We are studying 16APSK and 32APSK, which can transmit more HDTV programs per channel or be applied for high quality services beyond HDTV. Multi-level modulations such as these APSK schemes are vulnerable to the non-linear distortion of a satellite transponder. We propose a compensation technique for estimating the signal point error vectors over a satellite simulator in advance and compensating for the error vectors of each signal point at the transmitter. We report on both 16APSK and 32APSK performances in terms of the required C/N and optimum operating point of the traveling wave tube amplifier (TWTA) by using a computer simulation on the effect of this compensation technique.

We propose an equalization technique that uses the characteristics of the satellite transponder to compensate for its non-linear distortion. In our previous study, the effects of this technique for 16APSK and 32APSK were assessed in simulations. In this study, we revised the configuration of the equalization system and developed a receiver based on this revision. We examined the reception performance of 16APSK and 32APSK in transmission experiments.

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We propose two van der Pol oscillators with high-order nonlinearities coupled with an inductor and investigate various types of multimode oscillations. We confirm that these oscillations are stably excited by numerical calculations, theoretical analyses and circuit experiments. In particular, we aim to show relations between the multimode oscillations and the number of order nonlinear characteristics.

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