Takashi Ohira

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We describe a secure communication scheme that uses the random fluctuation of the natural environment of communication channels. Only the transmitter and the receiver share the communication channel characteristics. From reciprocity between a transmitter and a receiver, it is possible for them to share one-time information of their fluctuating channel. This(More)
Analog approaches are expected to offer dramatically low power consumption in smart antennas, especially for battery-operated wireless terminal devices. This paper overviews recently developed analog antenna techniques for smart beamforming. Hardware architectures, trainedand blind-control criteria, and adaptation algorithms are introduced along with(More)
Principle, control theory, and application of the ESPAR (Electrically Steerable Parasitic Array Radiator) antenna are introduced. A typical ESPAR antenna consists of monopole or dipole elements, one of which is the radiator (fed element) and the others are the parasitic radiators with variable reactance devices loaded on them. It can provide a lower-cost(More)
In wireless sensor networks, reducing the energy consumption of the whole network is one of the most important research themes. In this paper, we first define a data aggregation model that defines the relationship between the increased amount of entropy and the number of sensor nodes. We also develop an intermittent transmission method, which is mainly(More)
A low-power consumption, small-size smart antenna, named electronically steerable parasitic array radiator (ESPAR), has been designed. Beamforming is achieved by tuning the load reactances at parasitic elements surrounding the active central element. A fast beamforming algorithm based on simultaneous perturbation stochastic approximation with a maximum(More)
This brief characterizes oneand two-port passive networks from the viewpoint of oscillator design. A linear circuit theory derives the spectral spread due to RF noise from active devices. The formulation finds a frequency derivative function of logarithmic immittance that plays the key role of dominating the spectrum behavior. This leads to an explicit(More)
The objective of the beamforming with the exploitation of a sensor array is to enhance the signals of the sources from desired directions, suppress the noises and the interfering signals from other directions, and/or simultaneously provide the localization of the associated sources. In this paper, we present a higher order cumulant-based beamforming(More)