Radio transmission apparatus, radio reception apparatus and radio transmission method

A radio transmission apparatus capable of enhancing the diversity effect. In this apparatus, phase rotation section (102) performs phase rotation processing of 40.6°=26.6°+14.0°, interleavers (106,111) perform two-time interleaving processing before IQ combining processing performed in a combining section (107) and after IQ separation processing performed in an IQ separating section (108), and the original modulation symbol obtained in a mapping section (101) is thereby dispersed and mapped to/at signal points of M-ary modulation level higher two ranks or more (for example, from a QPSK symbol to 256QAM symbols).

TECHNICAL FIELD

The present invention relates to a radio transmission apparatus, radio reception apparatus and radio transmission method particularly using a modulation diversity system.

BACKGROUND ART

In recent years, attention has been drawn to multicarrier communication apparatuses using an OFDM (Orthogonal Frequency Division Multiplexing) system as apparatuses enabling high-rate radio transmission, because such communication apparatuses have resistance to multipath and fading and permit high-quality communication. Further, using modulation diversity techniques has been proposed for performing phase rotation and interleaving on modulation symbols such as QPSK (Quadrature Phase Shift Keying) and thereby enabling the diversity effect to be obtained.

Modulation diversity is described in Non-patent Document 1, for example. Referring toFIG. 1, modulation diversity will be described briefly.FIG. 1shows a case of using QPSK (Quadrature Phase Shift Keying) as a modulation scheme as an example. First, a transmitting side rotates a phase of a symbol mapped on the IQ plane by a predetermined angle. Next, the transmitting side performs interleaving on an I (in-phase) component and Q (quadrature) component using uniform or random interleavers respectively for the I component and Q component. By this means, signals subjected to inverse fast Fourier transform (IFFT) are processed such that the I component and Q component of the symbol prior to interleaving are mapped to different subcarriers. InFIG. 1, the I component is mapped to a subcarrier B, while the Q component is mapped to a subcarrier A.

First, a receiving side performs fast Fourier transform (FFT), and thereby extracts the I component and Q component multiplexed on the subcarriers. Next, the receiving side performs deinterleaving, and thereby restores the I component and Q component to original arrangements. Then, the receiving side performs demapping processing based on a constellation of the restored I component and Q component, and thereby obtains reception data.

Here, assuming that the subcarrier A has a good channel state and that the subcarrier B has a poor channel state, the receiving side obtains a constellation distorted in the Q-component direction as shown inFIG. 1. By this means, it is possible to maintain a signal point distance on the constellation at a relatively long, and to restore bits in a packet accurately averagely at a demapping. Thus, in modulation diversity, even when the fading variation occurs on each subcarrier due to multipath fading, the same effect can be obtained as in dispersing a SNR (Signal-to-Noise Ratio) in the subcarrier direction to make a correction. As a result, the modulation symbol undergoes the variation as if the signal is transmitted on an AWGN (Additive White Gaussian Noise) communication path, and the diversity gain can thus be obtained.

FIG. 2illustrates a configuration of multicarrier transmission apparatus10that performs modulation diversity transmission processing.FIG. 3illustrates a configuration of multicarrier reception apparatus30that receives and demodulates signals from the apparatus10.

Multicarrier transmission apparatus10has modulation diversity modulation section11, and inputs transmission data to mapping section12in modulation diversity modulation section11. Mapping section12maps the transmission data on symbols on the IQ plane corresponding to a modulation scheme such as BPSK, QPSK, 16QAM and the like.

Phase rotation section13rotates the phase of a mapped symbol by a predetermined angle. IQ separating section14separates the symbol with the phase rotated into the I component and Q component. The separated I and Q components are temporarily stored respectively in buffers15and16. The Q component stored in buffer16is interleaved in interleaver17and output to combining section18. In addition, althoughFIG. 2illustrates the case of interleaving the Q component, the I component may be subjected to interleaving processing, or both the I and Q components may be subjected to interleaving processing.

Combining section18combines the I component output from buffer15and the Q component output from interleaver17to place back in a constellation. A modulation diversity symbol is thereby obtained. The modulation diversity symbol is multiplexed on a predetermined subcarrier in serial/parallel transform (S/P) section19and inverse fast Fourier transform (IFFT) section20. In other words, serial/parallel transform (S/P) section19and inverse fast Fourier transform (IFFT) section20map the modulation diversity symbol to any one of a plurality of subcarriers orthogonal to one another, and sequentially modulate each of the subcarrier with the modulation diversity symbol.

Thus, in multicarrier transmission apparatus10, since interleaver17interleaves the Q component, the I component is fixed to some subcarrier, while a subcarrier to which the Q component is mapped varies according to interleaving patterns. An IFFT-processed signal is subjected to radio transmission processing such as analog/digital conversion processing, upconverting and the like in radio transmission section21, and then transmitted via antenna22.

Multicarrier reception apparatus30that receives and demodulates signals transmitted from multicarrier transmission apparatus10has modulation diversity demodulation section31. In multicarrier reception apparatus30, radio reception section33performs radio reception processing such as downconverting, analog/digital conversion processing and the like on a radio signal received in antenna32to output to fast Fourier transform (FFT) section34. FFT section34extracts a modulation diversity symbol multiplexed on each subcarrier. Phase compensation section35compensates the extracted modulation diversity symbol for a phase variation occurring during propagation. The phase-compensated modulation diversity symbol is output to IQ separating section36inmodulation diversity demodulation section31.

IQ separating section36separates symbols into the I component and Q component. Of the separated components, IQ separating section36outputs one component that is not interleaved at the transmitting side to combining section40via buffer37without any processing, while outputting the other component interleaved at the transmitting side to deinterleaver39via buffer38. Deinterleaver39performs processing inverse to that in interleaver17, and thereby restores interleaved components to an original arrangement and outputs to combining section40. As a result, combining section40obtains a symbol comprised of the original pair of I component and Q component.

Phase rotation section41rotates the phase of the combined symbol in the inverse direction by the same angle to/as in phase rotation section13of the transmitting side. Demapping section42demaps the phase-rotated symbol and thereby outputs reception data.

Here,FIG. 4illustrates modulation symbols that are subjected to QPSK modulation in mapping section12and then phase rotation processing of 26.6° in phase rotation section13. As can be seen fromFIG. 4, the modulation symbols are mapped at points of 16QAM at an angle of 26.6 degrees.

FIG. 5illustrates I components and Q components combined in combining section18. InFIG. 5, numerals “1” to “4” denote respective numbers of four QPSK symbols. I components are not interleaved, and therefore, the I components of modulation symbols are input to combining section18in the same order. In contrast thereto, the order of the Q components is rearranged by interleaving and input to combining section18.

Here, four modulated symbols in mapping section12are expressed as S0=[S10S20S30S40]=[(1 1), (−1 1), (1 −1), (−1−1)], where numerical subscripts “1” to “4” respectively represent four symbols obtained by QPSK, and a numerical superscript “0” represents a transmission symbol. Then, for example, using the I component and Q component, symbol1is represented as S10=(S1I0, S1Q0).

Assuming that the interleaving pattern as shown inFIG. 5is used at the transmitting side, since an original first symbol is transmitted in the received first symbol and second symbol, to obtain the original first symbol, the receiving side separates the received symbols into I components and Q components, deinterleaves the Q components, and obtains the original first symbol by combining. Here,FIG. 6shows a constellation in the case of obtaining an original one symbol by combining when a received symbol is represented as Sr1=[S1r1, S2r1, S3r1, S4r1] (where numerical subscripts “1” to “4” respectively represent different symbols, and a numerical superscript “r1” represents a received symbol.) Four points inFIG. 6are candidates for reception points. In addition, although inFIG. 6, length of |S1Ir1| and |S2Qr1| are shown with almost the same, the lengths are actually different from each other due to the difference in fading and the like imposed on the symbol and four points in the figure form a parallelogram.

Thus, it is a feature of the modulation diversity system to transmit components of an original symbol in different symbols and to avoid the both components of symbol restored at the receiving side becoming smaller. Particularly, when this system is used in OFDM, it is possible to obtain large diversity gains because each subcarrier undergoes different fading.

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

In modulation diversity as described above, when either of I and Q components of an original symbol maintains its gain to some extent, the possibility is high that the original data is demodulated properly. For example, as shown inFIG. 5, under circumstances where the I component of symbol1is mapped at subcarrier1and its Q component is mapped at subcarrier2, even when the channel quality of subcarrier1is poor and the channel quality of subcarrier2is good, it is possible to reduce the error in decision on symbol1. Similarly, with respect to symbol2, when either channel quality of subcarrier2mapped the I component and subcarrier3mapped the Q component is good, it is possible to reduce the error in decision on symbol2.

However, when the both channel qualities are poor in subcarriers1and2, the decision error of symbol1becomes large. Similarly, when the both channel qualities are poor in subcarriers2and3, the decision error of symbol2becomes large.

It is an object of the present invention to provide a radio transmission apparatus and radio transmission method enabling the diversity effect to be further enhanced in performing the modulation diversity transmission processing.

Means for Solving the Problem

In the present invention, in performing the modulation diversity processing, phase rotation processing is performed such that an original symbol is mapped at a signal point of a higher modulation level by two ranks or more, and interleaving processing is performed on the I component and/or Q component a plurality of times.

A radio transmission apparatus of the present invention adopts a configuration provided with a phase rotator which rotates a phase of a modulation symbol and maps a signal point of the modulation symbol at a signal point of an M-ary modulation level higher by two ranks or more, and a plurality of interleavers that performs interleaving processing a plurality of times on the I component and/or Q component of the modulation symbol with the phase rotated.

According to this configuration, the original modulation symbol is mapped at symbols of the higher modulation level by two ranks or more to be dispersed, and it is thereby possible to enhance the diversity effect. For example, when the original modulation symbol is a QPSK symbol, the original symbol is dispersed and mapped to/at symbols of the modulation level of 256QAM or more.

A radio transmission apparatus of the invention adopts a configuration provided with a modulator that maps transmission data on a modulation symbol comprised of an I component and a Q component, a phase rotator that rotates a phase of the modulation symbol by a predetermined angle and maps a signal point of the modulation symbol at a signal point of an M-ary modulation level higher by two-rank, a first IQ separator that separates the modulation symbol with the phase rotated to the I component and the Q component with reference to an IQ axis rotated a predetermined angle, a first interleaver that interleaves the I component and/or the Q component separated in the first IQ separator, a first IQ combiner that combines the I component and the Q component output from the first interleaver, a second IQ separator that separates the modulation symbol obtained in the first IQ combiner into the I component and the Q component, a second interleaver that interleaves the I component and/or the Q component separated in the second IQ separator, a second IQ combiner that combines the I component and the Q component output from the second interleaver, and a transmitter that transmits the symbol obtained in the second IQ combiner.

According to this configuration, first, the phase rotator maps an original modulation symbol at a signal point of a two-rank higher modulation level. In other words, when the modulation symbol is of QPSK, the symbol is mapped on 256QAM while being inclined a predetermined angle. Next, the first IQ separator separates the QPSK symbol existing on 16QAM inclined a predetermined angle on 256QAM into an I component and Q component, the component(s) is interleaved in the first interleaver, both components are combined in the first IQ combiner, and the original QPSK symbol is thus dispersed on 16QAM inclined the predetermined angle on 256QAM. The IQ components separated in the second IQ separator are interleaved in the second interleaver, both components are combined in the second IQ combiner, and the original QPSK symbol is thus dispersed on 256QAM. As a result, the original modulation symbol is dispersed and mapped to/at signal points of the two-rank higher modulation level, and it is thus possible to obtain the significant diversity effect. For example, a QPSK symbol is capable of obtaining the diversity gain of maximum four symbols as compared with conventional modulation diversity that obtains the diversity gain of two symbols.

A radio transmission apparatus of the invention adopts a configuration provided with a modulator that maps transmission data on a modulation symbol comprised of an I component and a Q component, a first phase rotator that rotates a phase of the modulation symbol by a predetermined angle and maps a signal point of the modulation symbol at a signal point of a one-rank higher M-ary modulation level, a first IQ separator that separates the modulation symbol with the phase rotated to the I component and the Q component, a first interleaver that interleaves the I component and/or the Q component separated in the first IQ separator, a first IQ combiner that combines the I component and the Q component output from the first interleaver, a second phase rotator that rotates a phase of the modulation symbol obtained in the first IQ combiner by a predetermined angle and maps a signal point of the modulation symbol at a signal point of a one-rank higher M-ary modulation level, a second IQ separator that separates the modulation symbol with the phase rotated into the I component and the Q component, a second interleaver that interleaves the I component and/or the Q component separated in the second IQ separator, a second IQ combiner that combines the I component and the Q component output from the second interleaver, and a transmitter that transmits the symbol obtained in the second IQ combiner.

According to this configuration, first, the first phase rotator maps an original modulation symbol at a signal point of a one-rank higher modulation level. In other words, when the modulation symbol is of QPSK, the symbol is mapped on 16QAM while being inclined a predetermined angle. Next, the I component and/or Q component separated in the first IQ separator is interleaved in the first interleaver, both components are combined in the first IQ combiner, and the original QPSK symbol is thus dispersed on 16QAM. Next, the second phase rotator maps the 16QAM-symbol at a signal point of a one-rank higher modulation level. In other words, the 16QAM-symbol is mapped on 256QAM while being inclined a predetermined angle. Next, the I component and/or Q component separated in the second IQ separator is interleaved in the second interleaver, both components are combined in the second IQ combiner, and the original QPSK symbol is thus dispersed on 256QAM. As a result, the original modulation symbol is dispersed and mapped to/at signal points of a two-rank higher modulation level, and it is thus possible to obtain the significant diversity effect. For example, a QPSK symbol is capable of obtaining the diversity gain of maximum four symbols as compared with conventional modulation diversity that obtains the diversity gain of two symbols.

The radio transmission apparatus of the invention adopts a configuration where the modulator performs QPSK modulation, the phase rotator rotates the phase by 26.6°+14.0°, and the first IQ separator separates into the I component and the Q component with reference to the IQ axis inclined 14.0°.

According to this configuration, it is possible to obtain 256QAM modulation diversity symbols from a QPSK symbol.

The radio transmission apparatus of the invention adopts a configuration where the modulator performs BPSK modulation, the phase rotator rotates the phase by 45.0°+26.6°, and the first IQ separator separates into the I component and the Q component with reference to the IQ axis inclined 26.6°.

According to this configuration, it is possible to obtain 16QAM modulation diversity symbols from a BPSK symbol.

The radio transmission apparatus of the invention adopts a configuration where the modulator performs QPSK modulation, the first phase rotator rotates the phase by 26.6°, and the second phase rotator rotates the phase by 14.0°.

According to this configuration, it is possible to obtain256QAM modulation diversity symbols from a QPSK symbol.

The radio transmission apparatus of the invention adopts a configuration where the modulator performs BPSK modulation, the first phase rotator rotates the phase by 45.0°, and the second phase rotator rotates the phase by 26.6°.

According to this configuration, it is possible to obtain 16QAM modulation diversity symbols from a BPSK symbol.

The radio transmission apparatus of the invention adopts a configuration where the transmitter maps the symbol obtained in the second IQ combiner to one of a plurality of subcarriers orthogonal to each other, and thereby modulates each of the subcarriers with the mapped symbol to transmit.

According to this configuration, an original symbol is dispersed to symbols of a higher modulation level by two ranks or more by modulation diversity of the invention, the symbols are dispersed to a plurality of subcarriers and transmitted, and it is thus possible to enhance the probability that the original symbol is transmitted without error even when some subcarrier has poor channel quality.

A radio reception apparatus of the invention adopts a configuration provided with an IQ separator that separates a received signal into an I component and a Q component, a deinterleaver that performs deinterleaving processing on the separated I component and/or Q component, an IQ combiner that combines deinterleaved components, a phase rotator that rotates a phase of a symbol combined in the IQ combiner by a predetermined angle, an LLR combiner that calculates log-likelihood ratio (LLR) for each bit in the symbol with the phase rotated, separates a value of LLR for each bit into an I component and a Q component, performs deinterleaving processing on a value of LLR for each bit of the I component and/or the Q component, and combines values of LLR of the I component and the Q component subjected to deinterleaving, and a demodulator that demaps the LLR-combined symbol to obtain reception data.

According to this configuration, a symbol of a higher modulation level by one rank than that of an original modulation symbol, that is obtained in the IQ combiner, undergoes different fading for each symbol, and therefore, the constellation is not a square. However, the LLR combiner performs LLR combining using the value of LLR for each bit in the symbol, and thereby combines information of the I component and Q component of the original symbol, the symbol is then demodulated, and it is thus possible to restore and demodulate the original symbol with excellence.

Advantageous Effect of the Invention

According to the invention, it is possible to improve the diversity effect.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention will specifically be described below with reference to accompanying drawings.

FIG. 7illustrates a configuration of a multicarrier transmission apparatus to which the present invention is applied. Multicarrier transmission apparatus100inputs transmission data to mapping section101as modulation means. Mapping section101performs QPSK modulation, and thereby maps transmission data on either one of four signal points on the IQ plane.

Phase rotation section102rotates the phase of the mapped symbol by 40.6° (26.6°+14.0°=40.6°). By this means, as shown inFIG. 8, four QPSK symbols are mapped on 256QAM symbols while being inclined 40.6°.

The phase-rotated symbol is separated into an I component and Q component in IQ separating section103. Here, IQ separating section103separates the symbol with reference to an IQ axis inclined 14.0° from the original IQ axis. More specifically, the IQ separating section103inclines the ordinary IQ axis as shown inFIG. 8by 14.0°, and separates the I component and Q component relative to the inclined IQ axis (which is referred to as deformed IQ separation).

The separated I component and Q component are temporarily stored in buffers104and105respectively. Q components stored in buffer105are interleaved in interleaver106, and output to combining section107.

FIG. 9illustrates I components and Q components when combined in combining section107. Numerals “1” to “4” denote numbers of four QPSK symbols. Since I components are not interleaved, I components of modulation symbols are input to combining section107with the original order. In contrast thereto, the order of Q components of modulation symbols is changed by interleaving, and the rearranged Q components are input to combining section107.

Combining section107combines the I component output from buffer104and the Q component output from interleaver106to place back in a constellation. The combined symbols output from combining section107thus have a constellation of 16QAM inclined 26.6° from the IQ axis. The symbols obtained by combining are output to IQ separating section108.

IQ separating section108separates the input symbol into an I component and Q component. Here, IQ separating section108performs general IQ separation, instead of deformed IQ separation, which differs from IQ separating section103as described above. Separated I component and Q component are temporarily stored in buffers109and110respectively. Q components stored in buffer110undergo second interleaving processing in interleaver111and are output to combining section112.

FIG. 11illustrates I components and Q components when combined in combining section112. Here, as an interleaving pattern of interleaver111, it is assumed that such a pattern is set that a first input signal is output third, a second input signal is output first, a third input signal is output fourth, and that a fourth input signal is output second. In addition, as an interleaving pattern of the above-mentioned first interleaver106, as can be seen fromFIG. 9, such a pattern is set that a first input signal is output second, a second input signal is output third, a third input signal is output fourth, and that a fourth input signal is output first.

Numerals “1” to “4” denote numbers of four QPSK symbols inFIG. 11. Here, when a signal subjected to first interleaving (i.e. the signal prior to combining in combining section107) is represented as S1=[(S1I0, S4Q0), (S2I0, S1Q0), (S3I0, S2Q0), (S4I0, S3Q0)], a signal subjected to second interleaving (i.e. the signal prior to combining in combining section112) can be represented as S2=[(S1I0, S2Q1), ( S2I1, S4Q1), ( S3I1, S1Q1), (S4I1, S3Q1)]. At this point, as can be seen fromFIG. 11, for example, S1I1has components of original QPSK symbols1and4. Similarly, S2Q1has components of original QPSK symbols2and1.

In addition, in the above-mentioned representation, numerical subscripts “1” to “4” respectively represent four symbols obtained in QPSK, a numerical superscript “0” represents a transmission symbol, and a numerical superscript “1” represents a signal subjected to the first interleaving processing. For example, symbol1subjected to mapping processing in mapping section101is represented as S10=(S1I0, S1Q0) using the I component and Q component.

Combining section112combines I component output from buffer109and Q component output from interleaver111to place back in a constellation. Combined symbols output from combining section112thus have a constellation of 256QAM as shown inFIG. 12. In this way, modulation diversity symbols are obtained which are subjected to modulation diversity processing twice.

The modulation diversity symbols are multiplexed on predetermined subcarriers in serial/parallel transform (S/P) section113and inverse fast Fourier transform (IFFT) section114. In other words, serial/parallel transform (S/P) section113and inverse fast Fourier transform (IFFT) section114map the modulation diversity symbol to any one of a plurality of subcarriers orthogonal to one another, and sequentially modulates each of the subcarriers with the modulation diversity symbol. The IFFT-processed signal is subjected to radio transmission processing such as analog/digital conversion processing, upconverting and the like in radio transmission section115, and transmitted via antenna116.

The operation and effect of multicarrier transmission apparatus100of this Embodiment will be described below. In multicarrier transmission apparatus100, as described above, phase rotation section102performs phase rotation processing of 40.6°=26.6°+14.0°, the interleaving processing is performed twice, before the IQ combining processing performed in combining section107and after the IQ separation processing performed in IQ separating section108, and IQ components of QPSK symbols are thereby dispersed and mapped to/at signal points of 256QAM. As a result, a QPSK symbol is capable of obtaining the diversity gain of maximum four symbols as compared with conventional modulation diversity that obtains the diversity gain of two symbols.

For example, as shown inFIG. 11, subcarrier1is mapped components of three symbols except the third QPSK symbol, subcarriers2and3are mapped components of all the four symbols, and subcarrier4is mapped components of three symbols except the first QPSK symbol. As compared with the conventional modulation diversity system where each subcarrier is mapped components of only two symbols as shown inFIG. 5, it is understood that the diversity effect is significantly improved.

For example, in this Embodiment, if subcarrier2has good channel quality, even when subcarries except subcarrier2have poor channel quality, it is possible to maintain decision error characteristics of all the symbols at a certain level or more since subcarrier2contains components of all the four symbols. In contrast thereto, in conventional modulation diversity as shown inFIG. 5, if subcarries except subcarrier2have poor channel quality even when subcarrier2has good channel quality, although it is possible to maintain decision error characteristics of two symbols,1and2, at a certain level or more, it is not possible to maintain decision error characteristics of two symbols,3and4.

Thus, according to this Embodiment, phase rotation section102performs the phase rotation processing of 40.6°=26.6°+14.0° and the interleaving processing is performed twice before the IQ combining processing performed in combining section107and after the IQ separation processing performed IQ separating section108. And therefore, it is possible to implement multicarrier transmission apparatus100with the modulation diversity effect improved.

FIG. 13illustrates a multicarrier transmission apparatus of this Embodiment with corresponding portions inFIG. 7assigned the same reference numerals. Multicarrier transmission apparatus200has the same configuration as that of multicarrier transmission apparatus100except that configurations of phase rotation section201and IQ separating section202are different and that the apparatus200has phase rotation section203.

Phase rotation section201rotates the phase of the mapped QPSK symbol by 26.6°. By this means, as shown inFIG. 4, four QPSK symbols are mapped on 16QAM symbols while being inclined 26.6°.

IQ separating section202performs general IQ separation, although IQ separating section103performs deformed IQ separation in Embodiment 1. In other words, in multicarrier transmission apparatus200, the processing up to combining section107is performed in the same way as in conventional modulation diversity.

Phase rotation section203rotates the phase of the symbol output from combining section107by 14.0°. By this means, as shown inFIG. 10, 16QAM symbols are mapped at signal points of 256QAM while being inclined 14.0°. The subsequent processing is the same as in Embodiment 1.

In other words, in Embodiment 1, phase rotation section102performs the phase rotation processing of 40.6°=26.6°+14.0°, QPSK symbols are thereby mapped at signal points of 256QAM one time while being inclined, and IQ separating section103performs the deformed IQ separation. In contrast thereto, in this Embodiment, two phase rotation sections,201and203, are provided to map QPSK symbols on 16QAM and then on 256QAM successively at an angel of predetermined degrees, and the symbols are subjected to the interleaving processing.

Thus, this Embodiment are provided with first phase rotation section201that rotates the phase of a modulation symbol by 26.6°, first IQ separating section202, first interleaver106, first IQ combining section107, second phase rotation section203that rotates the symbol obtained by combining by 14.0°, second IQ separating section108, second interleaver111, second IQ combining section112, and a transmitting section that transmits the symbol obtained in second IQ combining section112, and it is thereby possible to implement multicarrier transmission apparatus200with the modulation diversity effect improved, as in Embodiment 1.

This Embodiment proposes a multicarrier reception apparatus that receives and demodulates signals from the multicarrier transmission apparatus as described in Embodiments 1 and 2.FIG. 14illustrates a configuration of the multicarrier reception apparatus of this Embodiment.

In multicarrier reception apparatus300, radio reception section302subject a radio signal received in antenna301to radio reception processing such as downconverting, analog/digital conversion processing and the like and output to fast Fourier transform (FFT) section303. FFT section303extracts modulation diversity symbols multiplexed on each subcarrier. Phase compensating section304compensates the extracted modulation diversity symbol for a phase variation developed during propagation. The phase-compensated modulation diversity symbol is output to IQ separating section305.

IQ separating section305separates each symbol into an I component and a Q component. Of the separated components, IQ separating section305outputs the I component to combining section309via buffer306without any processing, while outputting the Q component to deinterleaver308via buffer307. Deinterleaver308performs processing inverse to that in interleaver111(FIGS. 7 and 13), and thereby restores Q components interleaved in second interleaving to an original arrangement and outputs to combining section309. Consequently, combining section309forms symbols of 16QAM as a result of combining. An output of combining section309is output to phase rotation section310.

Phase rotation section310rotates the phase of the input 16QAM symbol by −14.0°. The 16QAM symbol is output to LLR calculating section312in LLR combining section330.

LLR calculating section312calculates values of Log Likelihood Ratio (LLR) of four bits of the input 16QAM symbol, and outputs the values of LLR to separating section311. The processing in LLR calculating section312will specifically be described below. 16QAM symbols input to LLR calculating section312are explained in a following example. Here, when it is assumed that data of QPSK (data of mapping section101) is (0,0), (1,0), (0,1) and (1,1) and that an interleaving pattern as shown inFIG. 9is used, an output subsequent to modulation diversity combining is of some point expressed in a constellation as shown inFIG. 15. When the interleaving pattern as shown inFIG. 9is used, a first symbol is (0,0,1,1), a second symbol is (1,0,0,0), a third symbol is (0,1,1,0), and a fourth symbol is (1,1,0,1).

LLR calculating section312calculates LLR for each bit. LLR calculation of the first symbol is considered.FIG. 16illustrates LLR calculation for each bit. InFIG. 16, o represents a candidate point for “0” or “1”, and ● represents a reception point. As can be seen from the figure, with respect to the first bit and second bit, a value (“1” or “0”) of the bit is obtained by placing a candidate point in the I-axis direction and performing LLR calculation between the reception point and candidate point. With respect to the third bit and fourth bit, a value of the bit is obtained by placing a candidate point in the Q-axis direction and performing LLR calculation between the reception point and candidate point. As is well known, as shown inFIG. 17, LLR calculation is performed as expressed in the following equation, where a noise probability density is P, a distance from the origin to a candidate point for “0” is A, a distance from the origin to a candidate point for “1” is −A, a reception point is x, and noise dispersion is σ2:

Here, the first bit is paired with the third bit, and the second bit is paired with the fourth bit. Therefore, after separating section311separates values of LLR of bits, the third bit and fourth bit are deinterleaved in deinterleavers317and318respectively, and the first bit and deinterleaved third bit are combined in combining section319, while the second bit and deinterleaved fourth bit are combined in combining section320. QPSK symbols are thus obtained, the QPSK symbols undergo demapping in demapping section321, and reception data is obtained.

The operation and effect of multicarrier reception apparatus300of this Embodiment will be described below. Multicarrier reception apparatus300first performs the same demodulation processing as in demodulation in conventional modulation diversity in IQ separating section305, deinterleaver308and combining section309, and thereby forms 16QAM symbols.

At this point, since different fading is imposed on each symbol, the constellation is not of a square. Therefore, it is not possible to perform second demodulation processing by the same demodulation processing as the conventional processing. Thus, in multicarrier reception apparatus300, LLR calculating section312calculates likelihood for each bit, and separating section311separates the likelihood for each bit. Then, performing LLR combining processing obtains I components and Q components of original modulation symbols (QPSK symbols in this Embodiment). It is thereby possible to restore original modulation symbols from symbols that are performed the modulation diversity processing a plurality of times and transmitted from the transmitting side.

Thus, according to this Embodiment, providing LLR combining section330makes it possible to excellently restore original modulation symbols from received signals subjected to the plurality-of-time modulation diversity processing and demodulate the received signals.

In addition, although each of the above-mentioned Embodiments describes the case of interleaving Q components, I components may be interleaved, or both of I components and Q components may be interleaved.

Further, above-mentioned Embodiment 1 describes the case where mapping section101performs QPSK modulation processing, phase rotation section102rotates the phase by 26.6°+14.0°, IQ separating section103separates the I component and the Q component with reference to the IQ axis inclined 14.0°, and 256QAM modulation diversity symbols are thus obtained from QPSK symbols. However, the invention is not limited to such a case. When mapping section101performs BPSK modulation processing, phase rotation section102rotates the phase by 45.0°+26.6°, and IQ separating section103separates the I component and the Q component with reference to the IQ axis inclined 26.6°, it is possible to obtain 16QAM modulation diversity symbols from BPSK symbols.

Similarly, above-mentioned Embodiment 2 describes the case where mapping section101performs QPSK modulation processing, phase rotation section201rotates the phase by 26.6°, while phase rotation section203rotates the phase by 14.4°, and 256QAM modulation diversity symbols are thus obtained from QPSK symbols. However, the present invention is not limited to such a case. When mapping section101performs BPSK modulation processing, and phase rotation section201rotates the phase by 45.0°, while phase rotation section203rotates the phase by 26.6°, it is possible to obtain 16QAM modulation diversity symbols from BPSK symbols.

Further, each of the above-mentioned Embodiments describes specific numeric values as phase rotation angles. With respect to modulation schemes such as BPSK, QPSK, 16QAM, 64QAM and the like with an even-numbered M-ary number, the phase rotation angle in each modulation scheme to perform modulation diversity modulation is expressed in the following equation generally.
tan(θ)=1/n(nis a modulation level)  (2)

Accordingly, in the present invention, when an original modulation symbol is mapped at a signal point of a higher modulation level by two ranks or more, the phase rotation processing is performed in consideration of equation (2). In addition, angles 26.6° and 14.0° used in the above-described embodiments are values meeting tan(θ)=½ and tan(θ)=¼ respectively, and both angles are values conforming to equation.(2).

Further, each of the above-mentioned Embodiments describes the case where the present invention is applied to multicarrier transmission apparatuses100and200, but the invention is not limited to the multicarrier transmission apparatus, and is widely applied to cases of performing the modulation diversity processing.

Each function block employed in the description of each of the aforementioned embodiments may typically be implemented as an LSI constituted by an integrated circuit. These may be individual chips or partially or totally contained on a single chip.

“LSI” is adopted here but this may also be referred to as “IC”, “system LSI”, “super LSI”, or “ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. After LSI manufacture, utilization of an FPGA (Field Programmable Gate Array) or a reconfigurable processor where connections and settings of circuit cells within an LSI can be reconfigured is also possible.

The present application is based on Japanese Patent Application No.2003-341653 filed on Sep. 30, 2003, entire content of which is expressly incorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in radio communication systems requiring further improvements in modulation diversity effect such as OFDM communication, for example.