This paper presents development of a quad rotor tail-sitter VTOL UAV (Vertical Takeoff and Landing Unmanned Aerial Vehicle) which is composed of four rotors and a fixed wing. The conventional VTOL UAVs have a drawback in the accuracy of the attitude control in stationary hovering because they were developed based on a fixed-wing aircraft and they used the control surfaces, such as aileron, elevator, and rudder for the attitude control. To overcome such a drawback, we developed a quad rotor tail-sitter VTOL UAV. The quad rotor tail-sitter VTOL UAV realizes high accuracy in the attitude control with four rotors like a quad rotor helicopter and achieves level flight like a fixed-wing airplane. The remarkable characteristic of the developed quad rotor tail-sitter VTOL UAV is that it does not use any control surfaces even in the level flight. This paper shows the design concept of the developed UAV and experimental verification of all flight modes including hovering, transition flight and level flight.

In this paper the performance of the mixed-base modulation (MBM) system is analyzed for the case where the input signal is a sample function of a Gaussian random process and an optimum stretching is employed. The comparison of theoretical performance of the MBM system with that of other common modulation schemes such as FM and PCM/PSK shows that it provides performance much better than that of those schemes where the same bandspread factor is employed.

Upper and lower bounds on the probability of error of binary CPSK system subject to additive non-Gaussian noise and intersymbol interference are derived and the bounds are evaluated for square-wave signaling when the signal is pasSed through filters of Butterworth and Chebyshev transmission characteristics. It is assumed that the distribution of the non-Gaussian noise is characterized by skewness and kurtosis. These parameters express the effect of the limiter on the channel noise. For square-wave signaling it is shown that the skewness has no effect on the performance of the system, and it is also shown that the kurtosis always degrades the probability of error of the system and it increases linearly with the kurtosis.

In this correspondence, first it is pointed out that introducing time delay of one sampling interval in digital phase-locked loop considerably eases restriction on operating times of digital circuits in the loop. Then statistical analyses are performed for first- and secondorder loops with time delay of one sampling interval in order to see the effect of the time delay on their performances. Approximate analytic expressions are obtained for the steady-state phase error probability density and phase error variance, and their validity is confirmed by numerical analysis. Increase in the phase error variance due to the introduction of the time delay is found to be of tolerable order for sufficiently high input SNR, and thus the delayed sampling scheme proposed here is considered to be effective in easing the restriction on the operating times of the digital circuits in the loop.