Abstract
Continuous phase modulation (CPM) has constant envelope and good spectral properties; therefore, it is suitable for satellite communication systems that require high power amplifiers. In addition, these properties are suitable for limited power systems such as sensor devices. On the other hand, recent broadband mobile communication systems use space time block codes (STBCs) to obtain channel gain using multiple antennas. STBC-CPM is a combination of STBC and CPM, having the advantages of both techniques. A purpose of this study is to establish STBC-CPM system which has spectral efficiency and power efficiency at the same time. In this paper, we compare the spectral efficiency of STBC-CPM with two and four transmit antennas. We especially consider the relationship between modulation parameters and spectral efficiency in detail. We also propose to use quasi orthogonal-STBC (QO-STBC) so as to improve spectral efficiency. From simulation results, we found that an improvement in the spectral efficiency by 0.5 bit/s/Hz can be achieved by using QO-STBC. The results are useful for designing STBC-CPM for future satellite communication systems or sensor network systems.