Patent ID: 12218785

MODE FOR INVENTION

The present disclosure may have various changes thereto and various embodiments, and thus particular embodiments will be illustrated in the drawings and described in detail.

It should be understood, however, that this is not intended to limit the present disclosure to a particular embodiment of the present disclosure, and should be understood to include all changes, equivalents, and alternatives falling within the spirit and scope of the present disclosure.

The terms, first, second, etc., may be used to describe various components, but the components are not limited by these terms. These terms are used to distinguish one component from another component. For example, a first component may be referred to as a second component without departing from the scope of the disclosure, and similarly, the second component may be referred to as the first component.

When an element is referred to as being “connected” or “accessed” to or by any other element, it should be understood that the element may be directly connected or accessed by the other element, but another new element may also be interposed therebetween. Contrarily, when an element is referred to as being “directly connected” or “directly accessed” to or by any other element, it should be understood that there is no new another element therebetween.

The term used herein is used to describe particular embodiments, and is not intended to limit the present disclosure. Singular forms include plural forms unless apparently indicated otherwise contextually. Moreover, it should be understood that the term “include”, “have”, or the like used herein is to indicate the presence of features, numbers, steps, operations, elements, parts, or a combination thereof described in the specifications, and does not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, parts, or a combination thereof.

All of the terms used herein including technical or scientific terms have the same meanings as those generally understood by those of ordinary skill in the art of the disclosure, unless they are defined other. The terms defined in a generally used dictionary should be interpreted as having the same meanings as the contextual meanings of the relevant technology and should not be interpreted as having ideal or exaggerated meanings unless they are clearly defined in the present application.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present disclosure will be described clearly and in detail such that those of ordinary skill in the art may easily carry out the present disclosure.

FIG.1is a block diagram showing a structure of a discrete Fourier transform (DFT)-spread orthogonal frequency division multiplexing (OFDM) transmitter according to an embodiment of the present disclosure,FIG.2is a block diagram showing in detail a constellation rotation unit ofFIG.1,FIG.3is a block diagram showing in detail a pruned DFT-spread unit ofFIG.1, andFIG.4is a block diagram showing in detail a frequency domain spectrum shaping unit ofFIG.1.

Referring toFIG.1, a DFT-spread OFDM transmitter100according to an embodiment of the present disclosure may include a constellation rotation unit110, a pruned DFT-spread unit120, a frequency domain spectrum shaping unit130, a subcarrier allocation unit140, and a signal generation unit150. The signal generation unit150may include an N-point inverse DFT (IDFT) unit151and a cyclic prefix (CP) insertion unit153.

The constellation rotation unit110may constellation-rotate a symbol vector b including M pulse amplitude modulation (PAM) symbols by a constellation rotation angle ϕ to generate a constellation-rotated symbol vector d. As shown inFIG.2, the constellation-rotated symbol vector d may be generated by d=R(ϕ)b, and a diagonal matrix R(ϕ) may be defined by Equation 1.
R(ϕ)≙diag{ejϕ·0,ejϕ·1, . . . ,ejϕ·(M−1)}  Equation (1)

The constellation rotation angle ϕ may be determined based on a length M of the symbol vector b and the number L of allocated subcarriers. More specifically, the constellation rotation angle ϕ may be determined by Equation 2 for M being an even number, and by Equation 3 for M being an odd number.

ϕproposed=mod⁢{(L-1)⁢πM+π2,π}Equation⁢(2)ϕproposed=mod⁢{(L-1/2)⁢πM+π2,π}Equation⁢(3)

In Equation 2 and Equation 3, mod{⋅} may be a modulo operation.

The pruned DFT-spread unit120may spread the constellation-rotated symbol vector d by using a pruned DFT matrix WL,Mto generate a pruned DFT-spread vector c. As shown inFIG.3, the pruned DFT-spread vector c may be generated by c=WL,MR(ϕ)b, and the pruned DFT matrix WL,Mmay be a matrix with an L×M size in which the last (M−L) rows are removed from an M-point DFT matrix WM. An element (i, j) of the pruned DFT matrix WL,Mmay be determined by Equation 4.

[WL,M](i,j)=1M⁢e-j⁢2⁢πM⁢(i-1)⁢(j-1)Equation⁢(4)

In Equation 4, indices i and j respectively satisfy 1≤i≤L, and 1≤j≤M.

The frequency domain spectrum shaping unit130may Hadamard-multiply (perform a Hadamard product) the pruned DFT-spread vector c with the shaping vector s to generate a frequency domain spectrum shaped vector a. Alternatively, as shown inFIG.4, the frequency domain spectrum shaped vector a may be generated by multiplying a matrix diag{s} having the shaping vector s as a diagonal element to the pruned DFT-spread vector c. A shaping vector s with an L×1 size may be defined by Equation 5.
s=[s0,s1, . . . ,sL−1]  Equation (5)

Each element of the shaping vector s may be determined based on the length M of the symbol vector b and the number L of allocated subcarriers. More specifically, an Ith element of the shaping vector s may be determined by Equation 6 for M being an even number, and by Equation 7 for M being an odd number.

sproposed,l=Δ{2⁢sin⁢(π⁡(l+12)2⁢L-M),for⁢0≤l≤L-M2-1,2⁢cos⁢(π⁡(l-M2+12)2⁢L-M),for⁢M2≤l≤L-1,2,elsewhere,Equation⁢(6)sproposed,l=Δ{2⁢sin⁢(π⁡(l+14)2⁢L-M),for⁢0≤l≤L-M+12,2⁢cos⁢(π⁡(l-M2+14)2⁢L-M),for⁢M+12≤l≤L-1,2,elsewhere,Equation⁢(7)

In Equation 6 and Equation 7, l=0, 1, 2, . . . , L−1 and M/2≤L≤M may be satisfied.

The subcarrier allocation unit140may allocate the frequency domain spectrum shaped vector a to a subcarrier in an allocated frequency range. When the frequency domain spectrum shaped vector a is allocated to the subcarrier, it passes through the N-point IDFT unit151and the CP insertion unit153to generate a DFT-spread OFDM signal x. Operations of the N-point IDFT unit151and the CP insertion unit153are widely known to the technical field to which the present disclosure belongs, and thus will not be described herein.

FIG.5is a flowchart of a DFT-spread OFDM transmission method, according to an embodiment of the present disclosure.

The DFT-spread OFDM transmission method according to an embodiment of the present disclosure may be performed by the DFT-spread OFDM transmitter100ofFIG.1.

Referring toFIG.5, in operation S510, a symbol vector b including M PAM symbols may be constellation-rotated by a constellation rotation angle ϕ to generate a constellation-rotated symbol vector d. The constellation rotation angle ϕ may be determined by Equation 2 for M being an even number, and by Equation 3 for M being an odd number.

In operation S520, the constellation-rotated symbol vector d may be spread by using a pruned DFT matrix WL,Mto generate a pruned DFT-spread vector c. An element (i, j) of the pruned DFT matrix WL,Mmay be determined by Equation 4.

In operation S530, the pruned DFT-spread vector c may be Hadamard-multiplied with the shaping vector s to generate a frequency domain spectrum shaped vector a. An Ith element of the shaping vector s may be determined by Equation 6 for M being an even number, and by Equation 7 for M being an odd number.

In operation S540, the frequency domain spectrum shaped vector a may be allocated to a subcarrier in an allocated frequency range.

In operation S550, when the frequency domain spectrum shaped vector a is allocated to the subcarrier, N-point IDFT may be performed and a CP may be inserted to generate a signal.

FIG.6is a block diagram showing a structure of a DFT-spread OFDM receiver, according to an embodiment of the present disclosure.

Referring toFIG.6, a DFT-spread OFDM receiver600according to an embodiment of the present disclosure may include a CP removal unit610, an N-point DFT unit620, a frequency domain reception spectrum shaping unit630, a pruned IDFT unit640, an inverse constellation rotation unit650, and an estimation unit660.

The CP removal unit610may receive a signal passing through a channel and remove a CP from the signal y to generate a CP-removed vector {tilde over (y)}.

The N-point DFT unit620may perform N-point DFT on the CP-removed vector {tilde over (y)} and cut out a part corresponding to the subcarrier in the allocated frequency range from a result to generate a vector ã. Although it is shown inFIG.6that the vector ã resulting from cutout of the part corresponding to the subcarrier in the allocated frequency range corresponds to first L subcarriers, the present disclosure is not limited thereto. Hereinbelow, assuming allocation to the first L subcarriers, the vector ã may be defined by Equation 8.
ã≙[ILOL×(N−L)]WN{tilde over (y)}Equation (8)

Herein, ILmay be an L×L unit matrix and OL×(N−L)may be an L×(N −L) zero matrix.

The frequency domain reception spectrum shaping unit630may the vector ã resulting from cutout of the part corresponding to the subcarrier in the allocated frequency range by a conjugate complex vector of the reception shaping vector sRto generate a frequency domain reception spectrum shaped vector.

The pruned IDFT unit640may multiply a prefixed pruned DFT matrix WL,MHto the frequency domain reception spectrum shaped vector to generate a despread vector.

The inverse constellation rotation unit650may inversely constellation-rotate the despread vector by an inverse constellation rotation angle −ϕ to generate the inversely constellation-rotated vector.

The estimation unit660may take a real number part of the inversely constellation-rotated vector to generate an estimated valueof a transmitted PAM symbol vector. Thus, the estimated valueof the PAM symbol vector may be expressed as Equation 9.
{circumflex over (b)}=Re[R(−ϕ)WL,MHdiag{sR*}ã]Equation (9)

Herein, sRmay be an L x 1 reception shaping vector, an upper subscript * may mean conversion to a conjugate complex vector, and the inverse constellation rotation angle −ϕ may be a negative number of a transmission rotation angle.

The estimated valueof the PAM symbol vector may be expressed as Equation 10 by using an L x 1 frequency domain channel diagonal matrix.
{circumflex over (b)}=Re{R(−ϕ)WL,MHdiag{sR*}{tilde over (H)}diag{s}WL,MR(ϕ)}b+noise  Equation (10)

Herein, the frequency domain channel diagonal matrix {tilde over (H)} may be expressed as Equation 11 by using an N×N channel diagonal matrix H.
{tilde over (H)}=[ILOL×(N−L)]WNHWNH[ILOL×N−L)]HEquation (11)

Meanwhile, when a channel is a frequency-flat, the reception shaping vector sRmay be selected identically to a transmission shaping vector.

FIG.7is a flowchart of a DFT-spread OFDM reception method, according to an embodiment of the present disclosure.

The DFT-spread OFDM reception method according to an embodiment of the present disclosure may be performed by the DFT-spread OFDM receiver600ofFIG.6.

Referring toFIG.7, in operation S710, a signal y passing through a channel may be received and a CP may be removed from the signal y to generate a CP-removed vector {tilde over (y)}.

In operation S720, N-point DFT may be performed on the CP-removed vector {tilde over (y)} and a part corresponding to the subcarrier in the allocated frequency range may be pruned from a result to generate a vector ã. Assuming allocation to the first L subcarriers, the vector ã may be defined by Equation 8.

In operation S730, the vector ã resulting from cutout of the part corresponding to the subcarrier in the allocated frequency range may be Hadamard-multiplied by a conjugate complex vector of the reception shaping vector sRto generate a frequency domain reception spectrum shaped vector.

When the channel is frequency-flat, the reception shaping vector sRmay be selected identically to the transmission shaping vector.

In operation S740, a prefixed pruned DFT matrix WL,MHmay be multiplied to the frequency domain reception spectrum shaped vector to generate a despread vector.

In operation S750, the despread vector may be inversely constellation-rotated by an inverse constellation rotation angle −ϕ to generate the inversely constellation-rotated vector.

In operation S760, a real number part of the inversely constellation-rotated vector may be taken to generate an estimated valueof a transmitted PAM symbol vector. The estimated valueof the PAM symbol vector may be expressed as Equation 9.

FIG.8is a graph showing frequency efficiency with respect to the number of BPSK symbols transmitted in fixed subcarriers.

FIG.8shows frequency efficiency when a length of a constellation-rotated BPSK symbol vector, M, changes from 24 to 28 in case of allocation of L=24 subcarriers. Referring toFIG.8, for M=24, a constellation rotation angle and a shaping vector according to embodiments of the present disclosure may have the same frequency efficiency as when spectrum shaping is not performed, and may improve the frequency efficiency up to twice when spectrum shaping is not performed, for M being increased to 48.

FIG.9is a graph showing PAPR performance with respect to the number of BPSK symbols transmitted in fixed subcarriers.

FIG.9shows a PAPR value when a length of a constellation-rotated BPSK symbol vector, M, changes from 24 to 28 in case of allocation of L=24 subcarriers. Referring toFIG.9, for M=24, a constellation rotation angle and a shaping vector according to embodiments of the present disclosure may have a much lower PAPR performance than when spectrum shaping is not performed, and in particular, for 24<M≤44, the constellation rotation angle and the shaping vector according to embodiments of the present disclosure may have a better frequency efficiency while having a low PAPR performance than when spectrum shaping is not performed. A case with 44<M≤48 may have a PAPR performance that is similar to or higher than that of a conventional pi/2-BPSK symbol, but may have a higher frequency efficiency. Thus, by using the constellation rotation angle and the shaping vector according to embodiments of the present disclosure, the PAPR performance and the frequency efficiency may be easily traded off with each other.

Although it has been described with reference to the drawings and embodiments above, it does not mean that the scope of protection of the present disclosure is limited by the drawings or the embodiments, and those of ordinary skill in the art may understand that various modifications and changes may be made to the present disclosure without departing from the spirit and the scope of the present disclosure described in the claims.

DESCRIPTION OF REFERENCE NUMERALS

100: DFT-SPREAD OFDM TRANSMITTER110: CONSTELLATION ROTATION UNIT120: PRUNED DFT-SPREAD UNIT130: FREQUENCY DOMAIN SPECTRUM SHAPING UNIT140: SUBCARRIER ALLOCATION UNIT150: SIGNAL GENERATION UNIT151: N-POINT IDFT UNIT153: CYCLIC PREFIX INSERTION UNIT600: DFT-SPREAD OFDM RECEIVER610: CYCLIC PREFIX REMOVAL UNIT620: N-POINT DFT UNIT630: FREQUENCY DOMAIN RECEPTION SPECTRUM SHAPING UNIT640: PRUNED IDFT UNIT650: INVERSE CONSTELLATION ROTATION UNIT660: ESTIMATION UNIT