# Patent

## Title
Radio communication method, radio transmitting apparatus, and radio receiving apparatus

## Abstract

A duplicating section 11 duplicates a bit sequence to be input, and a 16QAM section 121 modulates a bit sequence of a duplicating source to form a symbol, a 16QAM section 122 modulates the duplicated bit sequence to form a symbol, an S/P section 13 parallel converts the symbol sequence input in series, an S/P section 14 parallel converts the symbol sequence input in series, and an IFFT section 15 provides IFFT processing to the input symbol sequence. Since each of multiple same bits duplicated by the duplicating section 11 is included in a different symbol, each of the multiple same bits is allocated to each of multiple subcarriers each having a different frequency by IFFT processing. As a result, a multicarrier signal including the multiple same bits each having a different frequency is generated.

## Background
TECHNICAL FIELD
The present invention relates to a radio communication method, radio transmitting apparatus and radio receiving apparatus.
BACKGROUND ART
Conventionally, in radio communications, to improve reception quality, there are performed an antenna diversity transmission that switches an antenna to transmit the same signal and an automatic repeat request that retransmits a signal according to a request from a receiving side when an error occurs in the signal. However, in the antenna diversity transmission, since multiple antennas must be prepared, an apparatus scale on a transmitting side will be increased. Additionally, in the automatic repeat request, the frequency of retransmission will increase as an error rate is high, resulting in a reduction transmission efficiency.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a radio communication method, radio transmitting apparatus and radio receiving apparatus that is capable of improving reception quality without performing transmission and retransmission using a plurality of antennas.
In order to attain the above object, the present invention transmits a multicarrier signal including a plurality of same bits each having a different frequency.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram illustrating a configuration of a radio transmitting apparatus according to Embodiment 1 of the present invention;
FIG. 2 is a block diagram illustrating a configuration of a radio receiving apparatus according to Embodiment 1 of the present invention;
FIG. 3 is a view illustrating a mapping of each symbol in QPSK modulation;
FIG. 4 is a view illustrating a mapping of each symbol in 16QAM modulation;
FIG. 5 is a view illustrating a corresponding relationship between a subcarrier and a transmission bit in QPSK modulation;
FIG. 6 is a view illustrating a corresponding relationship between a subcarrier and a transmission bit according to Embodiment 1 of the present invention;
FIG. 7 is a view illustrating fading variation;
FIG. 8 is a view illustrating an error rate characteristic;
FIG. 9 is a view illustrating fading variation;
FIG. 10 is a block diagram illustrating a configuration of a radio transmitting apparatus according to Embodiment 2 of the present invention;
FIG. 11 is a block diagram illustrating a configuration of a radio receiving apparatus according to Embodiment 2 of the present invention;
FIG. 12 is a view illustrating a corresponding relationship between a subcarrier and a transmission bit according to Embodiment 2 of the present invention;
FIG. 13 is a view illustrating a corresponding relationship between a subcarrier and a transmission bit according to Embodiment 2 of the present invention;
FIG. 14 is a view illustrating a corresponding relationship between a subcarrier and a transmission bit according to Embodiment 2 of the present invention;
FIG. 15 is a block diagram illustrating a configuration of a radio transmitting apparatus according to Embodiment 3 of the present invention;
FIG. 16 is a block diagram illustrating a configuration of a radio receiving apparatus according to Embodiment 3 of the present invention;
FIG. 17 is a view illustrating a corresponding relationship between a subcarrier and a transmission bit according to Embodiment 3 of the present invention;
FIG. 18 is a view illustrating a corresponding relationship between a subcarrier and a transmission bit according to Embodiment 3 of the present invention;
FIG. 19 is a block diagram illustrating a configuration of a radio transmitting apparatus according to Embodiment 4 of the present invention;
FIG. 20 is a view illustrating a mapping pattern according to Embodiment 4 of the present invention;
FIG. 21 is a view illustrating a mapping pattern according to Embodiment 4 of the present invention;
FIG. 22 is a view illustrating a corresponding relationship between a subcarrier and a transmission bit according to Embodiment 4 of the present invention;
FIG. 23 is a block diagram illustrating a configuration of a radio receiving apparatus according to Embodiment 4 of the present invention; and
FIG. 24 is a view illustrating a combining method according to Embodiment 4 of the present invention.



BEST MODE FOR CARRYING OUT THE INVENTION
The following will specifically explain embodiments of the present invention with reference to the drawings.
Embodiment 1
FIG. 1 is a block diagram illustrating a configuration of a radio transmitting apparatus according to Embodiment 1 of the present invention. The radio transmitting apparatus illustrated in FIG. 1 includes a duplicating section 11, a modulating section 12 having a 16QAM section 121 and a 16QAM section 122, an S/P section 13, an S/P section 14, an IFFT section 15, a transmission RF section 16, and an antenna 17, and transmits a multicarrier signal including multiple same bits each having a different frequency.
The duplicating section 11 duplicates a bit sequence to be input. This duplicates the same bit to generate multiple same bits. The bit sequence of the duplicating source is input to the 16QAM section 121 and the duplicated bit sequence is input to the 16QAM section 122.
The 16QAM section 121 modulates the bit sequence of the duplicating source by use of 16QAM modulation scheme to form a symbol. Further, the 16QAM section 122 modulates the duplicated bit sequence by use of 16QAM modulation scheme to form a symbol. As a result, the multiple same bits are included in each different symbol.
The S/P section 13 parallel converts a symbol sequence input in series from the 16QAM section 121, and inputs it to the IFFT section 15. Furthermore, the S/P section 14 parallel converts a symbol sequence input in series from the 16QAM section 122, and inputs it to the IFFT section 15.
The IFFT section 15 provides IFFT (Inverse Fast Fourier Transform) processing to the input symbol sequences. This generates a multicarrier signal in which each of the multiple symbols input from the S/P section 13 and the S/P section 14 is allocated to each of multiple subcarriers each having a different frequency. Since each of the multiple same bits duplicated by the duplicating section 11 is included in the different symbol, each of the multiple same bits is allocated to each of the multiple subcarriers each having a different frequency by this IFFT processing. As a result, a multicarrier signal including the multiple same bits each having a different frequency is generated.
Since an OFDM (Orthogonal Frequency Division Multiplexing) system is used as a multicarrier system herein, IFFT processing is performed. The OFDM system is one of multicarrier modulation schemes and a system in which the multiple subcarriers, which form the multicarrier signal (multicarrier signal generated by the OFDM system is particularly referred to as an OFDM signal), are orthogonal to each other. The use of OFDM system enables to overlap the spectrum of the respective subcarriers, thereby allowing improvement in spectrum efficiency.
The transmission RF section 16 provides predetermined radio processing (D/A conversion, upconvert, and the like) to the multicarrier signal input from the IFFT section 15, and thereafter transmits the multicarrier signal to a radio receiving apparatus shown in FIG. 2 through the antenna 17.
FIG. 2 is a block diagram illustrating a configuration of a radio receiving apparatus according to Embodiment 1 of the present invention. The radio receiving apparatus illustrated in FIG. 2 includes an antenna 21, a reception RF section 22, an FFT section 23, a P/S section 24, a P/S section 25, a demodulating section 26 having a 16QAM section 261 and a 16QAM section 262, and a combining section 27, and receives a multicarrier signal sent from the radio transmitting apparatus shown in FIG. 1 to combine likelihoods of multiple same bits included in the multicarrier signal.
The reception RF section 22 provides predetermined radio processing (downconvert, A/D conversion and the like) to the multicarrier signal received through the antenna 21.
The FFT section 23 provides FFT (Fast Fourier Transform) processing to the multicarrier signal input from the reception RF section 22. This divides the multicarrier signal into multiple symbols for each carrier. One half of the multiple symbols after division is input to the P/S section 24 in parallel, and the other half is input to the P/S section 25 in parallel.
The S/P section 24 series converts a symbol sequence input in parallel from the FFT section 23, and inputs it to the 16QAM section 261. Moreover, the S/P section 25 series converts a symbol sequence input in parallel from the FFT section 23, and inputs it to the 16QAM section 262.
The 16QAM section 261 demodulates the symbol using a 16QAM demodulation scheme and thereafter calculates a likelihood for each bit. Moreover, the 16QAM section 262 demodulates the symbol using a 16QAM demodulation scheme and thereafter calculates a likelihood for each bit.
Since the same bit as the bit included in the bit sequence input from the 16QAM section 261 is included in the bit sequence input from the 16QAM section 262, the combining section 27 combines the likelihoods of the multiple same bits. The combination in this way allows improvement in the reception quality.
An explanation will next be given of the operations of the above-configured radio transmitting apparatus and radio receiving apparatus.
FIG. 3 is a view illustrating a mapping of each symbol in QPSK modulation. Moreover, FIG. 4 is a view illustrating a mapping of each symbol in 16QAM modulation. As illustrated in FIG. 3, since four mapping positions (namely, modulation level is 4) are provided in QPSK, the number of bits that can be included to one symbol to be transmitted is two. In contrast to this, as illustrated in FIG. 4, since 16 mapping positions (namely, modulation level is 16) are provided in 16QAM, the number of bits that can be included to one symbol to be transmitted is four. By changing the modulation scheme to 16QAM from QPSK in this way, the number of bits that can be included to one symbol to be transmitted can be doubled. Namely, the higher the modulation level is, the larger the number of bits that can be transmitted by one symbol is.
Additionally, in FIGS. 3 and 4, b1, b2, b3, and b4 are bit numbers showing positions where bits are arranged in the symbol, respectively. For example, in FIG. 4, b4 indicates the most significant bit and b1 indicates the least significant bit.
In the case where the modulation scheme is QPSK, a corresponding relationship between a subcarrier and a transmission bit is illustrated as in FIG. 5. In FIG. 5, a multicarrier signal includes 16 subcarriers of f1 to f16. Also, this shows a case in which a bit sequence of 32 bits of bits 1 to 32 is QPSK modulated and transmitted by 16 subcarriers of f1 to f16. Since the bit sequence of 32 bits is QPSK modulated, 16 symbols of S1 to S16 are generated. Symbols S1 to S16 are allocated to subcarriers f1 to f16, respectively. Furthermore, each symbol includes two bits.
Meanwhile, the radio transmitting apparatus illustrated in FIG. 1 uses 16QAM for the modulation scheme. As explained above, in 16QAM, the number of bits, which is twice as large as QPSK, can be transmitted by the same symbol. Namely, the change of QPSK to 16QAM makes it possible to transmit 64 bits by 16 symbols and 16 subcarriers. In other words, 32 bits, which were transmitted by 16 subcarriers in QPSK, can be transmitted by the half, that is, eight subcarriers in 16QAM. That is, the change of QPSK to 16QAM generates allowance in 8 subcarriers. Accordingly, the radio transmitting apparatus shown in FIG. 1 transmits the duplicated same bits 1 to 32 by 8 subcarriers having the generated allowance. This can be specifically explained as follows.
FIG. 6 is a view illustrating a corresponding relationship between a subcarrier and a transmission bit according to Embodiment 1 of the present invention. First of all, the radio transmitting apparatus shown in FIG. 1 duplicates the bit sequence of bits 1 to 32. Then, it is assumed that the bits 1 to 32 of the duplicating source are 16QAM modulated to be set as symbols S1 to S8 and that the duplicated bits 1 to 32 are 16QAM modulated to be set as symbols S9 to S16. Each of the multiple same bits is thereby included in the different symbol. For example, as illustrated in FIG. 6, the bits 1 to 4 are included in both symbols S1 and S9.
Here, in this embodiment, since the modulation scheme was changed from QPSK to 16QAM (the modulation level was changed from 4 to 16), the same bit was duplicated to create two same bits. However, the modulation scheme may be changed from QPSK to 64QAM or 256QAM. In the case of 64QAM, namely, when the modulation level is 64, the number of bits, which is three times as that of QPSK, can be transmitted by the same number of symbols and subcarriers as those of QPSK. Accordingly, in the case of 64QAM, the same bit is duplicated to create three same bits. Furthermore, in the case of 256QAM, namely, when the modulation level is 256, the number of bits, which is four times as that of QPSK, can be transmitted by the same number of symbols and subcarriers as those of QPSK. Accordingly, in the case of 256QAM, the same bit is duplicated to create four same bits. In addition, the modulation scheme is changed from BPSK to QPSK, making it possible to transmit the number of bits, which is two times as that of BPSK.
The symbol sequence of symbols S1 to S8 and the symbol sequence of symbols S9 to S16 are series-parallel converted individually, and thereafter subjected to IFFT processing. By IFFT processing, as illustrated in FIG. 6, the symbols S1 to S8 are allocated to the subcarriers f1 to f8. Moreover, the symbols S9 to S16 are allocated to the subcarriers f9 to f16 having allowance generated by changing the modulation scheme to 16QAM from QPSK. In other words, the bits 1 to 32 of the duplicating source are allocated to the subcarriers f1 to f8 and the duplicated bits 1 to 32 are allocated to the subcarriers f9 to f16. As a result, the same bits are allocated to the subcarriers each having a different frequency. For example, bit 1 is allocated to both subcarriers f1 and f9. Bit 1 is thereby transmitted by two frequencies of frequency 1 and frequency f9. The multicarrier signal including the subcarriers f1 to f16 is transmitted to the radio receiving apparatus as illustrated in FIG. 2.
As illustrated in FIG. 7, fading variation in a frequency axial direction is largely changed by an influence of a multipath. For this reason, a reception level varies for each subcarrier. Therefore, even if a reception level of bit 1 allocated to the subcarrier f1 is low, a reception level of bit 1 allocated to the subcarrier f9 is high in some cases.
The radio receiving apparatus of FIG. 2, which received the multicarrier signal, combines the likelihoods of the same bits allocated to the different subcarriers. For example, the radio receiving apparatus combines the likelihood of bit 1 allocated to the subcarrier f1 and that of bit 1 allocated to the subcarrier f9. This enables to obtain frequency diversity gain, allowing improvement in the reception quality of bits 1 to 32 included in the bit sequence.
In addition, it can be considered that an error rate characteristic deteriorates as shown in FIG. 8 if no processing is performed after the modulation scheme is changed to 16QAm from QPSK. In FIG. 8, 31 denotes an error rate characteristic of QPSK, and 32 denotes an error rate characteristic of 16QAM. However, according to this embodiment, it can be considered that since the likelihoods of the multiple same bits each having a different frequency, which are included in the multicarrier signal, are combined with each other, frequency diversity gain is obtained, with the result that the error rate characteristic is more improved than QPSK as shown by 33.
As mentioned above, according to this embodiment, the multicarrier signal, which includes the multiple same bits each having a different frequency, is transmitted and the likelihoods of the multiple same bits each having a different frequency, which are included in one multicarrier signal, are combined with each other. For this reason, diversity gain in the frequency axial direction can be obtained by one transmission. Namely, it is possible to improve the reception quality without performing transmission and retransmission by a plurality of antennas. Moreover, diversity gain can be obtained without changing a transmission rate, enabling to improve the reception quality. Furthermore, since the higher the modulation level is, the larger the number of same bits included in the multicarrier signal, it is possible to further improve diversity gain in the frequency axial direction by increasing the modulation level.
Embodiment 2
The fading variation normally has a periodicity in the frequency axial direction as illustrated in FIG. 9. For this reason, if the symbols having the same bits are periodically arranged, the reception levels of all same bits largely drop, so that diversity gain cannot be obtained in some cases.
Accordingly, this embodiment prevents the symbols having the same bits from being periodically arranged on the frequency axis. For example, in FIG. 6, a distance between symbols S1 and S9 on the frequency axis is made different from a distance between symbols S2 and S10 on the frequency axis. This is achieved by the following configuration.
FIG. 10 is a block diagram illustrating a configuration of a radio transmitting apparatus according to Embodiment 2 of the present invention. However, the same reference numerals as those of the components (FIG. 1) of Embodiment 1 are added to the same components of Embodiment 1, and the explanation will be omitted. An interleaving section 18 rearranges the order of the symbol sequence output from the modulating section 12. Namely, the interleaving section 18 interleaves the symbol sequence according to a predetermined interleaving pattern.
Moreover, FIG. 11 is a block diagram illustrating a configuration of a radio receiving apparatus according to Embodiment 2 of the present invention. However, the same reference numerals as those of the components (FIG. 2) of Embodiment 1 are added to the same components of Embodiment 1, and the explanation will be omitted. A deinterleaving section 28 rearranges the order of the symbol sequence output from the P/S section 24 and the P/S section 25 in reverse to the interleaving made by the radio transmitting apparatus to set a symbol sequence which is in a state that interleaving is not yet made. In other words, the symbol sequence is deinterleaved according to the interleaving made by the radio transmitting apparatus.
An explanation will next be given of a symbol interleaving method. According to this embodiment, any one of the following three methods shown in FIGS. 12 to 14 is performed as a symbol interleaving.
In the interleaving method illustrated in FIG. 12, the order of the symbol sequence having the bits of the duplicating source is unchanged, and the order of the symbol sequence having the duplicated bits is reversed to the order of the symbol sequence having the bits of the duplicating source. Accordingly, symbol S9, which was allocated to the subcarrier f9 in FIG. 6, is allocated to the subcarrier f16 in FIG. 12. Moreover, symbol S16, which was allocated to the subcarrier f16 in FIG. 6, is allocated to the subcarrier f9 in FIG. 12. This enables to prevent the distance between the symbols having the same bits from being conformed to the periodicity of fading variation. This makes it possible to improve frequency diversity effect as compared with Embodiment 1.
Furthermore, in the interleaving method illustrated in FIG. 13, the order of the symbol sequence having the bits of the duplicating source is unchanged, and the order of the symbol sequence having the duplicated bits is rearranged regardless of the order of the symbol sequence having the bits of the duplicating source. For example, as illustrated in FIG. 13, only symbols S9 to S16 are rearranged. This enables to prevent the distance between the symbols having the same bits from being conformed to the periodicity of fading variation. Also, as compared with the interleaving method shown in FIG. 12, fading variation that the same bits receive becomes large, enhancing more frequency diversity effect.
Furthermore, in the interleaving method shown in FIG. 14, the symbol sequence having the bits of the duplicating source and the symbol sequence having the duplicated bits are combined and rearranged. For example, as illustrated in FIG. 14, all symbols S1 to S16 are rearranged. Similar to FIG. 12, this enables to prevent the distance between the symbols having the same bits from being conformed to the periodicity of fading variation. Also, as compared with the interleaving method shown in FIG. 13, fading variation that the same bits receive becomes much large, enhancing much more frequency diversity effect.
In this embodiment, according to this configuration, when the fading variation in the frequency axial direction has a periodicity, magnitude in the fading variation that each of the multiple same bits receives at a transmission path can be made different, so that frequency diversity gain in the frequency axial direction can be more improved.
Embodiment 3
This embodiment prevents the multiple same bits from being periodically arranged on the frequency axis. This is achieved by the following configuration.
FIG. 15 is a block diagram illustrating a configuration of a radio transmitting apparatus according to Embodiment 3 of the present invention. However, the same reference numerals as those of the components (FIG. 1) of Embodiment 1 are added to the same components of Embodiment 1, and the explanation will be omitted. An interleaving section 19 rearranges the order of the symbol sequence output from the duplicating section 11. Namely, the interleaving section 19 interleaves the bit sequence according to a predetermined interleaving pattern.
The 16QAM section 121 modulates the bit sequence of higher-order 32 bits of 64 bits by use of 16QAM modulation scheme to form a symbol. Further, the 16QAM section 122 modulates the bit sequence of lower-order 32 bits of 64 bits by use of 16QAM modulation scheme to form a symbol.
Furthermore, FIG. 16 is a block diagram illustrating a configuration of a radio receiving apparatus according to Embodiment 3 of the present invention. However, the same reference numerals as those of the components (FIG. 2) of Embodiment 1 are added to the same components of Embodiment 1, and the explanation will be omitted. A deinterleaving section 29 rearranges the order of the bit sequence output from the demodulating section 26 in reverse to the interleaving made by the radio transmitting apparatus to set a symbol sequence which is in a state that interleaving is not yet made. In other words, the bit sequence is deinterleaved according to the interleaving made by the radio transmitting apparatus.
An explanation will next be given of a bit interleaving method. According to this embodiment, either of two methods shown in FIGS. 17 and 18 is performed as a bit interleaving.
In the interleaving method illustrated in FIG. 17, the order of the bit sequence of the duplicating source is unchanged, and the order of the duplicated bit sequence duplicated is rearranged regardless of the order of the bit sequence of the duplicating source. For example, as illustrated in FIG. 17, only the duplicated bits 1 to 32 are rearranged. This enables to prevent the distance between the same bits on the frequency axis from being conformed to the periodicity of fading variation. Also, fading variation that the same bits receive becomes large, enhancing more frequency diversity effect.
Furthermore, in the interleaving method shown in FIG. 18, the bit sequence of the duplicating source and the duplicated bit sequence are combined and rearranged. For example, as illustrated in FIG. 18, all of the bits 1 to 32 of the duplicating source and the duplicated bits 1 to 31 are rearranged. Similar to FIG. 17, this enables to prevent the distance between the symbols having the same bits from being conformed to the periodicity of fading variation. Also, as compared with the interleaving method shown in FIG. 17, fading variation that the same bits receive becomes much large, enhancing much more frequency diversity effect.
According to this embodiment, when the fading variation has a periodicity in the frequency axial direction, the fading variation that each of the multiple same bits receives at a transmission path increases, thereby more improving frequency diversity gain in the frequency axial direction.
Embodiment 4
In 16QAM, among four bits included in one symbol, the likelihood of the higher-order two bits is higher than that of the lower-order two bits from the relationship among the mapping positions of 16 points of the symbols. This embodiment uses this and performs modulation such that the positions where the multiple same bits are arranged are made different from one another in the symbol having the bits of the duplicating source and the symbol having the duplicated bits. Namely, in the symbol having the bits of the duplicating source and the symbol having the duplicated bits, modulation is performed such that their mappings are made different from one another. This is achieved by the following configuration.
FIG. 19 is a block diagram illustrating a configuration of a radio transmitting apparatus according to Embodiment 4 of the present invention. However, the same reference numerals as those of the components (FIG. 1) of Embodiment 1 are added to the same components of Embodiment 1, and the explanation will be omitted. According to a mapping pattern given by mapping information 1 shown in FIG. 20, the 16QAM section 123 modulates the bit sequence of the duplicating source by use of 16QAM modulation scheme to form a symbol. Also, according to a mapping pattern given by mapping information 2 shown in FIG. 21, the 16QAM section 124 modulates the duplicated bit sequence by use of 16QAM modulation scheme to form a symbol.
For example, attention is paid to a mapping point 41 in FIGS. 20 and 21. In FIG. 20, higher-order two bits are “00” and lower-order two bits are “11.” In FIG. 21, higher-order two bits are “11” and lower-order two bits are “00.” Accordingly, the same bits as those arranged at the higher-order two bits of the symbol by the 16QAM section 123 are arranged at the lower-order two bits of the symbol by the 16QAM 124. Also, the same bits as those arranged at the lower-order two bits of the symbol by the 16QAM section 123 are arranged at the higher-order two bits of the symbol by the 16QAM section 124.
Herein, a corresponding relationship between a subcarrier and a transmission bit is illustrated by FIG. 22. For example, attention is paid to symbols S1 and S9 having the same bits. Bits 3 and 4 arranged at higher-order two bits of symbol S1 are arranged at the lower-order two bits of the symbol S9. Also, bits 1 and 2 arranged at lower-order two bits of symbol S1 are arranged at the higher-order two bits of the symbol S9. Accordingly, in symbol S1, the likelihoods of bits 3 and 4 are higher than those of bits 1 and 2. Conversely, in symbol S9, the likelihoods of bits 1 and 2 are higher than those of bits 3 and 4.
An explanation will next be given of the radio receiving apparatus. FIG. 23 is a block diagram illustrating a configuration of a radio receiving apparatus according to Embodiment 4 of the present invention. However, the same reference numerals as those of the components (FIG. 2) of Embodiment 1 are added to the same components of Embodiment 1, and the explanation will be omitted. According to the mapping pattern given by mapping information 1 shown in FIG. 20, the 16QAM section 263 demodulates the symbol by use of 16QAM modulation scheme to form a bit sequence. Also, according to the mapping pattern given by mapping information 2 shown in FIG. 21, the 16QAM section 264 demodulates the symbol by use of 16QAM modulation scheme to form a bit sequence.
The combining section 27 combines the likelihoods of the multiple same bits similar to Embodiment 1. As mentioned above, attention is paid to the mapping point 41. The same bits as “00” with high likelihoods arranged at the higher-order two bits (b4, b3) in FIG. 20 are arranged at lower-order two bits (b2, b1) and the likelihoods are reduced in FIG. 21. Also, the same bits as “11” with low likelihoods arranged at the lower-order two bits (b2, b1) in FIG. 20 are arranged at higher-order two bits (b4, b3) and the likelihoods are increased in FIG. 21. Accordingly, the combining 27 combines the likelihoods of the multiple same bits as illustrated in FIG. 24. Namely, the likelihood of “0” arranged at b4 is combined with that of “0” arranged at b2. The likelihood of “0” arranged at b3 is combined with that of “0” arranged at b1. The likelihood of “1” arranged at b2 is combined with that of “1” arranged at b4. The likelihood of “1” arranged at b1 is combined with that of “1” arranged at b3. This increases the respective bit likelihoods and equalizes them as compared with the case in which combining is not yet made.
As mentioned above, according to the present embodiment, the likelihoods of the multiple same bits each having a different likelihood are combined with each other to enable to increase the likelihoods of the multiple same bits and equalize them, thereby making it possible to more improve the reception quality.
In addition, the radio transmitting apparatus and radio receiving apparatus of the present invention are suitable for use in a radio communication terminal apparatus and a radio communication base station apparatus employed in, for example, a mobile communication system and the like. The radio transmitting apparatus and radio receiving apparatus of the present invention are installed on the radio communication terminal apparatus and the radio communication base station apparatus, thereby enabling to provide the radio transmitting apparatus and radio receiving apparatus having the same functions and effect as mentioned above.
Moreover, the present invention can be applied to a multicarrier CDMA (MC-CDMA) that performs spreading in a frequency axial direction. In the case of this application, since likelihood variation becomes large for each spread code by interference variation between spread codes that is caused by a difference in fading variation for each subcarrier, it can be expected that diversity effect will be more increased.
Furthermore, the present invention can be applied to a multicarrier CDMA (MC/DS-CDMA) that performs spreading in a time axial direction. In the case of this application, regarding a problem in which a signal, which is transmitted by a specific subcarrier, deteriorates extremely by a difference in fading variation for each subcarrier, performance can be improved by diversity effect.
As explained above, according to the present invention, it is possible to improve reception quality without performing transmission and retransmission using a plurality of antennas.
This application is based on the Japanese Patent Application No. 2002-052831 filed on Feb. 28, 2002, entire content of which is expressly incorporated by reference herein.

## Claims

1. A radio transmitting apparatus that transmits a multicarrier signal including a plurality of subcarriers, said radio transmitting apparatus comprising:
a duplicating section that duplicates a bit sequence to generate a plurality of same bits;
a modulating section that performs modulation to include each of the plurality of same bits to a different symbol;
a generating section that allocates each of the symbols modulated by said modulating section to each of the subcarriers each having a different frequency to generate the multicarrier signal; and
a transmitting section that transmits the multicarrier signal generated by said generating section, wherein:
said duplicating section obtains N/M of the plurality of same bits, where M is the number of bits for one symbol in a reference modulation scheme, N is the number of bits for one symbol in a modulation scheme used in said modulating section, and N/M is an integer greater than one.

2. The radio transmitting apparatus according to claim 1, further comprising a symbol interleaving section that rearranges the order of a symbol sequence output from said modulating section.

3. The radio transmitting apparatus according to claim 1, further comprising a bit interleaving section that rearranges the order of a bit sequence output from said duplicating section.

4. The radio transmitting apparatus according to claim 1, wherein when each of the plurality of same bits is included in the different symbol, said modulating section makes positions where the plurality of same bits are arranged different from each other in the different symbol.

5. A radio communication terminal apparatus having the radio transmitting apparatus according to claim 1.

6. A radio communication base station apparatus having the radio transmitting apparatus according to claim 1.

7. A radio receiving apparatus comprising:
a receiving section that receives a multicarrier signal including a plurality of subcarriers where each of a plurality of same bits is allocated to each of the subcarriers each having a different frequency; and
a combining section that combines likelihoods of the plurality of same bits, wherein:
the number of the plurality of same bits is N/M, where M is the number of bits for one symbol in a reference modulation scheme, N is the number of bits for one symbol in a modulation scheme used in a transmission side of the multicarrier signal, and N/M is an integer greater than one.

8. A radio communication terminal apparatus having the radio receiving apparatus according to claim 7.

9. A radio communication base station apparatus having the radio receiving apparatus according to claim 7.

10. A radio transmitting method for transmitting a multicarrier signal including a plurality of subcarriers, said radio transmitting method comprising the steps of:
(a) duplicating a bit sequence to generate a plurality of same bits;
(b) performing modulation to include each of the plurality of same bits to a different symbol;
(c) allocating each of the symbols modulated in the step (b) to each of the subcarriers each having a different frequency to generate the multicarrier signal; and
(d) transmitting the multicarrier signal generated in the step (c), wherein:
in the step (a), obtaining N/M of the plurality of same bits, where M is the number of bits for one symbol in a reference modulation scheme, and N is the number of bits for one symbol in a modulation scheme used in the step (b), and N/M is an integer greater than one.