Masanobu Kominami

Blind phase recovery in QAM communication systems using higher order statistics

We present a method for phase recovery in QAM communication systems based on higher order statistics. Under the assumption that the QAM signals have independent, identically distributed (i.i.d.) in-phase and quadrature components, we derive the relation between the phase error and the fourth-order cumulant of the output. Numerical performance of the approach is demonstrated by computer simulation.

Blind identification of noncausal AR models based on higher-order statistics

Abstract In this paper we develop a new method to identify noncausal AR models that are driven by non-Gaussian i.i.d. input. Under a few moderate assumptions, the necessary and sufficient conditions for rebuilding the AR models from second and third order statistics are derived. It is shown that the AR model parameters are directly related to the solution of an eigenproblem. Based on this approach we present a method of AR model identification, applying eigendecomposition. Unique identification of AR models is guaranteed up to sign and linear phase ambiguities. Model order determination is not crucial in the method. If the order is overestimated, several equivalent AR models with different linear phases will be obtained.

Performance improvement of CDMA/QPSK systems with nonlinear channel using decision feedback equalizers

This paper proposes an improvement method of the performance characteristics of a quadriphase phase-shift-keyed code-division multiple-access (CDMA/QPSK) system with a nonlinear channel such as a satellite repeater which consists of a traveling-wave tube (TWT). Two adaptive decision feedback equalizers are used to improve the system performance degraded by the nonlinear channel. From calculation results, it is shown that the degradations are improved considerably.

An analysis of nonlinear distortion due to TWT in asynchronous DS-SSMB communication systems

We analyze the effects of the amplitude nonlinearity and AM/PM conversion in a traveling wave tube (TWT) used in an asynchronous direct sequence spread spectrum multiple access (DS-SSMA) communication system, assuming that the nonlinearity is represented by the power series of the input signal and the conversion is relatively small. We propose an analytical method of the signal-to-noise ratio at the output of the correlation detector in the receiver. We also justify our method by comparing the theoretic results with the computer simulations in when the amplitude nonlinear circuit is modeled by an error function as a typical example and show that the third order intermodulation product can be almost neglected in the sense of the signal-to-noise ratio.<<ETX>>

An improvement of nonlinear characteristics in DS-SSMA communication systems using equalizers

This paper proposes an improvement method of the deteriorated characteristics on account of the nonlinearity in direct sequence spread spectrum multiple access (DS-SSMA) communication systems. Where, a traveling wave tube (TWT) is adopted as nonlinear circuit in which the amplitude nonlinearity and AM/PM conversion are assumed to be relatively small. The transmission signal is expressed in two quadrature components and an equalizer of feed-forward transversal type is used to improve the nonlinear characteristics. The calculation results show that the significant improvement can be obtained from a simple equalizer using the least mean square algorithm.

A computer-aided design of EMC microstrip dipole arrays using nonlinear optimization techniques

This paper describes a method for designing electromagnetically coupled (EMC) printed dipole arrays. The advantages of EMC dipoles include greater bandwidth, higher efficiency, and an easier match to the feed lines, when compared to classically fed printed antennae. The excitation mechanism is provided by a strip transmission line embedded inside the substrate which couples energy parasitically to the microstrip antenna. Electromagnetically coupled microstrip dipoles have been investigated by empirical or approximate analysis techniques. As a result an approximate model has been derived for microstrip dipoles. The method is based on the method of moments solution to an integral equation derived from the approximate Green function for a grounded dielectric slab. The element lengths and offsets and the stub length of the EMC dipole array are determined by the direct search optimization method of Hooke and Jeeves. To show the feasibility of the proposed method, a mathematical formulation and numerical results are presented for Chebyshev arrays.

An effect of a DS-SSMA system on narrow-band communication systems using frequency region in common and its rejection method

When a DS-SSMA communication system uses in common the frequency region which narrow-band communication systems have used, the interference power falling on the narrow-band systems from the SS system should be considered. We propose a method that rejects the interference signal component on the transmitting side of the SS system and the transmission signals of the narrow-band systems on the receiving side of the SS system. We clarify the relationship between the signal-to-noise power ratio of the SS system with these band rejection filters and the ratio of narrow bandwidth to the chip rate, and show that prediction error filters are useful to the rejection filters.<<ETX>>