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An encoder and a decoder each having an error correcting operation, and a data transmission apparatus using them for data transmission in a multilevel modulation system. In transmission data is converted into parallel data. One bit thereof is inputted to a convolutional encoder to output two bits. T

An encoder and a decoder each having an error correcting operation, and a data transmission apparatus using them for data transmission in a multilevel modulation system. In transmission data is converted into parallel data. One bit thereof is inputted to a convolutional encoder to output two bits. Two bit data and another signal of the parallel data not inputted to the convolutional encoder are respectively separated into real part and imaginary part to independently decide signal points for the parallel data. In reception an area is similarly decided independently for real and imaginary parts and metric is assigned for the data. Real and imaginary parts are combined with each other for Viterbi decoding. Result thereof is fed to a convolutional encoder similar in constitution to that on transmission side. Using convolutional encoding output and decided area, transmission data is decoded.

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1. An encoder with error correction for use in a transmitting apparatus which sends data in a 2 nQAM system (n is an integer equal to or more than four), comprising: a converting section for converting said data into (n−1)-bit parallel data; a convolutional encoder for receiving one bit of

1. An encoder with error correction for use in a transmitting apparatus which sends data in a 2 nQAM system (n is an integer equal to or more than four), comprising: a converting section for converting said data into (n−1)-bit parallel data; a convolutional encoder for receiving one bit of the (n−1)-bit parallel data; and a signal point generator for receiving 2-bit data outputted from said convolutional encoder and data including remaining bits of the (n−1)-bit parallel data, wherein the 2-bit data from said convolutional encoder and the data of the remaining bits of the (n−1)bit—parallel data are separated, respectively, into an in-phase component and a quadrature component, each of which is inputted to said signal point generator; said signal point generator generates multilevel signals according to the 2 nQAM system which includes said multilevel signals constituted as below, so as to be able to simply decode in a decoder:in a signal point plane of an in-phase amplitude component (I)—quadrature amplitude component (Q) coordinate system, an identical bit layout is assigned to in-phase components at signal points having an identical in-phase amplitude component and an identical bit layout is assigned to quadrature components at signal points having an identical quadrature amplitude component;for in-phase components at signal points adjacent to each other in a direction of an in-phase amplitude component axis mutually different bit value is assigned to the lowest bit of an in-phase component output from said convolutional encoder, regardless of each quadrant of I-Q coordinate system;so that said signal points are independently assigned to each other in said in-phase components and said quadrature components in the direction of said in-phase and quadrature amplitude components axis, respectively, and each of said signal points according to said signals output from said convolutional encoder is assigned in an identical bit layout in each quadrant of I-Q coordinate system.2. An encoder with error correction for use in a transmitting apparatus which sends data in a 2 nQAM system (n is an integer equal to or more than four), comprising: a converting section for converting said data into (n−1)-bit parallel data; a convolutional encoder for receiving one bit of the (n−1)-bit parallel data; and a signal point generator for receiving 2-bit data outputted from said convolutional encoder and data including remaining bits of the (n−1-bit parallel data, wherein the 2-bit data from said convolutional encoder and the data of the remaining bits of the (n−1)bit parallel data are separated, respectively, into an in-phase component and a quadrature component, each of which is inputted to said signal point generator; and said signal point generator generates multilevel signals according to the 2 nQAM system which includes said multilevel signals constituted as below, so as to be able to simply decode in a decoder:in a signal point plane of an in-phase amplitude component (I)—quadrature amplitude component (Q) coordinate system, said plane is divided into a first area and second areas;in said first area, an identical bit layout is assigned to in-phase components at signal points having an identical in-phase amplitude component and an identical bit layout is assigned to quadrature components at signal points having an identical quadrature amplitude component;in the first and second areas, mutually different bit values are assigned to the lowest bit of an in-phase component output from said convolutional encoder for signal points adjacent to each other in a direction of an in-phase amplitude component axis, regardless of each quadrant of I-Q coordinate system, and mutually different bit values are assigned to the lowest bit of a quadrature component output from said convolutional encoder at signal points adjacent to each other in a direction of a quadratur e amplitude component axis, regardless of each quadrant of I-Q coordinate system, andbit arrays not assigned to the first area are assigned to signal points in the second areas; so that said signal points are independently assigned to each other in said in-phase components and said quadrature components in the direction of said in-phase and quadrature amplitude components axis, respectively, and each of said signal points according to said signals output from said convolutional encoder is assigned in an identical bit layout in each quadrant of I-Q coordinate system, in the first and second areas. 3. An encoder with error correction according to claim 2, wherein in the second area, bit layouts not assigned to the first area are assigned such that: an identical bit layout, as available as possible from said bit layouts not assigned, is assigned to in-phase components at signal points having an identical in-phase amplitude component and/or; an identical bit layout, as available as possible from said bit layouts not assigned, is assigned to quadrature components at signal points having an identical quadrature amplitude component. 4. An encoder with error correction for use in a transmitting apparatus which sends data in a 2 nQAM system (n is an integer equal to or more than four), comprising: a converting section for converting said data into (n−1)-bit parallel data; a convolutional encoder for receiving one bit of the (n−1)-bit parallel data; and a signal point generator for receiving 2-bit data outputted from said convolutional encoder and data including remaining bits of the (n−1)-bit parallel data, wherein: the2-bit data from said convolutional encoder and the data of the remaining bits of the (n−1)bit—parallel data are separated, respectively, into an in-phase component and a quadrature component, each of which is inputted to said signal point generator;said signal point generator generates multilevel signals according to the 2nQAM system which includes said multilevel signals constituted as below, so as to be able to simply decode in a decoder:in a signal point plane of an in-phase amplitude (I) component - quadrature amplitude component (Q) coordinate system, said plane is divided into a first area and a plurality of second areas;in the first area, an identical bit layout is assigned to in-phase components at signal points having an identical in-phase amplitude component and an identical bit layout is assigned to quadrature components at signal points having an identical quadrature amplitude component;in the second areas, bit layouts not assigned to the first area are assigned such that an identical bit layout, as available as possible from said bit layouts not assigned, is assigned to in-phase components at signal points having an identical in-phase amplitude component;in the first and second areas, mutually different bit values are assigned to the lowest bit of an in-phase component output from said convolutional encoder at signal points adjacent to each other in a direction of an in-phase component axis, regardless of each quadrant of I-Q coordinate system, and mutually different bit values are assigned to the lowest bit of a quadrature component output from said convolutional encoder at signal points adjacent to each other in a direction of a quadrature amplitude component axis, regardless of each quadrant of I-Q coordinate system; andfor quadrature components at signal points in the second areas, bits of bit arrays not assigned yet are assigned to bits other than bits corresponding to the in-phase component output from said convolutional encoder; so that said signal points are independently assigned to each other in said in-phase components and said quadrature components in the direction of said in-phase and quadrature amplitude components axis, respectively, and each of said signal points according to said signals output from said convolutional encoder is assigned in an id entical bit layout in each quadrant of I-Q coordinate system, in the first and second areas. 5. An encoder with error correction for use with 2 nQAM signals (n is an integer equal to or more than four), an in-phase component signal and a quadrature component signal of said 2nQAM signals having mutually different bit values in a signal point plane of an in-phase amplitude component (I)—quadrature amplitude component (Q) coordinate system, regardless of each quadrant of said I-Q coordinate system, comprising: an area deciding section for receiving an in-phase component (I) signal and an quadrature component (Q) signal of the QAM signals, wherein said area deciding section decides, to which quadrant of a signal point plane of an in-phase amplitude component (I)—quadrature amplitude component (Q) coordinate system, said in-phase component (I) signal and said quadrant component (Q) signal belongs; first and second metric assigning sections for producing, based on the result of said area deciding section, metric for the in-phase component (I) and quadrature component (Q) signals, respectively; a Viterbi decoder for receiving the metrics for the in-phase component (I) and quadrature component (Q) signals; a convolutional encoder for receiving a data signal outputted from said Viterbi decoder; first and second decoders for being applied each of the in-phase component (I) and quadrature component (Q) signals from said area deciding section and said convolutional encoder, and a parallel/serial converter for receiving an output from said Viterbi decoder and outputs from said first and second decoders. 6. An decoder with error correction according to claim 5, wherein n is an even number equal to or more than four; said first decoder receives a data signal for said in-phase component signal from said convolutional encoder and the result from said area deciding section; said second decoder receives a data signal for said quadrature component signal from said convolutional encoder and the result from said area deciding section; and an output from said first decoder for the in-phase component signal, an output from said second decoder for the quadrature component signal, and the output from said Viterbi decoder are inputted to said parallel/serial converter. 7. A decoder with error correction according to claim 5, wherein n is an odd number equal to or more than five; said first decoder receives a data signal for said quadrature component signal from said convolutional encoder and the results for said in-phase component signal and for said quadrature component signal from said area deciding section; said second decoder receives a data signal for the quadrature component signal and a data signal for said in-phase component signal from said convolutional encoder, and the results of area decision for a quadrature component signal and for said in-phase component signal from said area deciding section, and an output from said first decoder for an in-phase component signal, an output from said second decoder for a quadrature component signal, and the output from said Viterbi decoder are inputted to said parallel/serial converter. 8. A data transmission apparatus for sending transmission data in a 2 nQAM system (n is an even number equal to or more than four), comprising: a transmitter section; and a receiver section, said transmitter section comprising: an encoder with error correction for receiving said data as an input signal, for converting said data into an in-phase component signal and a quadrature component signal in a parallel signal form, the in-phase component signal and the quadrature component signal being orthogonal to each other, and for outputting the signals therefrom; anda modulator section for receiving the in-phase and quadrature component signals from said encoder with error correction, for generating an analog modulated wave signal using the in-phase and quadrature component signals, and for outputting the analog modulated wave signal therefrom; said receiver section comprising: a demodulator section for receiving the analog modulated wave signal from said transmitter section and for demodulating the analog modulated wave signal to generate an in-phase component signal and a quadrature component signal; anda decoder with error correction for receiving the in-phase component signal and the quadrature component signal from said demodulator section and for decoding the in-phase and quadrature component signals, wherein said encoder with error correction comprising: a converter section for converting said data into (n−1)-bit parallel data;a convolutional encoder for receiving one bit of the (n−1)-bit parallel data; anda signal point generator for receiving 2-bit data outputted from said convolutional encoder and data including remaining bits of the (n−1)-bit parallel data, wherein each of the 2-bit data from said convolutional encoder and said data including remaining bits of the (n−1)-bit parallel data is separated into an in-phase component and a quadrature component to be fed to said signal point generator, and wherein said signal point generator thereby generates a multilevel signal according to the 2 nQAM system which includes multilevel signals formed as below:in a signal point plane of an in-phase amplitude component (I)—quadrature amplitude component (Q) coordinate system, an identical bit layout is assigned to in-phase components at signal points having an identical in-phase amplitude component and an identical bit layout is assigned to quadrature components at signal points having an identical quadrature amplitude component;for in-phase components at signal points adjacent to each other in a direction of an in-phase amplitude component axis, mutually different bit value is assigned to the lowest bit of an in-phase component output from said convolutional encoder, regardless of each quadrant if I-Q coordinate system,so that said signal points are independently assigned to each other in said in-phase components and said quadrature components in the direction of said in-phase and quadrature amplitude components axis, respectively, and each of said signal points according to said signals output from said convolutional encoder is assigned in an identical bit layout in each quadrant of I-Q coordinate system.9. A data transmission apparatus for sending transmission data in a 2 nQAM system (n is an odd number equal to or more than five), comprising: a transmitter section; and a receiver section, said transmitter section comprising: an encoder with error correction for receiving said data as an input signal, for converting said data into an in-phase component signal and a quadrature component signal in a parallel signal form, the in-phase component signal and the quadrature component signal being orthogonal to each other, and for outputting the signals therefrom; anda modulator section for receiving the in-phase and quadrature component signals from said encoder with error correction, for generating an analog modulated wave signal using the in-phase and quadrature component signals, and for outputting the analog modulated wave signal therefrom; said receiver section comprising: a demodulator section for receiving the analog modulated wave signal from said transmitter section and for demodulating the analog modulated wave signal to generate an in-phase component signal and a quadrature component signal; anda decoder with error correction for receiving the in-phase component signal and the quadrature component signal from said demodulator section and for decoding the in-phase and quadrature component signals, wherein said encoder with error correction comprising: a converting section for converting said data into (n−1)-bit parallel data;a convolutional encoder for receiving one bit of the (n−1)-bit parallel data; anda signal point generator for receiving 2-bit data outputted from said convolutional encoder and data including remaining bits of the (n−1)-bit parallel data, wherein each of the 2-bit data from said convolutional encoder and said data including remaining bits of the (n−1)-bit parallel data is separated into an in-phase component and a quadrature component to be fed to said signal point generator, and wherein said signal point generator thereby generates a multilevel signal according to the 2 nQAM system which includes multilevel signals formed as below:in a signal point plane of an in-phase amplitude component (I)—quadrature amplitude component (Q) coordinate system, said plane is divided into a first area and a plurality of second areas;in the first area, an identical bit layout is assigned to in-phase components at signal points having an identical in-phase amplitude component and an identical bit layout is assigned to quadrature components at signal points having an identical quadrature amplitude component;in the first and second areas, mutually different bit values are assigned to the lowest bit of an in-phase component output from said convolutional encoder for signal points adjacent to each other in a direction of an in-phase amplitude component axis, regardless of each quadrant of I-Q coordinate system, and mutually different bit values are assigned to bits corresponding to a quadrature component output from said convolutional encoder at signal points adjacent to each other in a direction of a quadrature amplitude component axis, regardless of each quadrant of I-Q coordinate system; andbit arrays not assigned to the first area are assigned to signal points in the second areas; andmutually different bit layouts are assigned to respective signal points in the first and second areas.10. A data transmission apparatus according to claim 9, wherein: in the second areas, bit layouts not assigned to the first area are assigned such that: an identical bit layout, as available as possible from said bit layouts not assigned, is assigned to in-phase components at signal points having an identical in-phase amplitude component; andan identical bit layout, as available as possible from said bit layouts not assigned, is assigned to quadrature components at signal points having an identical quadrature amplitude component.11. A data transmission apparatus for sending transmission data in a 2 nQAM system (n is seven), comprising: a transmitter section; and a receiver section, said transmitter section comprising: an encoder with error correction for receiving said data as an input signal, for converting said data into an in-phase component signal and a quadrature component signal in a parallel signal form, the in-phase component signal and the quadrature component signal being orthogonal to each other, and for outputting the signals therefrom; anda modulator section for receiving the in-phase and quadrature component signals from said encoder with error correction, for generating an analog modulated wave signal using the in-phase and quadrature component signals, and for outputting the analog modulated wave signal therefrom; said receiver section comprising: a demodulator section for receiving the analog modulated wave signal from said transmitter section and for demodulating the analog modulated wave signal to generate an in-phase component signal and a quadrature component signal; anda decoder with error correction for receiving the in-phase component signal and the quadrature component signal from said demodulator section and for decoding the in-phase and quadrature component signals, wherein said encoder with error correction comprising: a converting section for converting said data into (n−1)-bit parallel data;a convolutional encoder for receiving one bit of the (n−1)-bit parallel data; anda signal point generator for receiving 2-bit data outputted from said convolutional encoder and data including remaining b its of the (n−1)-bit parallel data, wherein each of the 2-bit data from said convolutional encoder and said data including remaining bits of the (n−1)-bit parallel data is separated into an in-phase component and a quadrature component to be fed to said signal point generator, and wherein said signal point generator thereby generates a multilevel signal according to the 2 nQAM system which includes multilevel signals formed as below:in a signal point plane of an in-phase amplitude component(1)—quadrature amplitude component (Q) coordinate system, said plane is divided into a first area and a plurality of second areas;in the first area, an identical bit layout is assigned to in-phase components at signal points having an identical in-phase amplitude component and an identical bit layout is assigned to quadrature components at signal points having an identical quadrature amplitude component;in the second areas, bit layouts not assigned to the first area are assigned such that an identical bit layout to in-phase components at signal points having an identical in-phase amplitude component;in the first and second areas, mutually different bit values are assigned to the lowest bit of an in-phase component output from said convolutional encoder at signal points adjacent to each other in a direction of an in-phase component axis, regardless of each quadrant of I-Q coordinate system; and mutually different bit values are assigned to the lowest bit of a quadrature component output from said convolutional encoder at signal points adjacent to each other in a direction of a quadrature amplitude component axis, regardless of each quadrant of I-Q coordinate system; andfor quadrature components at signal points in the second areas, bits of bit layouts not assigned yet are assigned to bits other than bits equivalent to in-phase component outputs from said convolutional encoder; so that said signal points are independently assigned to each other in said in-phase components and said quadrature components in the direction of said in-phase and quadrature amplitude components axis, respectively, and each of said signal points according to said signals output from said convolutional encoder is assigned in an identical bit layout in each quadrant of I-Q coordinate system in the first and second areas. 12. A data transmission apparatus for sending transmission data in a 2 nQAM system (n is an even number equal to or more than four), comprising: a transmitter section; and a receiver section, said transmitter section comprising: an decoder with error correction for receiving said data as an input signal, for converting said data into an in-phase component signal and a quadrature component signal in a parallel signal form, the in-phase component signal and the quadrature component signal being orthogonal to each other, and for outputting the signals therefrom; anda modulator section for receiving the in-phase and quadrature component signals from said encoder with error correction, for generating an analog modulated wave signal using the in-phase and quadrature component signals, and for outputting the analog modulated wave signal therefrom; said receiver section comprising: a demodulator section for receiving the analog modulated wave signal from said transmitter section and for demodulating the analog modulated wave signal to generate an in-phase component signal and a quadrature component signal; anda decoder with error correction for receiving the in-phase component signal and the quadrature component signal from said demodulator section and for decoding the in-phase and quadrature component signals, wherein said encoder with error correction for use with 2 nQAM signals, an in-phase component signal and a quadrature component signal of said 2nQAM signals having mutually different bit values in a signal point plane of an in-phase amplitude component (I)—quadrature amplitude component (Q) coordinate system, re gardless of each quadrant of said I-Q coordinate system, comprising:an area deciding section for receiving the in-phase component(1)-signal and the quadrature component (Q) signal of the QAM signals, wherein said area deciding section decides, to which quadrant of a signal point plane of an in-phase amplitude component (I)—quadrature amplitude component (Q) coordinate system, said in-phase component (I) signal and said quadrature component (Q) signal belongs;first and second metric assigning sections for producing, based on the result of said area deciding section, metric for the in-phase component (I) and quadrature component (Q) signals, respectively;a Viterbi decoder for receiving the metrics for the in-phase component (I) and quadrature component (Q) signals;a convolutional encoder for receiving a data signal outputted from said Viterbi decoder;first and second decoders for being applied each of the in-phase component (I) and quadrature component (Q) signals from said area deciding section and said convolutional encoder, anda parallel/serial converter for receiving an output from said Viterbi decoder and outputs from said first and second decoders.13. A data transmission apparatus according to claim 12, wherein n is an even number equal to or more than four; said first decoder receives a data signal for said in-phase component signal from said convolutional encoder and the result from said area deciding section; and said second decoder receives a data signal for said quadrature component signal from said convolutional encoder and the result from said area deciding section, an output from said first decoder for the in-phase component signal, and output from said second decoder for the quadrature component signal, and the output from said Viterbi decoder are inputted to said parallel/serial converter. 14. A data transmission apparatus according to claim 12, wherein n is an odd number equal to or more than five; said first decoder receives a data signal for said in-phase component signal from said convolutional encoder and the results for said in-phase component signal and for said quadrature component signal from said area deciding section; said second decoder receives a data signal for the quadrature component signal and a data signal said in-phase component signal from said convolutional encoder, and the results of area decision for a quadrature component signal and for in-phase component signal from said area deciding section; and an output from said first decoder for an in-phase component, an output from said second decoder for a quadrature component signal, and the output from said Viterbi decoder are inputted to said parallel/serial converter. 15. A data transmission apparatus for sending data in a 2 nQAM system (n is an integer equal to or more than four), comprising: a converting section for converting said data into (n−1)-bit parallel data; a convolutional encoder for receiving one bit of the (n−1)-bit parallel data; a signal point generator for receiving 2-bit data outputted from said convolutional encoder and data including remaining bits of the (n 31 1)-bit parallel data, the 2-bit data from said convolutional encoder and the data of the remaining bits of the (n−1)-bit parallel data being separated, respectively, into an in-phase component signal and a quadrature component signal, in response to receiving the in-phase and quadrature component signals, said signal point generator generating multilevel signals according to the 2nQAM system; a modulator for receiving outputs from said signal point generator, said modulator modulating the in-phase and quadrature component signals respectively with modulating signals which are respectively orthogonal to the in-phase and quadrature component signals and each of which has a predetermined frequency, said modulating signals being added to each other; and a transmitting section for receiving an output from said modulator and for outputting a transmission signal, wherein the 2 nQAM system (n is an even number equal to or more than four) includes multilevel signals formed as below:in a signal point plane of an in-phase amplitude component (I)—quadrature amplitude component (Q) coordinate system, an identical bit layout is assigned to in-phase components at signal points having an identical in-phase amplitude component and an identical bit layout is assigned to quadrature components at signal points having an identical quadrature amplitude component;for in-phase components at signal points adjacent to each other in a direction of an in-phase amplitude component axis, mutually different bit value is assigned to the lowest bit—of an in-phase component outputs form said convolutional encoder, regardless of each quadrant of I-Q coordinate system;for quadrature components at signal points adjacent to each other in a direction of a quadrature amplitude component axis, mutually different bit value is assigned to the lowest bit of a quadrature component outputs from said convolutional encoder,so that said signal points are independently assigned to each other in said in-phase components and said quadrature components in the direction of said in-phase and quadrature amplitude components axis, respectively, and each of said signal points according to said signals output from said convolutional encoder is assigned in an identical bit layout in each quadrant of I-Q coordinate system in the first and second areas.16. A data transmission apparatus for sending data in a 2 nQAM system (n is an integer equal to or more than four), comprising: a converting section for converting said data into (n−1)-bit parallel data; a convolutional encoder for receiving one bit of the (n−1)-bit parallel data; a signal point generator for receiving 2-bit data outputted from said convolutional encoder and data including remaining bits of the (n−1)-bit parallel data, the 2-bit data from said convolutional encoder and the data of the remaining bits of the (n−1)-bit parallel data being separated, respectively, into an in-phase component signal and a quadrature component signal, in response to receiving the in-phase and quadrature component signals, said signal point generator generating multilevel signals according to the 2nQAM system; a modulator for receiving outputs from said signal point generator, said modulator modulating the in-phase and quadrature component signals respectively with modulating signals which are respectively orthogonal to the in-phase and quadrature component signals and each of which has a predetermined frequency, said modulating signals being added to each other; and a transmitting section for receiving an output from said modulator and for outputting a transmission signal, wherein the 2 nQAM system (n is an odd number equal to or more than five) includes multilevel signals as formed below:a signal point plane of an in-phase component (I)—quadrature amplitude component (Q) coordinate system is divided into a first area and a plurality of second areas;in the first area, an identical bit layout is assigned to in-phase components at signal points having an identical in-phase amplitude component and an identical bit layout is assigned to quadrature components at signal points having an identical quadrature amplitude component;in the first and second areas, mutually different bit values are assigned to the lowest bit of an in-phase component output from said convolutional encoder for signal points adjacent to each other in a direction of an in-phase amplitude component axis, regardless of each quadrant of I-Q coordinate system and mutually different bit values are assigned to the lowest bit of a quadrature component output from said convolutional encoder at signal points adjacent to each other in a direction of a quadrature amplitude component axis, regardless of each quadrant of I-Q coordinate system, bit arrays not assigned to the first area are assigned to signal points in the second areas; andmutually different bit layouts are assigned to respective signal points in the first and second areas,so that said signal points are independently assigned to each other in said in-phase components and said quadrature components in the direction of said in-phase and quadrature amplitude components axis, respectively, and each of said signal points according to said signals output from said convolutional encoder is assigned in an identical bit layout in each quadrant of I-Q coordinate system in the first and second areas.17. A data reception apparatus for receiving a multilevel signal in a 2 nQAM system (n is an integer equal to or more than four), comprising: a demodulator for demodulating the multilevel signal and for separating the multilevel signal into an in-phase component signal and a quadrature component signal; an automatic equalizer for receiving the in-phase component signal and the quadrature component signal and for automatically equalize the signals; a decision decoder for multilevel modulated signal in a 2 nQAM system (n is an integer equal to or more than four) including an area deciding section for receiving an in-phase component signal and a quadrature component signal of the 2nQAM system multilevel modulated signal, said area deciding section receiving the in-phase component signal (I) and the quadrature component (Q) signal of the QAM signals, said area deciding section deciding to which one of the areas each of the in-phase component (I) and quadrature component (Q) signals belongs; a metric assigning section for producing, according to a result of decision by said area deciding section, metric for each of the in-phase component (I) and quadrature component (Q) signals; a Viterbi decoder for receiving the metric for the in-phase component (I) and quadrature component (0) signals, a convolutional encoder for receiving a data signal outputted from said Viterbi decoder, and a decoder for receiving an output from said convolutional encoder; and a parallel/serial converter for receiving an output from said Viterbi decoder and outputs from said convolutional encoder. 18. A data reception apparatus according to claim 17, wherein: n is an even number equal to or more than four; said decoder further includes: a first decoder for receiving a data signal for an in-phase component from said convolutional encoder and a result of area decision for an in-phase component from said area deciding section; anda second decoder for receiving a data signal for a quadrature component from said convolutional encoder and a result of area decision for a quadrature component from said area deciding section,an output from said first decoder for an in-phase component, an output from said second decoder for a quadrature component, and the output from said Viterbi decoder are inputted to said parallel/serial converter.19. A data reception apparatus according to claim 17, wherein: n is an odd number equal to or more than five; said decoder further includes: a third decoder for receiving a data signal for an in-phase component and a data signal for a quadrature component from said convolutional encoder, and a result of area decision for an in-phase component and a result of area decision for a quadrature component from said area decision section; anda fourth decoder for receiving a data signal for a quadrature component and a data signal for an in-phase component from said convolutional encoder, and a result of area decision for a quadrature component and a result of area decision for an in-phase component from said area deciding section, an output from said third decoder for an in-phase component, an output from said fourth decoder for a quadrature component, and the output from said Viterbi decoder are inputted to said parallel/serial converter.