Method for modulation and transmission apparatus
An input digital signal is periodically and alternately subjected to first modulation and second modulation, being thereby converted into a pair of a baseband I signal and a baseband Q signal. The first modulation and the second modulation are different from each other. The pair of the baseband I signal and the baseband Q signal are outputted. The first modulation may be at least 8-signal-point modulation while the second modulation may be phase shift keying.
1. A method for modulation, comprising the steps of:
regularly subjecting an input digital signal to first modulation and second modulation to convert the input digital signal into a pair of a baseband I signal and a baseband Q signal, the first modulation and the second modulation being different from each other; and
outputting the pair of the baseband I signal and the baseband Q signal;
wherein the first modulation is at least 8-signal-point modulation, and the second modulation is phase shift keying;
wherein the phase shift keying provides periodically-spaced symbols which represent corresponding portions of the input digital signal in terms of differences between phases of the periodically-spaced symbols; and
wherein the at least 8-signal-point modulation assigns logic states of the input digital signal to respective signal points for a first symbol in response to a signal point used by a second symbol of the phase shift keying which precedes the first symbol.
2. A method as recited in claim 1 , wherein the phase shift keying is quadrature phase shift keying.
3. A method as recited in claim 2 , wherein the quadrature phase shift keying provides signal points on an I axis and a Q axis in an I-Q plane.
4. A method as recited in claim 1 , wherein the at least 8-signal-point modulation is at least 8 quadrature amplitude modulation.
5. A method as recited in claim 3 , wherein the at least 8-signal-point modulation is at least 8 quadrature amplitude modulation.
6. A method as recited in claim 4 , wherein at least 8 quadrature amplitude modulation is 16 quadrature amplitude modulation.
7. A method as recited in claim 5 , wherein the at least 8 quadrature amplitude modulation is 16 quadrature amplitude modulation.
8. A method as recited in claim 4 , wherein the at least 8 quadrature amplitude modulation provides signal points which result from rotation of signal points of at least 8-value normal quadrature amplitude modulation through an angle of π/4 radian about an origin in an I-Q plane.
9. A method as recited in claim 5 , wherein the at least 8 quadrature amplitude modulation provides signal points which result from rotation of signal points of at least 8-value normal quadrature amplitude modulation through an angle of π/4 radian about an origin in an I-Q plane.
10. A method as recited in claim 6 , wherein the 16 quadrature amplitude modulation provides signal points which result from rotation of signal points of 16-value normal quadrature amplitude modulation through an angle of π/4 radian about an origin in an I-Q plane.
11. A method as recited in claim 7 , wherein the 16 quadrature amplitude modulation provides signal points which result from rotation of signal points of 16-value normal quadrature amplitude modulation through an angle of π/4 radian about an origin in an I-Q plane.
12. A method as recited in claim 1 , wherein a maximum of amplitudes corresponding to signal points of the at least 8-signal-point modulation in an I-Q plane is equal to an amplitude of a signal point of the phase shift keying in the I-Q plane.
13. A transmission apparatus comprising:
first means for periodically and alternately subjecting an input digital signal to first modulation and second modulation to convert the input digital signal into a pair of a baseband I signal and a baseband Q signal, the first modulation and the second modulation being different from each other, the first modulation being at least 8-signal-point modulation, the second modulation being phase shift keying;
second means for outputting the pair of the baseband I signal and the baseband Q signal;
wherein the phase shift keying provides periodically-spaced symbols which represent corresponding portions of the input digital signal in terms of differences between phases of the periodically-spaced symbols;
wherein the at least 8-signal-point modulation assigns logic states of the input digital signal to respective signal points for a first symbol in response to a signal point used by a second symbol of the shift keying which precedes the first symbol; and
wherein said first symbol is demodulated by using said second symbol which is not a known prescribed pattern but a part of information transmitted by said transmission apparatus.
14. A transmission apparatus as recited in claim 13 , wherein the symbols provided by the phase shift keying are used as a pilot symbol for estimating at least one of (1) a transmission path distortion and (2) a frequency offset.
15. A method for modulation, comprising the steps of: regularly subjecting an input digital signal having different transmission timings to first modulation and second modulation, respectively, to convert the input digital signal having different transmission timings into a pair of a baseband I signal and a baseband Q signal, the first modulation and the second modulation being different from each other; and outputting the pair of the baseband I signal and the baseband Q signal; wherein the first modulation is at least 8-signal-point modulation, and the second modulation is phase shift keying; wherein the phase shift keying provides periodically-spaced symbols which represent corresponding portions of the input digital signal in terms of differences between phases of the periodically-spaced symbols; and wherein the at least 8-signal-point modulation assigns logic states of the input digital signal having different transmission timings to respective signal points for a first symbol in response to a signal point used by a second symbol of the phase shift keying which precedes the first symbol.
16. A method as recited in claim 15, wherein the phase shift keying is quadrature phase shift keying.
17. A method as recited in claim 16, wherein the quadrature phase shift keying provides signal points on an I axis and a Q axis in an I-Q plane.
18. A method as recited in claim 15, wherein the at least 8-signal-point modulation is at least 8 quadrature amplitude modulation.
19. A method as recited in claim 17, wherein the at least 8-signal-point modulation is at least 8 quadrature amplitude modulation.
20. A method as recited in claim 18, wherein at least 8 quadrature amplitude modulation is 16 quadrature amplitude modulation.
21. A method as recited in claim 19, wherein the at least 8 quadrature amplitude modulation is 16 quadrature amplitude modulation.
22. A method as recited in claim 18, wherein the at least 8 quadrature amplitude modulation provides signal points which result from rotation of signal points of at least 8-value normal quadrature amplitude modulation through an angle of π/4 radian about an origin in an I-Q plane.
23. A method as recited in claim 19, wherein the at least 8 quadrature amplitude modulation provides signal points which result from rotation of signal points of at least 8-value normal quadrature amplitude modulation through an angle of π/4 radian about an origin in an I-Q plane.
24. A method as recited in claim 20, wherein the 16 quadrature amplitude modulation provides signal points which result from rotation of signal points of 16-value normal quadrature amplitude modulation through an angle of π/4 radian about an origin in an I-Q plane.
25. A method as recited in claim 21, wherein the 16 quadrature amplitude modulation provides signal points which result from rotation of signal points of 16-value normal quadrature amplitude modulation through an angle of π/4 radian about an origin in an I-Q plane.
26. A method as recited in claim 15, wherein a maximum of amplitudes corresponding to signal points of the at least 8-signal-point modulation in an I-Q plane is equal to an amplitude of a signal point of the phase shift keying in the I-Q plane.
27. A transmission apparatus comprising: first means for periodically and alternately subjecting an input digital signal having different transmission timings to first modulation and second modulation, respectively, to convert the input digital signal having different transmission timings into a pair of a baseband I signal and a baseband Q signal, the first modulation and the second modulation being different from each other, the first modulation being at least 8-signal-point modulation, the second modulation being phase shift keying; second means for outputting the pair of the baseband I signal and the baseband Q signal; wherein the phase shift keying provides periodically-spaced symbols which represent corresponding portions of the input digital signal in terms of differences between phases of the periodically-spaced symbols; wherein the at least 8-signal-point modulation assigns logic states of the input digital signal having different transmission timings to respective signal points for a first symbol in response to a signal point used by a second symbol of the shift keying which precedes the first symbol; and wherein said first symbol is demodulated by using said second symbol which is not a known prescribed pattern but a part of information transmitted by said transmission apparatus.
28. A transmission apparatus as recited in claim 27, wherein the symbols provided by the phase shift keying are used as a pilot symbol for estimating at least one of (1) a transmission path distortion and (2) a frequency offset.
29. A method as recited in claim 15, wherein the at least 8-signal-point modulation assigns logic states of corresponding portions of the input digital signal to respective signal points for said first symbol in response to the signal point used by said second symbol of the phase shift keying, by changing phase components of modulation signal points for said first symbol on an I-Q plane in response to the signal point used by said second symbol, wherein each of the modulation signal points is composed of a phase component and an amplitude component.
30. A method as recited in claim 15, wherein the signal point used by said second symbol of the phase shift keying is a signal point arranged on an I axis or a Q axis of an I-Q plane.
31. An apparatus as recited in claim 27, wherein the phase shift keying is quadrature phase shift keying.
32. An apparatus as recited in claim 31, wherein the quadrature phase shift keying provides signal points on an I axis and a Q axis in an I-Q plane.
33. An apparatus as recited in claim 27, wherein the at least 8-signal-point modulation is at least 8 quadrature amplitude modulation.
34. An apparatus as recited in claim 33, wherein the at least 8 quadrature amplitude modulation is 16 quadrature amplitude modulation.