This paper presents a pseudo-formal linearization method based on the polynomial approximation for nonlinear systems. The given nonlinear system which is expressed by the ordinary differential equation is piecewisely linearized with respect to an augmented linearization function which consists of polynomials by the formal linearization approach. Then each linearized system is smoothly united into a single linear one by an automatic choosing function. This method is making use of Taylor expansion as the basis and Chebyshev interpolation as a faster calculation of linearization. As an application of this method, a nonlinear observer is designed to estimate the states of an electric power system. Numerical experiments show the effectiveness of this method.

This paper presents asynchronous demodulation methods without the threshold effect for a single sideband (SSB) with reduced carrier signal propagating through mobile radio paths. After an SSB with reduced carrier signal is converted into real zero SSB (RZ SSB) signals in a receiver, the relation of a Hilbert transform pair plays the main role in obtaining its practically perfect demodulation performance using DSP (Digital Signal Processing) processors. The asynchronous demodulation method, first developed in this study, is indispensable for supporting ‘burst mode transmission’ using SSB technology for voice/digital data communications with an ITU-T (International Telecommunication Union Telecommunication Standardization Sector) voiceband modem (MOdulator-DEModulator).

This paper is concerned with a pseudo-formal linearization method using the Fourier series expansion. The given nonlinear dynamic system is piecewisely linearized into some augmented linear systems with respect to a linearization function that consists of the state variables and their trigonometric functions. The resulting linear systems are smoothly united into a single system. Its application to a nonlinear observer and numerical examples are also included.

In this paper, we propose a time difference of arrival (TDOA) measurement algorithm resistant to multipath interference in estimating direction of arrival (DOA) of an underwater sound source. In strong multipath interference, the pseudo-peaks caused by reflected affect the correlation function, which makes it difficult to detect the peak with correct time position and leads to a large TDOA measurement error. The proposed method detects the arrival time difference by cross-correlating two impulse responses measured using a reference signal, and realizes a TDOA measurement that is resistant to multipath interference. We discuss the effectiveness of the proposed method by using an underwater acoustic reflection model, and report its performance by comparing the conventional method and the proposed method by our simulation and experiment.

The Winograd small fast Fourier transform (FFT) is a method of efficiently computing the discrete Fourier transform (DFT) for data of small block length. The equations of post-additions, constant multiplication factors, and pre-additions for the Winograd 9-point FFT are given in references [3], [5], [6]. A 6 × 6 block matrix is obtained from 9-point DFT matrix by matrix manipulation. By using the 6 × 6 block matrix, 3 × 3 circular and quasi-circular matrices can be derived. New identical equations for 3 × 3 circular and quasi-circular matrices have been derived by the authors. A new simple algorithm is given for the Winograd 9-point FFT correctly by using new identical equations for 3 × 3 circular and quasi-circular matrices.