Signal generating method and signal generating apparatus
A transmission method for simultaneously transmitting a first modulated signal and a second modulated signal at the same frequency includes performing precoding on both signals using a fixed precoding matrix and regularly changing the phase of at least one of the signals. In this method, the power ratio between a plurality of signals transmitted from a plurality of antennas at the same frequency and at the same time differs from the power ratio between a plurality of pilot signals transmitted from the plurality of antennas at the same frequency and at the same time, whereby the accuracy of channel estimation by a reception device is improved.
1. A transmission apparatus comprising:
a first modulator that generates a first modulation signal by modulating a first data sequence with a first modulation scheme;
a second modulator that generates a second modulation signal by modulating a second data sequence with a second modulation scheme which has an amount of signal points greater than the first modulation scheme, an average transmission power of the second modulation signal being the same as an average transmission power of the first modulation signal;
a power adjuster that (i) adjusts an amplitude of the first modulation signal and (ii) adjusts an amplitude of the second modulation signal;
a pre-coder that (i) generates a first pre-coding signal using the adjusted first modulation signal and the adjusted second modulation signal with a predetermined pre-coding matrix and (ii) generates a second pre-coding signal using the adjusted first modulation signal and the adjusted second modulation signal with the predetermined pre-coding matrix;
a first transmitter transmits the first pre-coding signal from a first antenna at a first time and a first frequency; and
a second transmitter transmits the second pre-coding signal from a second antenna at the first time and the first frequency, wherein
a second minimum distance between each signal point of the adjusted second modulation signal on an I-Q plane is shorter than a first minimum distance between each signal point of the adjusted first modulation signal on an I-Q plane.
2. The transmission apparatus according to claim 1 , wherein
the power adjuster adjusts (i) the amplitude of the second modulation signal so as to be longer and (ii) the amplitude of the first modulation signal so as to be shorter.
3. The transmission apparatus according to claim 1 , wherein
the first modulation scheme is Quadrature Phase Shift Keying (QPSK), and
the second modulation scheme is 16-Quadrature Amplitude Modulation (QAM).
4. The transmission apparatus according to claim 1 , wherein
the first modulation scheme is QPSK, and
the second modulation scheme is one of 16-QAM and 64-QAM.
5. The transmission apparatus according to claim 1 , wherein
the power adjuster adjusts the amplitude of the first modulation signal by multiplying the first modulation signal by a first real number corresponding to the first modulation scheme, and
the power adjuster adjusts the amplitude of the second modulation signal by multiplying the second modulation signal by a second real number corresponding to the second modulation scheme.
6. A transmission method comprising:
generating a first modulation signal by modulating a first data sequence with a first modulation scheme;
generating a second modulation signal by modulating a second data sequence with a second modulation scheme which has an amount of signal points greater than the first modulation scheme, an average transmission power of the second modulation signal being the same as an average transmission power of the first modulation signal;
adjusting an amplitude of the first modulation signal;
adjusting an amplitude of the second modulation signal;
generating a first pre-coding signal using the adjusted first modulation signal and the adjusted second modulation signal with a predetermined pre-coding matrix;
generating a second pre-coding signal using the adjusted first modulation signal and the adjusted second modulation signal with the predetermined pre-coding matrix;
transmitting the first pre-coding signal from a first antenna at a first time and a first frequency; and
transmitting the second pre-coding signal from a second antenna at the first time and the first frequency, wherein
a second minimum distance between each signal point of the adjusted second modulation signal on an I-Q plane is shorter than a first minimum distance between each signal point of the adjusted first modulation signal on an I-Q plane.
7. The transmission method according to claim 6 , wherein
the amplitude of the second modulation signal is adjusted so as to be longer, and the amplitude of the first modulation signal is adjusted so as to be shorter.
8. The transmission method according to claim 6 , wherein
the first modulation scheme is QPSK, and
the second modulation scheme is 16-QAM.
9. The transmission method according to claim 6 , wherein
the first modulation scheme is QPSK, and
the second modulation scheme is one of 16-QAM and 64-QAM.
10. The transmission method according to claim 6 , wherein
the amplitude of the first modulation signal is adjusted by multiplying the first modulation signal by a first real number corresponding to the first modulation scheme, and
the amplitude of the second modulation signal is adjusted by multiplying the second modulation signal by a second real number corresponding to the second modulation scheme.