In this paper, we propose a computational algorithm of a pseudo-formal linearization method for nonlinear dynamic systems using the discrete Fourier series expansion in order to reduce computational burden. A nonlinear dynamic system is transformed into some augmented linear systems piecewisely with respect to a linearization function that consists of trigonometric functions by a pseudo-formal linearization method using the discrete Fourier series expansion. Then all of the linearized systems are smoothly united into a single linear system. As an application of this method, a computational algorithm for a nonlinear observer is also proposed. Numerical experiments are demonstrated to indicate the effectiveness of the proposed algorithms.
This paper proposes a multi-carrier (MC) modulation scheme employing differential trellis-coded modulation (DTCM) and multiple differential detection with channel prediction, in order to cope with doubly-selective fading at good required signal-to-noise power ratio (SNR), where doubly-selective channels correspond to severe time/frequency-selective channels. For frequency-selective fading, MC modulation schemes are effective. For time-selective fading, multiple differential detection employing per-survivor processing (PSP-MDD) with channel prediction is effective. However, channel prediction degrades the required SNR for PSP-MDD. In order to cope with doubly-selective fading and improve the required SNR, this paper proposes MC-DTCM employing PSP-MDD with channel prediction. Finally, computer simulation results show that the proposed scheme can improve both the performance for doubly-selective fading and the required SNR compared with the conventional PSP-MDD with channel prediction, and the proposed scheme is suitable for large-cell train radio communications.
This paper proposes differential orthogonal frequency division multiplexing (OFDM) employing automatic frequency control (AFC) for severe time and frequency selectivities, i.e., double selectivity in the presence of fast time-varying Doppler shifts. With respect to double selectivity, differential encoding/differential detection (DE/DD) is effective for time selectivity, and OFDM is effective for frequency selectivity. However, differential OFDM suffers from serious performance degradation due to intercarrier interference (ICI) caused by fast time-varying Doppler shifts. In order to cope with doubly-selective channels in the presence of fast time-varying Doppler shifts, this paper proposes differential OFDM employing AFC which can compensate frequency offset. The proposed scheme employs a multiple open-loop frequency estimation (MOLFE), which has a good trade-off between frequency coverage and estimation accuracy in short observation time. Next, this paper proposes a simple time-varying Doppler shift simulation model for autonomous underwater vehicle (AUV) turning. Finally, computer simulation results confirm that the proposed differential OFDM employing MOLFE has excellent performance in doubly-selective channels in the presence of fast time-varying Doppler shifts.
In this research note, we present an array lattice algorithm for H∞ adaptive filtering, in which pre-arrays are transformed into post-arrays by J-unitary transformations regarding an indefinite signature matrix J. The array form is derived by factorization with respect to an indefinite Hermitian matrix, which functionally corresponds to the so-called conversion factor in recursive least-squares algorithms. The numerical stability of the array lattice form in finite-precision arithmetic is verified by simulation in comparison with the standard H∞ filter implementation.
We showed that the partial reflection that simultaneously occurs with refraction can be analyzed by two methods, one introducing phase and amplitude and the other assuming electromagnetic waves, both of which obtain the same result. Both methods use the refractive index and reflection coefficient. In the method assuming electromagnetic waves, the refractive index and reflection coefficient are determined on the basis of the relationship between electric and magnetic fields, i.e., the physical properties of the electromagnetic waves. A space with electric and magnetic fields as two functions can be discussed in circuit theory, which implies an important application of circuit theory. Moreover, a resonant phenomenon is observed by the analysis of refraction and partial reflection. Waveforms with a predetermined angular frequency can be reconstructed and differ from those of harmonic oscillators discussed with electromagnetic waves. Thus, another important application of circuit theory is also shown in this session.