Spectrum Characteristics of Ternary PSK Signals Amplified with Non-Linear Amplifiers

Phase shift keying (PSK) is one of the most important classes of digital modulation schemes. M-ary PSK of which the value of M is other than the n-th power of 2 has not been focused on until now because it is not suitable for transmitting binary information. In a previous study, we reported that ternary PSK (TPSK) has theoretically the best error rate characteristic and the minimum instantaneous amplitude fluctuation among all of the PSK schemes. From the latter feature, it is surmised that the TPSK scheme can suppress unnecessary spectra caused by no-linear amplifiers. However, in order to clarify detailed effectiveness of this feature, it is necessary to evaluate spectrum characteristics of TPSK signals. In the present paper, the spectrum characteristics of the TPSK signals which are amplified with non-linear amplifiers after being inputted into a square root cosine roll-off filter are evaluated by computer simulation. The results show that the spectrum characteristic of the TPSK signal is superior to that of QPSK signal and that of π /4 shift QPSK signal. Key-Words: Digital modulation, Phase shift keying (PSK), Ternary PSK (TPSK), Spectrum characteristic, Non-linear amplifier, Square root cosine roll-off filter