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In the case of transmitting a signal of at least three bits in one symbol, when receiving a retransmission request signal from a radio station of a communication partner, a transmission apparatus 10A retransmits only the bits (lower bits) that are susceptible to error, without retransmitting the bit

In the case of transmitting a signal of at least three bits in one symbol, when receiving a retransmission request signal from a radio station of a communication partner, a transmission apparatus 10A retransmits only the bits (lower bits) that are susceptible to error, without retransmitting the bits (higher bits) that are not readily susceptible to error and that are obtained by processing in a modulation section 11. A reception apparatus 10B of the communication partner performs error correction processing using the bits (higher bits) and that are stored in memories 16 and 17 and that are not readily susceptible to error, and the bits that are obtained by retransmission and that are susceptible to error (lower bits).

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The invention claimed is: 1. A transmission/reception apparatus comprising: a transmission section that transmits data to a communication partner by using a modulation scheme, the data comprising P bits (P≧3) and the modulation scheme assigning the P bits to one symbol; and a reception secti

The invention claimed is: 1. A transmission/reception apparatus comprising: a transmission section that transmits data to a communication partner by using a modulation scheme, the data comprising P bits (P≧3) and the modulation scheme assigning the P bits to one symbol; and a reception section that receives a re-transmission request signal from the communication partner, the re-transmission request signal showing a request for re-transmitting the data from the transmission/reception apparatus to the communication partner, wherein said transmission section re-transmits, in response to receiving the re-transmission request signal for requesting the re-transmitting of the data, only susceptible bits among the P bits of the data to the communication partner, the susceptible bits comprising R bits (R<P) and being susceptible to error due to assigning P bits of the data to the one symbol in the modulation scheme. 2. The transmission/reception apparatus according to claim 1, wherein said transmission section changes the number of re-transmitting R bits according to channel quality. 3. The transmission/reception apparatus according to claim 1, further comprising: a first modulation section that modulates data comprising P1 bits into one symbol; a second modulation section that modulates data comprising P2 bits (P2>P1) into one symbol; and a modulation scheme selection section that selects one of the modulation sections, wherein said modulation scheme selection section selects said first modulation section when the re-transmission request signal is received by said reception section, and selects said second modulation section when no re-transmission request signal is received by said reception section. 4. The transmission/reception apparatus according to claim 1, wherein said transmission section comprises a 16-level QAM modulation section that, when the re-transmission request signal is received, re-transmits only two bits that are more susceptible to error anion four bits assigned to one symbol previously transmitted. 5. The transmission/reception apparatus according to claim 1, wherein said transmission section comprises an M-ary modulation section that when the re-transmission request signal is received, re-transmits only lower two bits that are more susceptible to error among at least six bits assigned to one symbol previously transmitted. 6. The transmission/reception apparatus according to claim 1, further comprising an OFDM modulation section that superimposes a transmission signal on a plurality of subcarriers orthogonal to each other, wherein, when a re-transmission request is received, the OFDM modulation section superimposes the re-transmission signal on a different subcarrier from a subcarrier on which a transmission signal is superimposed when the re-transmission request is not received. 7. A transmission/reception apparatus comprising: a reception/demodulation section that receives a transmission signal where data comprising P bits, which is at least three bits, is modulated into one symbol and transmitted, and demodulates the received signal into the data comprising P bits per one symbol; a memory section that stores higher Q bits (Q<P) of the demodulated data comprising P bits forming one symbol, that are less susceptible to error; a re-transmission request section that transmits a re-transmission request signal to a communication partner when a signal error occurs in the signal demodulated by said reception/demodulation section; and an error correction section that performs error correction processing using data comprising lower bits excluding the higher Q bits in one symbol, sent from the communication partner in response to receiving the re-transmission request signal at the communication partner, and data comprising the higher Q bits in one symbol, stored in said memory section. 8. The transmission/reception apparatus according to claim 7, wherein said reception/demodulation section receives a signal where data comprising at least six bits is transmitted in one symbol; and wherein said memory section stores higher four bits among the data demodulated by said reception/demodulation section when said re-transmission request section transmits a first re-transmission signal, and stores higher two bits among the data demodulated by said reception/demodulation section when said re-transmission request section transmits a next re-transmission signal for the same data. 9. The transmission/reception apparatus according to claim 7, wherein said reception/demodulation section receives a signal where data comprising at least six bits is transmitted in one symbol; and wherein said memory section stores four bits of the data demodulated by said reception/demodulation section that are less susceptible to error. 10. The transmission/reception apparatus according to claim 7, further comprising a channel quality detection section that detects channel quality between the communication partner and the transmission/reception apparatus, wherein said re-transmission request section changes the number of bits to request re-transmission from the communication partner according to the detected channel quality. 11. The transmission/reception apparatus according to claim 10, wherein said re-transmission request section reduces the number of bits to request re-transmission as the channel quality detected by said channel quality detection section improves; and wherein: said memory section increases the number of higher bits to be stored as the channel quality detected by said channel quality detection section improves. 12. The transmission/reception apparatus according to claim 11, wherein said channel quality detection section detects a signal level of the received signal obtained by said reception/demodulation section as the channel quality; wherein, based on the detected signal level, said re-transmission request section transmits a re-transmission request signal instructing to make that the number of lower bits to be re-transmitted smaller as the signal level increases; and wherein, based on the detected signal level, said memory section increases the number of the higher bits to be stored as the signal level increases. 13. The transmission/reception apparatus according to claim 7, wherein said reception/demodulation section further comprises a delay dispersion detection section that receives an OFDM signal where transmission data is superimposed on a plurality of subcarriers orthogonal to each other, and detects an amount of delay dispersion of the received signal obtained by said reception/demodulation section; wherein, based on the amount of delay dispersion detected by said delay dispersion detection section, said re-transmission request section transmits a re-transmission request signal instructing to make the number of lower bits to be re-transmitted smaller as the amount of delay dispersion decreases; and wherein, based on the amount of delay dispersion detected by said delay dispersion detection section, said memory section increases the number of higher bits to be stored as the amount of delay dispersion decreases. 14. The transmission/reception apparatus according to claim 7, wherein said reception/demodulation section further comprises: a signal level detection section that detects a signal level of the received signal obtained by said reception/demodulation section in addition to receiving an OFDM signal where transmission data is superimposed on a plurality of subcarriers orthogonal to each other; a delay dispersion detection section that detects an amount of delay dispersion of the received signal obtained by said reception/demodulation section; a threshold level selection section that selects a higher threshold level as the amount of delay dispersion detected by said delay dispersion detection section increases, as a threshold for the signal level of the received signal; and a comparison section that compares the signal level of the received signal with the threshold level selected by said threshold level selection section; and wherein, when a comparison result indicating that the signal level is higher than the threshold level is obtained by said comparison section, said re-transmission request section transmits a re-transmission request signal instructing to make the number of lower bits to be re-transmitted smaller, and said memory section increases the number of higher bits to store. 15. The transmission/reception apparatus according to claim 13, wherein said delay dispersion detection section uses a level normalized by the signal level of the received signal as the amount of delay dispersion. 16. A transmission/reception method comprising the steps of: receiving a transmission signal where data comprising P bits, which is at least three bits, is modulated into one symbol and transmitted; demodulating the received signal into the data comprising P bits per one symbol; storing higher Q bits of the demodulated data comprising P bits per one symbol, that are less susceptible to error; transmitting a re-transmission request signal to a communication partner when a signal error occurs in the demodulated signal; and performing error correction processing using data comprising lower bits excluding the higher Q bits in one symbol, sent from the communication partner in response to receiving the re-transmission request signal at the communication partner, and data comprising the stored higher Q bits in one symbol. 17. A transmission/reception method comprising the steps of: transmitting data to a communication partner by using a modulation scheme, the data comprising P bits (P≧3) and the modulation scheme assigning the P bits to one symbol; and receiving a re-transmission request signal from the communication partner, the re-transmission request signal showing a request for re-transmitting the data from the transmission/reception apparatus to the communication partner; wherein in said step of transmitting, in response to receiving the re-transmission request signal for requesting the re-transmitting of the data, only susceptible bits among the P bits of the data are re-transmitted to the communication partner, the susceptible bits comprising R bits (R<P) and being susceptible to error due to assigning P bits of the data to the one symbol in the modulation scheme.