NOLTA publishes a series of Invited Review papers contributed from outstanding researchers.
You will find good articles to gain comprehensive knowledge useful to overlook research fields of your own interests.
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Haruna Matsushita, Hiroaki Kurokawa, Takuji Kousaka,
Bifurcation analysis by particle swarm optimization
vol. 11, no. 4, pp. 391-408, October 2020
DOI: https://doi.org/10.1587/nolta.11.391
Abstruct:
This paper explains a bifurcation parameter detection strategy based on particle swarm optimization (PSO),
and it shows application examples on detection of local bifurcation parameters appearing in discrete-time dynamical
systems and non-autonomous continuous dynamical systems. The algorithm design and analysis part shows that the PSO-based
algorithm is fairly simple, easily understandable, and easily implementable. The method requires no careful initialization,
exact calculation, gradient information of the system, or Lyapunov exponents.
However, the simulation results show that the method accurately detects the local bifurcation parameters regardless of
the stability of the periodic point.
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Toshimichi Saito,
Piecewise linear switched dynamical systems: A review
vol. 11, no. 4, pp. 373-390, October 2020
DOI: https://doi.org/10.1587/nolta.11.373
Abstruct:
This review paper introduces piecewise linear switched dynamical systems in three topics.
In the first topic of autonomous chaotic circuits, we introduce the manifold piecewise linear system and chaotic spiking
oscillator. Using piecewise exact solutions and mapping procedure, we obtain rigorous proof of chaos generation.
In the second topic of recurrent neural networks, we introduce the hysteresis neural network and its application to
associative memories. Performing theoretical analysis based on the piecewise exact solutions, we obtain parameter
conditions for guaranteed storage of any desired memories. In the third topic of multiobjective optimization problems,
we introduce a two-objective problem in a piecewise linear model of switching power converter with photovoltaic input.
Applying a simple multiobjective evolutionary algorithm, we clarify existence of a trade-off between the maximum input
power and circuit stability.
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Yoshiki Sugitani, Keiji Konishi,
Delay-induced stabilization of coupled oscillators
vol. 12, no. 4, pp. 612-624, October 2021
DOI: https://doi.org/10.1587/nolta.11.373
Abstruct:
Delays can have a negative impact on the stability of various systems.
However, it was reported that the transmission delays of signals among oscillators can stabilize unstable
equilibrium points in coupled oscillators, which is called amplitude death (AD).
AD caused by delays has been extensively researched in the field of nonlinear science and has attracted attention
for various engineering applications. In this article, we review the latest studies on AD caused by delays in oscillator
networks, in particular those that considered heterogeneous delays and time-varying networks.
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Kenya Jin'no,
Analysis of particle swarm optimization by dynamical systems theory
vol. 12, no. 2, pp. 118-132, April 2021
DOI: https://doi.org/10.1587/nolta.12.118
Abstruct:
Particle Swarm Optimization (PSO) is one of the most effective optimization methods for the black-box optimization
problem. PSO involves a large number of particles sharing information with each other to search for the optimal solution.
The method in which a large number of search individuals cooperate to search for the optimal solution is called swarm
intelligence optimization. In the group intelligence optimization, the balance between exploration and exploitation is
important. However, in PSO, it is unclear to what extent each parameter affects exploration and exploitation. Therefore,
we proposed a deterministic PSO without probabilistic elements and analyzed the dynamics of PSO using dynamical systems
theory. Each particle in deterministic PSO has its motion determined by its eigenvalue. In order to make this motion
clearer, a canonical deterministic PSO on a regularized phase space was proposed. The results of these analyses clarified
what is attributed to the parameters for exploration and exploitation, i.e., global and local search capabilities.
Based on this fact, we proposed a nonlinear map optimization (NMO) with improved local search capability. In this paper,
we present the background of our proposal and consider the solution-search capability of nonlinear map optimization.
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Hiroyuki Asahara, Takuji Kousaka,
Stability analysis based on monodromy matrix for switched dynamical systems
vol. 12, no. 3, pp. 237-256, July 2021
DOI: https://doi.org/10.1587/nolta.12.237
Abstruct:
This study reports a stability analysis method based on the monodromy matrix for switched dynamical systems.
First, we focus on nonlinear autonomous interrupted systems. In the electrical field, for example, most circuit
equations are described in the form of a linear ordinary differential equation. However, with the growth of clean
energy power generation devices, the nonlinear term appears in the circuit equation as represented by the photovoltaic
module. From this point of view, we discuss a stability analysis method based on the monodromy matrix for nonlinear
interrupted systems. Second, we consider impacting systems with a periodic threshold. The previous stability analysis
method based on the monodromy matrix is only applicable to impacting systems with fixed threshold. We improved this
method considering the periodic threshold. Many impacting systems in the engineering field have a periodic threshold;
hence, we introduce this method herein with a mechanical application example. We aim to contribute to the development
of the nonlinear theory using above-mentioned two topics.
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Eiji Okamoto,
Overview of nonlinear signal processing in 5G and 6G access technologies
vol. 12, no. 3, pp. 257-274, July 2021
DOI: https://doi.org/10.1587/nolta.12.257
Abstruct:
In recent years, there have been several advances in wireless communication systems, including the increase in
transmission rate, and as a result, they are playing an increasingly significant role in our lives. To meet the
widespread application scope, the commercialization of the fifth-generation mobile communications system (5G)
has been initialized. This paper gives an overview of the 5G system and discusses the nonlinear signal processing
technologies that support its performance improvement. Here, the term “nonlinear signal processing” is defined as an
algorithm for transmitting and receiving data in communications that uses a nonlinear mechanism. Because there is a
significant shortage of frequency bands in wireless communications, advanced technologies are being integrated to
maximize frequency utilization. In addition, unlike in the 4G era, there are additional use cases that require
performance guarantees for quality, delay, and the number of multiple connections in the 5G system, and the performance
requirements for wireless systems are becoming more stringent. Nonlinear signal processing is key to improving the
performance of these systems, and this paper outlines the nonlinear technology used in 5G wireless access. We will
introduce multiple-input multiple-output transmission and non-orthogonal multiple access (NOMA), which will help
improve the performance of wireless systems. In addition, we introduce a radio wave-encrypted NOMA with a physical
layer security that is proposed by the authors. Furthermore, the technical trend of 6G is briefly introduced.
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Kosuke Sanada,
Theoretical analysis for CSMA/CA-based wireless full duplex networks
vol. 12, no. 3, pp. 275-293, July 2021
DOI: https://doi.org/10.1587/nolta.12.275
Abstruct:
Full Duplex (FD) communication can potentially double the throughput of a point-to-point link in wireless
communication. Additionally, FD communication can mitigate collisions induced by hidden nodes. Though exchanging
control frames also mitigate hidden node collisions, FD communication has a smaller overhead for one data transmission
than the control-frame scheme. Although FD communication is expected to provide system-performance improvement, the
enhancement highly depends on its network topology or system parameters. Besides, it is not easy work to comprehend
the relationships between system parameters and network performance. Theoretical analysis is useful for evaluating
network performance and the optimal design for the system. This paper introduces theoretical analysis for Carrier Sense
Multiple Access with Collision Avoidance (CSMA/CA)-based wireless FD networks, mainly author's researches, and
discusses their performance. In this paper, star-topology single-hop networks and string topology multi-hop networks
are considered as analysis subjects. This paper evaluates FD communication potential for each network through the
analytical model by comparing network performances with exchanging control frames and FD communication.
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Atsuo Maki, Yuu Miino, Naoya Umeda, Masahiro Sakai, Tetsushi Ueta, Hiroshi Kawakami,
Nonlinear dynamics of ship capsizing at sea
vol. 13, no. 1, pp. 2-24, January 2022
DOI: https://doi.org/10.1587/nolta.13.2
Abstruct:
Capsizing is one of the worst scenarios in oceangoing vessels. It could lead to a high number of fatalities.
A considerable number of studies have been conducted until the 1980s, and one of the discoveries is the weather
criterion established by the International Maritime Organization (IMO). In the past, one of the biggest difficulties
in revealing the behavior of ship-roll motion was the nonlinearity of the governing equation. On the other hand, after
the mid-1980s, the complexity of the capsizing problem was uncovered with the aid of computers. In this study,
we present the theoretical backgrounds of the capsizing problem from the viewpoint of nonlinear dynamics. Then, we
discuss the theoretical conditions and mechanisms of the bifurcations of periodic solutions and numerical attempts
for the bifurcations and capsizing.
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Tomoyuki Sasaki, Hidehiro Nakano,
Piecewise-linear particle swarm optimizer, basic dynamics, reference frame invariance, and search performance
vol. 13, no. 2, pp. 170-195, April 2022
DOI: https://doi.org/10.1587/nolta.13.170
Abstruct:
Swarm intelligence (SI) algorithms have been studied in solving real-world optimization problems called black-box
optimization problems. Typical features of SI algorithms are: (1) being a population-based metaheuristics;
(2) using fitness values of a given objective function; and (3) having very simple search rules which search agents
follow. As such, SI algorithms have been applied to various black-box optimization problems. Particle swarm
optimization is one of powerful SI algorithms, in which a swarm consists of plural particles as solution candidates.
Particles directly fly a search space and share their own information each other, and thus PSO can find good quality
of solutions. However, a PSO swarm is easily stuck in solving optimization problems whose search space is
high-dimensional and complicated. In order to solve such problems, large numbers of particles and reference frame
invariance are needed for PSO algorithms. Herein, we suggest a piecewise-linear particle swarm optimizer (PPSO)
which is a deterministic PSO. PPSO has two simple search modes switched to another mode dynamically, whose search
dynamics are complex. As such, PPSO algorithm can be implemented on hardware with low hardware costs because PPSO
algorithm must not require many random number generators. In addition, PPSO algorithm can find a good quality of
solution in solving complex optimization problems. We studied search performances of PPSO compared to PSO algorithms
and provide theoretical analysis of reference frame invariance for PPSO. In order to verify search performances and
theoretical analysis, we performed numerical simulations.
