Spatially Superposed Highly Efficient 32APSK Transmission System

Abstract

A highly efficient 32 amplitude phase-shift keying (APSK) modulation satellite broadband communication system is presented here that improves the usage efficiency of the frequency resources and energy. It features a two-beam spatial superposition. The system incorporates an 8 phase-shift keying (8PSK) modulator, a quaternary phase-shift keying (QPSK) modulator, and multiple high power amplifiers (HPAs) that operate in their nonlinear region at a high level of efficiency. The lower amplitude change for the 8PSK and QPSK signals enables the HPAs in the proposed system to operate in the nonlinear high efficiency region, in which conventional systems, such as 4+12+16 APSK or 32 quadrature amplitude modulation (QAM) systems, cannot operate. After being power-amplified, their output signals are spatially superposed using a specially tailored antenna to produce a new 8x4= 32APSK signal. We investigated the performance of the new 32APSK system and found that it had a better bit error rate (BER) than the conventional 32APSK system when operated in the HPA nonlinear high efficiency region. The results from a theoretical transmission analysis helped to determine the acceptable timing delay between two modulators and the spatial superposition errors. In addition, a high gain antenna system suitable for combining the two beams is presented that satisfies the acceptable superposition errors. We also performed some experiments and proved that the spatial superposed 32APSK system is feasible and that it consumes 50% less HPA power than the 4+12+16 APSK system. Thus, the proposed system is feasible and will enable broadband transmission while more efficiently using the available amount of energy and bandwidth.