0, αX.sub.1, . . . , αX.sub.M-1) and {tilde over (x)}.sup.Tx2=(αY.sub.0, αY.sub.1, . . . , αY.sub.M-1, . . . , αY.sub.0, αY.sub.1, . . . , αY.sub.M-1, αY.sub.0, αY.sub.1, . . . , αY.sub.M-1).

(48) Thus, the distance between two samples in the first SC-FDMA symbols {tilde over (x)}.sup.Tx1.sub.a+M.l=αX.sub.a and {tilde over (x)}.sup.Tx1.sub.b+M.l=αX.sub.b corresponding respectively to the two symbols of the Alamouti pair, that is (b−a) samples depends on the distance between the two Alamouti symbols in the first block of symbols which is of (b−a) symbols.

(49) By distance between two samples it is understood the time difference (or time duration) between the emission in the radio signal of these two samples.

(50) Therefore, the distance between two samples corresponding respectively to symbols of an Alamouti pair is proportional or at least dependent on the distance of these symbols in the first block of symbols.

(51) This is the case for all the other subcarrier mapping types and/or non-integer N/M ratios similar relationships between the symbols and their corresponding samples in the radio signal.

(52) Therefore, by minimizing the maximal precoding distance in the first block of symbols between two symbols of the same pair it minimizes the maximum time duration between samples in the radio signal corresponding to two symbols of the same pair. This enables to minimize the channel changes between the emission of samples in the first and second SC-FDMA symbol corresponding to the symbol X.sub.a. By minimizing the channel changes between these emissions of samples it reduces orthogonality loss between symbols of the same Alamouti pair which leads to interferences and performance loss.

(53) The minimizing of the maximum precoding distance between two symbols of the same pair is obtained when the p value is set to a value around Q/2, and specifically when p is equal to ┌Q/2┐ and/or └Q/2┘.

(54) Referring to FIG. 6, details of the specific SS-STBC like pre-coder logical functioning with the p value set to K according to an embodiment. In this example the sizes of P1, P2 and Q are set to simplify the presentation of this embodiment. Thus (P.sub.1, P.sub.2, Q)=(3,1,8). Of course, the present invention is not limited to such sizes of P1, P2 and Q.

(55) The K first symbols of the useful part of the first part of the first block of symbols are paired with the K first symbols of the useful part of the second part of the first block of symbols. Thus, the K symbols issued from the pre-coder from the K first symbols of the useful part of the first part of the first block of symbols are the K first symbols of the useful part of the second part of the second block of symbols.

(56) Thus, the K first symbols of the useful part of the first part of the first block of symbols and their issued (from the pre-coder) symbols are both positioned behind P1 prefix symbols, which enables to protect these 2K symbols from interferences, especially multipath interferences. Note that, in a variant, the prefix can be inserted with respect to the K first symbols of each useful part and not to the Q symbols. That is, the prefix inserted within the first block of symbols contains symbols A.sub.K-P1 . . . A.sub.K-1 and B.sub.K-P1 . . . B.sub.K-1 respectively.

(57) Since the K issued symbols enable to ease the retriever of the K first symbols of the useful part of the first part of the first block of symbols, the K first symbols of the first part forming a group G are more robust to interference. It is therefore, relevant to insert in the group G symbols which specifically need to be protected from interference as reference signal symbols and/or control symbols since they are particularly important for decoding properly the other symbols.

(58) Referring to FIG. 7, it gives the details of the specific SS-STBC like pre-coder logical functioning with the p value set to 0 according to an embodiment. In this example the sizes of P1, P2 and Q are set to simplify the presentation of this embodiment. Thus (P.sub.1, P.sub.2, Q)=(3,1,8). Of course, the present invention is not limited to such sizes of P1, P2 and Q.

(59) In this embodiment, the first symbol of the useful part of the first part of the first block of symbols is paired with the last symbol of the useful part of the second part of the first block of symbols. The second symbol of the useful part of the first part of the first block of symbols is paired with the before last symbol of the useful part of the second part of the first block of symbols, and so on. This Alamouti pairing structure is of low complexity for the pre-coder.

(60) Based on such a structure it is possible to define several groups having K.sub.i symbols each, these several groups being symmetrically arranged. That is, by defining the i-th first group G.sub.i of K.sub.i symbols as the group composed of the symbols from the (P.sub.1+Σ.sub.j=1.sup.i-1K.sub.j)-th symbol

(61) $X_{P_1+\underset{j=1}{\overset{i-1}{.Math.}}{K}_j}$
to the (P.sub.1+Σ.sub.j=1.sup.iK.sub.j−1)-th symbol

(62) $X_{P_1+\underset{j=1}{\overset{i}{.Math.}}{K}_j-1}$
of the first block of M symbols; and

(63) by defining the i-th first group G′.sub.i of K.sub.i symbols as the group composed of the symbols from the (M−P.sub.2−Σ.sub.j=1.sup.iK.sub.j)-th symbol

(64) $X_{M-P_2-\underset{j=1}{\overset{i}{.Math.}}{K}_j}$
to the (M−P.sub.2−Σ.sub.j=1.sup.i-1K.sub.j−1)-th symbol

(65) 0$X_{M-P_2-\underset{j=1}{\overset{i-1}{.Math.}}{K}_j-1}$
of the first block of M symbols.

(66) Therefore, the symbols of the i-th group G.sub.i are paired with the symbols of the group G′.sub.i. The group G.sub.i and the group G′.sub.i are called paired groups. The samples in the first and second SC-FDMA symbols corresponding to symbols of the i-th group are emitted at the same time than the samples in the first and second SC-FDMA symbols corresponding to symbols of the paired group G′.sub.i. Therefore, it is possible to separate at the receiver side the processing of samples corresponding to the symbols of a group and its paired group from the processing of other samples corresponding to symbols of other groups.

(67) If the symbols of paired groups are of the same type, for example data symbol, reference signal symbol or control symbol, then at the receiver side it is possible to separate the processing of for example the reference signal part of the radio signal.

(68) In addition, setting the p value, P.sub.1 and P.sub.2 to zero and having such specific group structure is convenient to insert reference signals according to the PTRS insertion patterns for DFTsOFDM PUSCH described in the 3GPP TS 38.211 Table 6.4.1.2.2.2-1 clause 6.4.1.2.2. Indeed, these insertion patterns are symmetric, that is for example the N.sub.group.sup.PTRS first symbols and the N.sub.group.sup.PTRS last symbols of the first block of symbols are set as reference signals. Thus, by setting K.sub.1 to N.sub.group.sup.PTRS the group structure is made compatible with such insertion pattern.

(69) In another example the RSs are inserted in the middle of each half of the first block of symbols, that is in the position (M/4−1; M/4) and (3M/4−1, 3M/4) when inserting two groups of two RS samples each. Thus for example by setting K.sub.2 to 2 and K.sub.1 to M/4−1 the group structure is made compatible with such insertion pattern. Thus, more generally, setting K.sub.i=2 such as

(70) $\underset{j=1}{\overset{i-1}{.Math.}}{K}_j=\frac{M}{4}-1\mathrm{and}{G}_i=\left\{\frac{M}{4}-1,\frac{M}{4}\right\},G_i^{\prime }=\left\{\frac{3M}{4}-1,\frac{3M}{4}\right\}$
the group structure is made compatible with such insertion pattern.

(71) In another example the symbols of the paired groups in which should be inserted the RSs are set to zero in the first block of symbols before applying the pre-coder. The RS are then inserted after applying the pre-coder in replacement to the zeros. For example this insertion can be made before applying the DFT modules 2.3 and 2.4 that is by setting the symbols set to zero in the first and second block of symbols to the desired values. In the case of reference signals, since their values are known by the receiver, there is no need to have the values of the reference signals inserted in the second block of symbols equal to the values of these symbols that would have been obtained if the reference signals inserted in the first block of symbols would have been pre-coded. As an equivalent implementation option, reference signals can be inserted after DFT (that is in the frequency domain) or after IDFT by adding a corresponding signal to obtain the same or equivalent signal as if the reference signal where inserted before applying the DFT.

(72) Referring to FIG. 8, illustrates a flowchart representing the steps for transmitting symbols in the radio signal according to the invention.

(73) At step S1 the parameters used to configure the pre-coder module 2.2 are determined. That is, the p value, the size of P.sub.1, P.sub.2 and M are determined. These parameters are called the pre-coder's parameters.

(74) This determination of the parameters is done according to the scheme of the communication and/or the configuration of the cell determined by the base station 1.2.

(75) In the case where the transmitter is a mobile terminal, the base station 1.2 can previously determine the parameters of the communication and set the pre-coder's parameters of the transmitter 1.1.

(76) Information representative of the pre-coder's parameters can be sent to the transmitter 1.1. Therefore, the transmitter 1.1 receives information representing or allowing to compute the p value and the size of P.sub.1, P.sub.2 and M based on which the transmitter 1.1 can determine effectively the p value and the size of P.sub.1, P.sub.2 and M.

(77) For example, the base station 1.2 can transmit to the transmitter 1.1: a cell specific p value information; and/or a transmitter specific p value information; and/or the size of P.sub.1, P.sub.2 and M.

(78) These parameters and especially the p value can be determined for example by the base station 1.2 based on: a cell-specific configuration and/or dynamic control indication for example a DCI indicator/format and/or; a reference signal, RS, configuration/insertion pattern and/or; user-specific parameters such as (but not limited to) modulation and coding scheme, resource allocation size and/or; a p′ value used by another transmitter in the same cell and/or; sets of predetermined values (p.sub.i, P.sub.1i, P.sub.2i, M.sub.i).

(79) The p value may also be determined randomly by the base station 1.2 among a set of predetermined values.

(80) In an alternative the base station 1.2 does not send to the mobile terminal 1.1 the information representing the p value and the size of P.sub.1, P.sub.2 and M, but sends one of the above mention information based on which the terminal 1.1 can deduce the pre-coder parameters set by the base station 1.2. For example, the use of a specific reference signal configuration can be related to specific pre-coder's parameters.

(81) In an alternative embodiment the base station 1.2 can determine the scheme of the communication (for examples the RS insertion pattern, the Modulation and Coding Scheme, MCS, . . . ) and/or the configuration of the cell but not the pre-coder's parameters, leaving the transmitter 1.1 determine and/or compute the parameters according to the communication scheme. In this case, the transmitter 1.1 may once the pre-coder's parameters determined send to the base station 1.2 information enabling the base station 1.2 to retrieve the pre-coder's parameters.

(82) In the case where the transmitter 1.1 is the base station and the receiver 1.2 is the mobile terminal, the base station 1.1 determines the parameters used to configure the pre-coder module 2.2 of the base station 1.1. That is, the p value, the size of P.sub.1, P.sub.2 and M are set. These parameters are called the pre-coder's parameters.

(83) These parameters and especially the p value to be used when communicating with the receiver 1.2 can be determined by the base station 1.1 base on: a cell-specific configuration; a reference signal, RS, configuration/insertion pattern; user-specific parameters determined for the receiver 1.2; a p′ value used by an adjacent base station; sets of predetermined values (p.sub.i, P.sub.1i, P.sub.2i, M.sub.i).

(84) Additionally, like in the previous embodiments the base station 1.1 provides the mobile terminal 1.2 information allowing the mobile terminal 1.2 to deduce the parameters used by the pre-coder, thus enabling the mobile terminal 1.2 to decode the received communication.

(85) Additionally, in both cases, the mobile terminal being either the receiver 1.2 or the transmitter 1.1, the mobile terminal can deduce these parameters based on a rule commonly known by both the base station and the mobile terminal.

(86) In yet another example, both the transmitter and the receiver are mobile terminals. The p value can be determined based on predetermined rules or by cooperation.

(87) (e.g. each mobile terminal determines the p value to be used for its own communication and transfers it to the other;

(88) e.g. each mobile terminal determines the p value to be used for its own communication and the other terminal can implicitly determine the used value from other information;

(89) e.g. one terminal decides the p value to be used during communication in both directions and transfers it to the other;

(90) e.g. one terminal decides the p value to be used during communication in both directions and the other terminal can implicitly determine the used value from other information;

(91) e.g. terminals exchange information allowing to determine a common p value;

(92) e.g. both terminals apply a set of known rules, allowing them to unambiguously determine the p value based on other known parameters/configurations; e.g. the p value is fixed for all sidelink communication, etc)

(93) At step S3 the pre-coder module 2.2 is configured according to the pre-coder's parameters determined by the terminal 1.1.

(94) At step S5 the signal is processed, that is on the first block of symbols X(X.sub.0, . . . X.sub.M-1) is applied the specific SS-STBC like pre-coder module 2.2 previously configured to obtain the second block of symbols Y=(Y.sub.0, . . . Y.sub.M-1). Then on each of the first and second blocks of symbols is applied an SC-FDMA scheme (DFT modules 2.3 and 2.4, subcarrier mapping modules 2.5 and 2.6, IDFT modules 2.7 and 2.8).

(95) At step S7 the signal is emitted by Tx1 2.0 and Tx2 2.1.