Apparatus and method for generating symbol for multiple antennas
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 WO2008056856A1 WO2008056856A1 PCT/KR2007/001229 KR2007001229W WO2008056856A1 WO 2008056856 A1 WO2008056856 A1 WO 2008056856A1 KR 2007001229 W KR2007001229 W KR 2007001229W WO 2008056856 A1 WO2008056856 A1 WO 2008056856A1
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 H—ELECTRICITY
 H04—ELECTRIC COMMUNICATION TECHNIQUE
 H04B—TRANSMISSION
 H04B7/00—Radio transmission systems, i.e. using radiation field
 H04B7/02—Diversity systems; Multiantenna systems, i.e. transmission or reception using multiple antennas
 H04B7/04—Diversity systems; Multiantenna systems, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
 H04B7/06—Diversity systems; Multiantenna systems, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
 H04B7/0613—Diversity systems; Multiantenna systems, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
 H04B7/0667—Diversity systems; Multiantenna systems, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal
 H04B7/0669—Diversity systems; Multiantenna systems, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal using different channel coding between antennas

 H—ELECTRICITY
 H04—ELECTRIC COMMUNICATION TECHNIQUE
 H04B—TRANSMISSION
 H04B7/00—Radio transmission systems, i.e. using radiation field
 H04B7/02—Diversity systems; Multiantenna systems, i.e. transmission or reception using multiple antennas
 H04B7/04—Diversity systems; Multiantenna systems, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
 H04B7/06—Diversity systems; Multiantenna systems, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
 H04B7/0613—Diversity systems; Multiantenna systems, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
 H04B7/0667—Diversity systems; Multiantenna systems, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal
 H04B7/0671—Diversity systems; Multiantenna systems, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal using different delays between antennas

 H—ELECTRICITY
 H04—ELECTRIC COMMUNICATION TECHNIQUE
 H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
 H04L1/00—Arrangements for detecting or preventing errors in the information received
 H04L1/02—Arrangements for detecting or preventing errors in the information received by diversity reception
 H04L1/06—Arrangements for detecting or preventing errors in the information received by diversity reception using space diversity
 H04L1/0606—Spacefrequency coding

 H—ELECTRICITY
 H04—ELECTRIC COMMUNICATION TECHNIQUE
 H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
 H04L1/00—Arrangements for detecting or preventing errors in the information received
 H04L1/02—Arrangements for detecting or preventing errors in the information received by diversity reception
 H04L1/06—Arrangements for detecting or preventing errors in the information received by diversity reception using space diversity
 H04L1/0618—Spacetime coding
 H04L1/0625—Transmitter arrangements

 H—ELECTRICITY
 H04—ELECTRIC COMMUNICATION TECHNIQUE
 H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
 H04L1/00—Arrangements for detecting or preventing errors in the information received
 H04L1/02—Arrangements for detecting or preventing errors in the information received by diversity reception
 H04L1/06—Arrangements for detecting or preventing errors in the information received by diversity reception using space diversity
 H04L1/0618—Spacetime coding
 H04L1/0637—Properties of the code
 H04L1/0668—Orthogonal systems, e.g. using Alamouti codes

 H—ELECTRICITY
 H04—ELECTRIC COMMUNICATION TECHNIQUE
 H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
 H04L27/00—Modulatedcarrier systems
 H04L27/26—Systems using multifrequency codes
 H04L27/2601—Multicarrier modulation systems
Abstract
Description
[DESCRIPTION]
[Invention Title]
APPARATUS AND METHOD FOR GENERATING SYMBOL FOR MULTIPLE ANTENNAS [Technical Field]
The present invention relates to a symbol generation method for multiple antennas, and an apparatus thereof. More particularly, the present invention relates to a symbol generation method for multiple antennas having low receiving complexity and having flexibility with respect to an increase of the number of antennas, and an apparatus thereof. [Background Art]
Diversity gains and receiving complexity are considered important performance measures when a multiple antenna communication system is designed. Various multiple antenna transmission methods for obtaining a maximum diversity gain have been suggested, and one of them is an Alamouti transmission method.
According to the Alamouti transmission method, a signal transmitting apparatus includes two transmitting antennas and a data rate is 1. Since the Alamouti transmission method has low complexity while having a maximum diversity gain, it is widely used. However, when the signal transmitting apparatus uses more than three transmitting antennas, the data rate may not be 1 to obtain the maximum diversity gain and the low receiving complexity. In addition, there is a problem in that the receiving complexity may be considerably increased in order to obtain the maximum diversity gain and the data rate of 1.
To solve the above problem, a method in which two respective Alamouti transmission blocks as given in Equation 1 are used when the number of transmitting antennas is 4 has been suggested ("IEEE802.16e/D12, Part 16: Air interface for fixed and mobile broadband wireless access systems", Oct. 2005, p.473474).
(Equation 1)
In Equation 1 , respective rows in a matrix are signals transmitted to respective transmitting antennas, first and third columns are signals transmitted at a time k, and second and fourth columns are signals transmitted at a time K+1. The Alamouti transmission block including the first and second columns and the Alamouti transmission block including the third and fourth columns are transmitted by using different orthogonal resources (different subcarriers in a case of orthogonal frequency division multiplexing).
However, the transmission method as in Equation 1 submits to loss of the diversity gain to achieve the low receiving complexity and the data rate of 1. In addition, it is not appropriately used for a transmitting apparatus having 3 or 5 transmitting antennas. [Disclosure]
[Technical Problem] The present invention has been made in an effort to provide a symbol generation method for multiple antennas having low receiving complexity and having flexibility with respect to an increase of the number of antennas, and an apparatus thereof.
[Technical Solution] An exemplary symbol generation apparatus according to an embodiment of the present invention includes a plurality of spacetime channel encoders, and an inverse fast Fourier transformer. The plurality of spacetime channel encoders respectively correspond to a plurality of channels, receive a digitalmodulated symbol group from the corresponding channel, perform spacetime encoding with respect to a plurality of space areas and at least one time area, shift phases by using a plurality of phases, and generate a plurality of phaseshifted spacetime codewords. The inverse fast Fourier transformer performs an inverse fast Fourier transform operation by using the plurality of phaseshifted spacetime codewords in a plurality of subcarriers respectively corresponding to the plurality of channels, and generates a plurality of inverse fast Fourier transformed signals
In this case, the plurality of phase values used by the respective space time channel encoders may respectively have different values, and may be proportional to the corresponding subcarrier.
An exemplary symbol generation apparatus according to another embodiment of the present invention includes a plurality of spacefrequency channel encoders, and an inverse fast Fourier transformer group. The plurality of spacefrequency channel encoders respectively correspond to a plurality of channels, receive a digitalmodulated symbol group from the corresponding channel, perform a spacefrequency encoding operation with respect to a plurality of space areas and at least one frequency area, shift phases by using a plurality of phase values, and generate a plurality of phaseshifted space frequency codewords. The inverse fast Fourier transformer group performs an inverse fast Fourier transform operation in a plurality of subcarrier groups respectively corresponding to the plurality of channels by using the phase shifted spacefrequency codewords, and generates a plurality of inverse fast Fourier transformed signals. The respective subcarrier groups include at least one subcarrier respectively corresponding to the at least one frequency area.
An exemplary symbol generation apparatus according to a further embodiment of the present invention includes a spacetime channel encoder, a spacefrequency channel encoder, and an inverse fast Fourier transformer group. The spacetime channel encoder receives a digitalmodulated symbol group, performs a spacetime encoding operation with respective to a plurality of space areas and at least one time area, shifts phases by using a plurality of phase values, and generates a phaseshifted spacetime codeword. The spacefrequency channel encoder receives the digitalmodulated symbol group, performs a spacefrequency encoding operation with respect to the plurality of space areas and at least one frequency area, shifts phases by using the plurality of phase values, and generates a phaseshifted spacefrequency codeword. The inverse fast Fourier transformer group inverse fast Fourier transforms the phaseshifted spacetime codeword in a subcarrier corresponding to the phaseshifted spacetime codeword, inverse fast Fourier transforms the phaseshifted spacefrequency codeword in a plurality of subcarriers respectively corresponding to the plurality of frequency areas, and generates a plurality of inverse fast Fourier transformed signals.
In an exemplary symbol generation method according to an embodiment of the present invention, a digitalmodulated symbol group is received, a space time encoding operation is performed with respect to a plurality of space areas and at least one time area, a spacetime codeword is generated, phases of a plurality of symbols in the spacetime codeword are respectively shifted by using phase values corresponding to a number according to the space area, a phaseshifted spacetime codeword is generated, an inverse fast Fourier transform operation is performed by using the phaseshifted spacetime codeword in a subcarrier corresponding to the phaseshifted spacetime codeword, and a plurality of inverse fast Fourier transformed signals are generated.
[Description of Drawings] FIG. 1 is a diagram of a signal transmitting apparatus according to a first exemplary embodiment of the present invention.
FIG. 2 is a diagram representing a notion of cyclic delay. FIG. 3 is a diagram of a signal transmitting apparatus according to a second exemplary embodiment of the present invention.
FIG. 4 is a flowchart representing an operation of the signal transmitting apparatus according to the second exemplary embodiment of the present invention.
FIG. 5 is a diagram representing a notion of a spacetime codeword. FIG. 6 is a diagram representing a phaseshifted spacetime codeword generated by a spacetime channel delay unit.
FIG. 7 is a diagram of a signal transmitting apparatus according to a third exemplary embodiment of the present invention.
FIG. 8 is a flowchart representing an operation of the signal transmitting apparatus according to the third exemplary embodiment of the present invention. FIG. 9 is a diagram representing a notion of a spacefrequency codeword.
FIG. 10 is a diagram representing a notion of a phaseshifted space frequency codeword generated by a spacefrequency channel delay unit. FIG. 11 is a diagram of a signal transmitting apparatus according to a fourth exemplary embodiment of the present invention. [Best Mode] In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.
In addition, unless explicitly described to the contrary, the word "comprise" and variations such as "comprises" or "comprising" will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.
A signal transmitting apparatus 100 according to a first exemplary embodiment of the present invention will be described with reference to FIG. 1 and FIG. 2. FIG. 1 is a diagram of the signal transmitting apparatus 100 according to the first exemplary embodiment of the present invention. The signal transmitting apparatus 100 as shown in FIG. 1 encodes and transmits a signal at a time area, and it includes a spacetime encoder 110, G delay unit groups 120, and G antenna groups 130. The spacetime encoder 110 spacetime encodes an input signal s(n) with respect to G space areas and at least one time area, and generates G encoding signals Xi(n) to XG(Π). The spacetime encoder 110 may be substituted by a frequencyspace encoder, which will be described later. The G delay unit groups 120 respectively correspond to the G space areas. The delay unit group 120 corresponding to a space area g cyclically delays encoding signals x_{g}(n) by N_{9} delay values and generates N_{9} delayed encoding signals. Cyclic delay will be described with reference to FIG. 2. FIG. 2 is a diagram representing the cyclic delay.
An encoding signal x_{g}(n) is a symbol of a symbol period T that is not delayed. When the delay unit group 120 corresponding to the space area g cyclically delays the encoding signal x_{g}(n) through three delay values 0, T/4, and T/2, the delay unit group 120 corresponding to the space area g generates three delay signals A_{g}(n), B_{g}(n), and C_{g}(n) as shown in FIG. 2. That is, since the delay signal A_{g}(n) is obtained by cyclically delaying the encoding signal x_{g}(n) by the delay value 0, the delay signal A_{g}(n) is the same as the encoding signal Xg(n) that is an input signal of the delay unit group 120. Since the delay signal Bg(n) is obtained by cyclically delaying the encoding signal x_{g}(n) by the delay value T/4, a signal corresponding to a last T/4 of the encoding signal x_{g}(n) is moved to the front of the encoding signal x_{g}(n). A signal corresponding to a last T/2 of the encoding signal x_{g}(n) is moved to the front of the encoding signal X_{g}(n) since the delay signal C_{g}(n) is obtained by cyclically delaying the encoding signal x_{g}(n) by the delay value T/2. Referring back to FIG. 1 , the G antenna groups 130 respectively correspond to the G space areas.
The antenna group 130 corresponding to the space area g transmits the Ng delayed encoding signal generated by the delay unit group 120 corresponding to the space area g through respective antennas 131.
A signal transmitting apparatus according to a second exemplary embodiment of the present invention will now be described with reference to FIG. 3 to FIG. 5. FIG. 3 is a diagram of the signal transmitting apparatus according to the second exemplary embodiment of the present invention.
As shown in FIG. 3, the signal transmitting apparatus according to the second exemplary embodiment of the present invention includes a plurality of spacetime channel encoders 100, an inverse fast Fourier transformer group 200, and an antenna group 300. The spacetime channel encoder 100 includes a spacetime encoder 110 and a spacetime channel delay unit 120. The spacetime channel delay unit 120 includes a plurality of phase shifter groups 121 , and the respective phase shifter groups 121 include a plurality of phase shifters 121a. The inverse fast Fourier transformer group 200 includes a plurality of inverse fast Fourier transformers (IFFT) 210, and the antenna group 300 includes a plurality of antennas 310.
Relationships between constituent elements in the signal transmitting apparatus according to the second exemplary embodiment of the present invention will now be described. For this purpose, it is assumed that the signal transmitting apparatus according to the second exemplary embodiment of the present invention transmits signals of N_{Ch}(≥ 1) channels. In addition, it is assumed that the spacetime encoder 110 of a channel i performs spacetime encoding for G^{(l) (} > 2) space areas and N^{(l) (} > 1 ) time areas.
A plurality of spacetime channel encoders 100 respectively correspond to a plurality of channels. Accordingly, the signal transmitting apparatus according to the second exemplary embodiment of the present invention includes N_{ch} spacetime channel encoders 100. Each spacetime channel encoder 100 receives a digitalmodulated symbol group from a corresponding channel, performs the spacetime encoding with respect to the plurality of space areas and at least one time area, performs phaseshifting by a plurality of phase values, and generates a plurality of phaseshifted spacetime codewords. The spacetime channel encoder 100 may vary the number of encoding space areas or the number of time areas according to a corresponding channel state. In addition, the spacetime channel encoder 100 may vary the phase value for shifting a phase or the number of phase values for shifting the phase according to a corresponding channel state. The plurality of phase shifter groups 121 respectively correspond to the plurality of space areas. Accordingly, the spacetime channel delay unit 120 of the channel i includes G^{(l)} phase shifter groups 121.
The phase shifter group 121 corresponding to the channel i (1 < i <
T)(O N_{ch}), and the space area g (1 ≤ g ≤ G^{(l)}) includes g phase shifters 121a. Therefore, the spacetime channel encoder 100 of the channel i includes
^ ^{8~}I^{l 8} phase shifters 121a. In addition, D g^{(i)} phase shifters 121a respectively correspond to s phase values.
The plurality of IFFTs 210 respectively correspond to the plurality of phase shifters 121a. Accordingly, the inverse fast Fourier transformer group 200 includes IFFTs 210 corresponding to a number NIFFT as given in Equation 2. (Equation 2)
The plurality of antennas 310 respectively correspond to a plurality of IFFTs 210. Accordingly, the antenna group 300 includes N_{A}NT(=NIFFT) antennas 310. An operation of the signal transmitting apparatus according to the second exemplary embodiment of the present invention will now be described with reference to FIG. 4. FIG. 4 is a flowchart representing the operation of the signal transmitting apparatus according to the second exemplary embodiment of the present invention. The spacetime encoder 110 of the channel i receives a signal corresponding to the channel i, performs the spacetime encoding with respect to G^{(l)} space areas and N^{(l)} time areas, and generates a spacetime codeword in step S110. In this case, the spacetime encoder 110 may receive a symbol set generated by digital modulation methods including binary phase shift keying (BPSK), quadrature amplitude modulation (QAM)), 16QAM, and 64QAM methods. In addition, the codeword is a symbol set generated by the space time encoding operation or a spacefrequency encoding operation, the symbol set generated by the spacetime encoding operation will be referred to as a spacetime codeword, and the symbol set generated by the spacefrequency encoding operation will be referred to as a spacefrequency codeword.
FIG. 5 is a diagram representing a notion of the spacetime codeword. One rectangle in FIG. 5 indicates one symbol. As shown in FIG. 5, the space time codeword is a symbol set generated by the spacetime encoder 110 with respect to the G^{(l)} space areas and the N^{(l)} time areas. Accordingly, the space time codeword of the channel i includes G^{(l)} x N^{(l)} symbols.
Referring back to FIG. 4, the spacetime encoder 110 may be an Alamouti encoder, a spacetime transmit diversity encoder, or a VBLAST encoder, but it is not limited thereto.
When the spacetime encoder 110 is the Alamouti encoder, G^{(l)} = 2, N^{(l)} = 2, and the spacetime encoder 110 generates the spacetime codeword as give in Equation 3.
(Equation 3)
That is, the spacetime encoder 110 receives two symbols s(2k) and s(2k+1), performs the spacetime encoding with respect to two space areas and two time areas, and generates four encoding symbols corresponding to the spacetime codeword. Symbols of each row in a matrix shown in Equation 3 are transmitted to different space areas, and symbols of each column are transmitted to different time areas. According to Equation 3, the Alamouti encoder outputs a symbol s(2k) for a first space area and outputs a symbol s(2k+1) for a second space area, at a time 2k. In addition, the Alamouti encoder outputs a symbol s^{*}(2k+1) for the first space area and outputs a symbol s^{*}(2k) for the second space area, at a time 2k+1.
When the spacetime encoder 110 is the spacetime transmit diversity encoder, G^{(l)} = 2, N^{(l)} = 2, and the spacetime encoder 110 generates the space time codeword as give in Equation 4.
(Equation 4)
X_{1}(Ik) X_{1}(Ik + 1) s(2k) s(2k + V) yx_{2}(2k) X_{2}(Ik + \) _{j} \ s^{*}(2k +
According to Equation 4, the spacetime transmit diversity encoder receives two symbol s(2k) and s(2k+1), performs the spacetime encoding with respect to two space areas and two time areas, and generates four encoding symbols. In addition, the spacetime transmit diversity encoder outputs the symbol s(2k) for the first space area and outputs the symbol s^{*}(2k+1) for the second space area, at the time 2k. At the time 2k+1 , the spacetime transmit diversity encoder outputs the symbol s(2k+1) for the first space area and outputs the symbol s^{*}(2k) for the second space area.
When the spacetime encoder 110 is the VBLAST encoder, G^{(i)} = 2, N^{(i)} = 1, and the spacetime encoder 110 generates the spacetime codeword as given in Equation 5.
(Equation 5)
That is, the VBLAST encoder receives the two symbols s(2k) and s(2k+1), performs the spacetime encoding with respect to two space areas and one time area, and generates two encoding symbols. Symbols of each row in a matrix shown in Equation 5 correspond to different space areas.
According to Equation 5, the VBLAST encoder outputs the symbol s(2k) for the first space area and outputs the symbol s(2k+1) for the second space time area, at the time k.
The spacetime channel delay unit 120 shifts phases of the respective symbols in the space time codeword generated by the spacetime encoder 110 by using a plurality of phase values, and generates a phaseshifted spacetime codeword in step S 120. In this case, the phaseshifted spacetime codeword is a signal that is cyclically delayed at the time area. In further detail, the phase shifter group 121 corresponding to the channel i and the space area g shifts a phase of a symbol corresponding to the space area g and a time area n among the symbols of the spacetime codeword output from the spacetime n^{(}'^{)} n« encoder 110 by using g phase values, and generates s phaseshifted symbols. That is, a g phase shifter 121a in the phase shifter group 121 of the channel i and the space area g shifts a phase of a symbol corresponding to the space area g and the time area n among the symbols of the spacetime
codeword by using a phase value ( 2π  ^{J} f^{i0} 'T s^{{i)}( ^{v}D g^{{i) J})), and generates a phaseshifted symbol. Here, f^ denotes a subcarrier corresponding to the
channel i, and τ s^{ω}( ^{y}D s^{{i)}) ^{J} denotes a time value corresponding to a channel
number (i), a number g of a space area, and a number g of a phase value. Since the phase shifter group 121 of the space area g respectively
generates s phaseshifted symbols by using a symbol corresponding to the
space area g through a time area 1 to a time area N^{w}, it generates yV^{(/)} x D s^{(l)} phaseshifted symbols. In addition, since the spacetime channel delay unit 120 includes phase shifter groups 121 of space areas 1 to G^{w}, the phase shifted spacetime codeword generated by the spacetime channel delay unit 120 includes symbols of a number given as Equation 6. (Equation 6)
FIG. 6 is a diagram representing the phaseshifted spacetime codeword generated by the spacetime channel delay unit 120. One cuboid shown in FIG. 6 is one symbol. The phaseshifted spacetime codeword in FIG. 6 is obtained when the spacetime channel encoder 100 performs the spacetime encoding with respect to four time areas and three space areas, and respectively shifts phases of symbols of first, second, and third space areas by respectively using four, two, and three phase values. The inverse Fourier transformer group 200 inverse fast Fourier transforms the plurality of phaseshifted spacetime codewords at the plurality of subcarriers corresponding to the plurality of channels in step S130. In this case, the symbols corresponding to the same space area and the same phase value among the symbols in the plurality of phaseshifted spacetime codewords are input to the same IFFT 210 so as to be inverse fast Fourier transformed at a corresponding subcarrier. In addition, the symbols corresponding to the same time area, the same phase value, and different space areas among the symbols in the phaseshifted spacetime codeword are input to the different IFFTs 210. Further, the symbols corresponding to the same space area, the same time area, and different phase values among the symbols in the phaseshifted spacetime codeword are input to the different IFFTs. The inverse Fourier transformer group 200 generates orthogonal frequency division multiplexing (OFDM) symbols that are NIFFT inverse fast Fourier transformed signals at one time area. The antenna group 300 transmits NIFFT OFDM symbols at the same time area in step S140. Accordingly, the antenna group 300 includes NIFFT antennas 310.
A signal transmitting apparatus according to a third exemplary embodiment of the present invention will now be described with reference to FIG. 7 to FIG. 10.
FIG. 7 is a diagram of the signal transmitting apparatus according to the third exemplary embodiment of the present invention. As shown in FIG. 7, the signal transmitting apparatus according to the third exemplary embodiment of the present invention includes a plurality of spacefrequency channel encoders 400, an inverse fast Fourier transformer group 500, and an antenna group 600. Each spacefrequency channel encoder 400 includes a spacefrequency encoder 410 and a spacefrequency channel delay unit 420. The spacefrequency channel delay unit 420 includes a plurality of phase shifter groups 421 , and the respective phase shifter groups 421 include a plurality of phase shifters 421a. The inverse fast Fourier transformer group 500 includes a plurality of IFFTs 510, and the antenna group 600 includes a plurality of antennas 610. Relationships between constituent elements in the signal transmitting apparatus according to the third exemplary embodiment of the present invention will now be described. For this purpose, it is assumed that the signal transmitting apparatus according to the third exemplary embodiment of the present invention transmits signals of N_{Ch}(≥ 1) channels. In addition, it is assumed that the spacefrequency encoder 410 of the channel i performs the spacetime encoding with respect to G^{(l) (} > 2) space areas and F^{(l) (}> 1) frequency areas. The plurality of spacefrequency channel encoders 400 respectively
correspond to a plurality of channels. Accordingly, the signal transmitting
apparatus according to the third exemplary embodiment of the present invention includes N_{Ch} spacefrequency channel encoders 400. The spacefrequency channel encoders 400 may vary the number of encoding space areas or the number of frequency areas according to a corresponding channel state. In addition, the spacefrequency channel encoders 400 may vary the phase value
for shifting a phase or the number of phase values for shifting the phase according to the corresponding channel state. The plurality of phase shifter groups 421 respectively correspond to the plurality of space areas. Accordingly, the spacefrequency channel delay unit 420 of the channel i includes G^{(l)} phase shifter groups 421.
The phase shifter group 421 corresponding to the channel i (1 < i <
n^{(}0 N_{ch}) and the space area g (1 ≤ g ≤ G^{1}'') includes g phase shifters 421a.
Accordingly, the spacefrequency channel encoder 400 of the channel i includes
Y D^ s^{1} phase shifters 421a. In addition, the g phase shifters 421a n(0 respectively correspond to s phase values.
The plurality of IFFTs 510 respectively correspond to a plurality of phase shifters 421a. Accordingly, the inverse fast Fourier transformer group 500
includes IFFTs 510 corresponding to the number NIFFT given as Equation 7. (Equation 7)
The plurality of antennas 610 respectively correspond to the plurality of IFFTs 510. Accordingly, the antenna group 600 includes N_{A}NT(=NIFFT) antennas 610.
An operation of the signal transmitting apparatus according to the third exemplary embodiment of the present invention will now be described with reference to FIG. 8. FIG. 8 is a flowchart representing the operation of the signal transmitting apparatus according to the third exemplary embodiment of the present invention.
The spacefrequency encoder 410 of the channel i receives a signal corresponding to the channel i, performs spacefrequency encoding with respect to G^{w} space areas and F^{(l)} frequency areas, and generates a space frequency codeword in step S210. In this case, the spacefrequency encoder 410 may receive the symbol set generated by performing the digital modulation. The spacefrequency encoder 410 may be the Alamouti encoder or the V BLAST encoder, but it is not limited thereto.
FIG. 9 is a diagram representing a notion of the spacefrequency codeword. One rectangle in FIG. 9 is one symbol. As shown in FIG. 9, the spacefrequency codeword is a symbol set generated by the spacefrequency encoder 410 with respect to G^{w} space areas and F^{(l)} frequency areas. Accordingly, the spacefrequency codeword of the channel i includes G^{(l)}x F^{(l)} symbols.
Referring back to FIG. 8, the spacefrequency channel delay unit 420 respectively shifts phases of symbols in the spacefrequency codeword generated by the spacefrequency encoder 410 by using a plurality of phase values, and generates a phaseshifted spacefrequency codeword in step S220.
In this case, the phaseshifted spacefrequency codeword is a signal that is cyclically delayed at a time area. In further detail, the phase shifter group corresponding to the channel i, and the space area g shifts a phase of a symbol corresponding to the space area g and a frequency area k among the symbols of the spacefrequency codeword output from the spacefrequency encoder 410
by using
phaseshifted symbols.That is, a D «^{{i)} phase shifter 421a in the phase shifter group 421 of the channel i and the space area g shifts the phase of the symbol corresponding to the space area g and the frequency area k among the symbols of the space
frequency codeword by using a phase value ( 2π  ^{J} f^{k(i)} τ ^{g(i)}(D ^{g{i)}) ), and
respectively generates phaseshifted symbols. Here, Jk denotes a subcarrier corresponding to the channel i and the frequency area k. Accordingly, there are F^{(l)} subcarriers corresponding to the channel i as shown in Equation 8, and the F^{(l)} subcarriers corresponding to the channel i will be referred to a subcarrier group. Equation 8 shows subcarrier groups corresponding to the channel i. (Equation 8)
s ^{v} s ^{J} denotes a time value of the channel number (i), the
number g of the space area, and the number D g^{{1)} of the phase value.
Since the phase shifter group 421 of the channel i and the space area g
generates g phaseshifted symbols by using a symbol corresponding to the space area g through the frequency area 1 to the frequency area F^{(l)}, it
_{F}U) _{χ D}d) generates s phaseshifted symbols. In addition, since the space frequency channel delay unit 420 includes phase shifter groups 421 of the space areas 1 to G^{(l)}, the phaseshifted spacefrequency codeword generated by the spacefrequency channel delay unit 420 includes symbols corresponding to a number given as Equation 9. (Equation 9)
S=^{1}FIG. 10 is a diagram representing a notion of the phaseshifted space frequency codeword generated by the spacefrequency channel delay unit 420. One cuboid shown in FIG. 10 is one symbol. The phaseshifted space frequency codeword in FIG. 10 is obtained when the spacefrequency channel encoder 400 performs the spacefrequency encoding with respect to four frequency areas and four space areas and respectively shifts phases of the symbols of first, second, third, and fourth space areas by respectively using four, two, three, and two phase values. The inverse fast Fourier transformer group 500 inverse fast Fourier transforms the plurality of phaseshifted spacefrequency codewords in the plurality of subcarrier groups respectively corresponding to the plurality of channels in step S230. In this case, the symbols corresponding to the same space area and the same phase value among the symbols in the plurality of phaseshifted spacefrequency codewords are input to the same IFFT 510 so as to be inverse fast Fourier transformed in the corresponding subcarrier group. In addition, the symbols corresponding to the same frequency area, the same phase value, and different space areas among the symbols in the plurality of phaseshifted spacefrequency codewords are input to different IFFTs 510. Further, the symbols corresponding to the same space area, the same frequency area, and different phase values among the symbols in the plurality of phaseshifted spacefrequency codewords are input to different IFFTs 510. The inverse fast Fourier transformer group 500 generates NIFFT OFDM symbols at one time area. The antenna group 600 transmits the NIFFT OFDM symbols at the same time area in step S240. Accordingly, the antenna group 600 includes NIFFT antennas 610.
A signal transmitting apparatus 700 according to a fourth exemplary embodiment of the present invention will be described with reference to FIG. 11. FIG. 11 is a diagram of the signal transmitting apparatus according to the fourth exemplary embodiment of the present invention.
The signal transmitting apparatus 700 according to the fourth exemplary embodiment of the present invention includes two spacetime channel encoders 711 and 712, a spacefrequency channel encoder 713, five IFFTs 721 to 725, and five antennas 731 to 735.
It is assumed that the spacetime channel encoder 711 corresponds to a channel 1 using fi as the subcarrier, and follows an Alamouti encoding method. Accordingly, the spacetime channel encoder 711 performs the spacetime encoding in two space areas and two time areas. The spacetime channel encoder 711 generates two phaseshifted symbols by shifting a phase of a symbol at a space area 1 by two phase values. In this case, the two generated phaseshifted symbols are respectively input to the IFFT 721 and the IFFT 722 by using fι as the subcarrier. In addition, the spacetime channel encoder 711 generates three phaseshifted symbols by shifting a phase of a symbol at a space area 2 by using three phase values. In this case, the three generated phaseshifted symbols are respectively input to the IFFT 723, the IFFT 724, and the IFFT 725 by using fi as the subcarrier. It is assumed that the spacetime channel encoder 712 corresponds to a channel 2 using f_{2} as the subcarrier, and follows the Alamouti encoding method. Accordingly, the spacetime channel encoder 712 performs spacetime encoding in two space areas and two time areas. The spacetime channel encoder 712 generates two phaseshifted symbols by shifting a phase of a symbol of the space area 1 by using two phase values. In this case, the two generated phaseshifted symbols are respectively input to the IFFT 721 and the IFFT 722 by using f_{2} as the subcarrier. In addition, the spacetime channel encoder 712 generates two phaseshifted symbols by shifting a phase of a symbol at the space area 2 by using two phase values. In this case, the two generated phaseshifted symbols are respectively input to the IFFT 723 and the IFFT 724 by using h as the subcarrier.
It is assumed that the spacefrequency channel encoder 713 corresponds to a channel 3 using f_{3} and f_{4} as the subcarrier, and follows the Alamouti encoding method. Accordingly, the spacefrequency channel encoder 713 performs the spacefrequency encoding in two space areas and two frequency areas. In this case, the two frequency areas correspond to subcarriers f_{3} and f_{4}. The spacefrequency channel encoder 713 generates six phaseshifted symbols by shifting phases of two symbols at the space area 1 by using three phase values. In this case, three phaseshifted symbols corresponding to a first frequency area among the six generated phaseshifted symbols are respectively input to the IFFTs 721 , 722, and 723 by using f_{3} as the subcarrier. In addition, three phaseshifted symbols corresponding to a second frequency area among the six generated phaseshifted symbols are respectively input to the IFFTs 721 , 722, and 723 by using f_{4} as the subcarrier.
The spacefrequency channel encoder 713 generates four phaseshifted symbols by shifting two symbols at the space area 2 by using two phase values. In this case, two phaseshifted symbols corresponding to the first frequency area among the four phaseshifted symbols are respectively input to the IFFTs 724 and 725 by using f_{3} as the subcarrier. In addition, two phaseshifted symbols corresponding to the second frequency area among the four phase shifted symbols are respectively input to the IFFTs 724 and 725 by using f_{4} as the subcarrier.
The IFFTs 721 to 725 respectively generate OFDM symbols based on the input symbols. The five antennas 731 to 735 respectively correspond to five IFFTs 721 to 725, and transmit the OFDM symbol generated by the corresponding IFFT.
The abovedescribed methods and apparatuses are not only realized by the exemplary embodiment of the present invention, but, on the contrary, are intended to be realized by a program for realizing functions corresponding to the configuration of the exemplary embodiment of the present invention or a recording medium for recording the program.
While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. [Industrial Applicability] According to the exemplary embodiments of the present invention, since the number of space areas for the encoding operation and the number of phase values for cyclic delay are adjusted, the number of antennas of the transmitting apparatus may be flexibly varied while maintaining the diversity gain. In addition, since the symbol generation apparatus according to the exemplary embodiments of the present invention spaceencodes the digital modulated symbol group and shifts the phase by using the plurality of phase values, the symbol that is spaceencoded at the frequency area may be cyclically delayed. Further, since the symbol generation apparatus according to the exemplary embodiments of the present invention adaptively varies the encoding method according to the channel state, communication quality and performance of the communication system may be improved. Still further, since the symbol generation apparatus according to the exemplary embodiments of the present invention uses different encoding methods according to the channels, data of the corresponding channel may be encoded according to channel characteristics.
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US6542556B1 (en) *  20000331  20030401  Nokia Mobile Phones Ltd.  Spacetime code for multiple antenna transmission 
KR20030038289A (en) *  20011110  20030516  삼성전자주식회사  Apparatus and method for coding/decoding of sttd in ofdm mobile communication system 
KR20060032765A (en) *  20041013  20060418  삼성전자주식회사  Apparatus and method for providing efficient transmission using block coding and cyclic delay diversities in the ofdm based cellular systems 
KR20070045893A (en) *  20051027  20070502  한국전자통신연구원  Apparatus and method for transmitting signal with multiple antennas 
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US6542556B1 (en) *  20000331  20030401  Nokia Mobile Phones Ltd.  Spacetime code for multiple antenna transmission 
KR20030038289A (en) *  20011110  20030516  삼성전자주식회사  Apparatus and method for coding/decoding of sttd in ofdm mobile communication system 
KR20060032765A (en) *  20041013  20060418  삼성전자주식회사  Apparatus and method for providing efficient transmission using block coding and cyclic delay diversities in the ofdm based cellular systems 
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