Hiroki Harada

Soil-inhabiting tardigrade communities in forests of Central Japan

This study was carried out for the purpose of detecting the relationship between soil-inhabiting tardigrade communities and environmental factors of various forests. Nine forests in the southern part of Kanagawa Prefecture, Central Japan, were selected for this study. Four vegetation types were designated; broadleaved (evergreen/deciduous), coniferous and orchard. In these sites, dry weight of leaf litter, soil pH, soil hardness, soil moisture content and porosity ratio were measured. Wet soil faunal frequencies were also described. The Baermann funnel method was adopted for collecting tardigrades, and DIC microscopy was used for specific identification. To clarify the correlation between environmental variables and tardigrade faunae, multivariate analysis was applied. The tardigrade fauna occurred as two distinct groups. The first group primarily contained Macrobiotus species. The second group contained the genus Diphascon (e.g. D. nobilei, D. patanei, D. prorsirostre). An exception to this was D. pingue, included in the former. Most of the Diphascon species were concentrated in Nebu (coniferous forest site), while, Macrobiotus species were dominant in other sites. Distinct environmental factors could not be identified, but the nematodal frequency was recognized as the main factor in forming these groups. The uniqueness of Nebu, which does not correspond to large-scaled vegetational classification, was substantiated by statistical data. Nebu’s coniferous forest apparently has created a unique environment for sustaining rare species (Diphascon species). This study concluded that forests should be evaluated not only by the macroscopic factors, such as landscape, but also by the microscopic communities, such as those including the tardigrades.

Channel Modeling and Signaling of Medical Implanted Communication Systems and a Step to Medical ICT

Recently, the use of wireless communications devices in the field of medical implants has received great deal of concern due to miniaturization of electronic circuits. By means of transmitting vital data such as blood pressure, blood glucose level and pulse, we can observe the body condition and detect any possible problems in the human body at anytime and anywhere. These devices can help doctors to diagnose and cure diseases. For wireless communications, in the case of inside or between inside and outside of the human body, channel propagation considerably differs more than in freespace. So, it is necessary to construct a new channel model of the human body. In this paper, we analyze wideband channel characteristics in the body based on the measurements and the theory of electromagnetic wave propagation. Based on the measured data, we propose a new frequency domain channel model in the body by using Zero-Pole parameters. We show that the generated channel and the measured channel have similar statical properties by analyzing autocorrelation function of frequency response, power delay profile and cumulative distribution function of power.

Channel Estimation for Wavelet Packet based UWB Transmissions

Maximum likelihood (ML) data aided channel estimation for wavelet packets based ultra wideband (WP-UWB) transmissions is investigated. Training pilot symbols are employed for ML channel estimation based on a least square algorithm derived from the optimum ML approach. An optimum training sequences criterion is derived. Based on this, nearly optimum perfect root of unity sequences (PRUS) are tested and compared to Gold sequences and random sequences. In this estimation strategy, a generalized inverse of the training pilot symbols matrix can be pre-computed and stored in memory. Furthermore, PRUS allows to save the inverse matrix operation and so reducing the complexity of the ML estimator significantly. This technique is especially attractive for low data rate transmissions as in sensor networks because of its low complex implementation. Performance analysis results in terms of the MSE are provided. Tradeoffs between performance and complexity are described as well. The investigated channel estimation algorithms for UWB channels offer flexibility, low complexity and robustness, making channel estimation fairly simple and effective

Multiuser Channel Estimation in Wavelet Packet-UWB Systems

Centralized maximum likelihood (ML) data aided channel estimation for wavelet packets based ultra wideband (WP-UWB) transmissions is investigated. Training pilot symbols are employed for joint ML channel estimation based on a least square algorithm derived from the optimum ML approach. An optimum training sequence criterion is derived. Based on this, nearly optimum perfect root of unity sequences (PRUS) are tested and compared to Gold sequences and random sequences. In this estimation strategy, a generalized inverse of the training pilot symbols matrix can be pre-computed and stored in memory. Furthermore, PRUS allows to save the inverse matrix operation and so reducing the complexity of the joint ML estimator significantly. This technique is especially attractive for low data rate transmissions as in sensor networks because of its low complex implementation. Performance analysis results in terms of the MSE and BER for a single user matched filter are provided. Trade-offs between performance and complexity are described as well. The investigated channel estimation algorithms for UWB channels offer flexibility, low complexity and robustness, making channel estimation fairly simple and effective.

Multiband and multicarrier wavelet packet multiplexing for UWB transmissions

We propose a novel multi-channel modulation scheme for UWB transmissions based on the discrete wavelet packet transform (DWPT) and DWT combined with spread spectrum and multiband approaches (as analogous to multicarrier CDMA and multiband OFDM). Thus, two possible structures are proposed for UWB transmissions. Namely, multiband DWT multiplexing and DWT-CDMA multiplexing. Indeed, the proposed techniques divide UWB channels into a set of parallel channels. Exploiting the properties of wavelets in time and frequency, a set of multi-channel basis functions can be formed such that the corresponding channel-output functions remain nearly orthogonal for any UWB channel. Multiple access can be introduced in the form of time-frequency hopping codes (similar to multiband OFDM) or by introducing spreading codes (similar to multicarrier CDMA). The proposals are compared to multiband OFDM and multicarrier CDMA in terms of BER performance.

Multi-channel UWB system design based on wavelet packets

We propose a novel multi-channel modulation scheme for UWB transmissions based on wavelet packets waveforms. The propose technique divides either the entire UWB channel or a part of it (similar to multi-band OFDM). Exploiting the properties of wavelet packets (WPs) in time and frequency, a set of multi-channel basis functions can be formed such that the corresponding channel-output functions remain nearly orthogonal for any UWB channel. The signal design satisfies the generalized Nyquist criterion, so that ML detection can be implemented by matched filtering with each basis function.