In the development of intrabody communication systems, it is important to understand the effects of user's posture on the communication channels. In this study, dynamic measurements of intrabody communication channels were made and their dependences on the grounding conditions were investigated. Furthermore, the physical mechanism of the dynamic communication channels was discussed based on electrostatic simulations. According to the measured and the simulated results, the variations in the signal transmission characteristics depend not only on the distance between the Tx and the Rx but also on the shadowing by body parts.

Wide area virtualization of wireless transceivers by centrally managed software radio systems is a way to efficiently share the resources for supporting a variety of wireless protocols. In order to enable wide-area virtualization of wireless transceivers, the authors have developed a mechanism to deliver the radio space information which is quantized broadband radio wave information including the radio signals to the transceivers. Delivery mechanism consists of a distribution server which distributes radio space corresponding to the request of the client such as the center frequency and the bandwidth and a client which uses the radio space information. Accumulation of the distribution servers which deliver radio space information simultaneously to a large number of clients will contribute to build an infrastructure for any clients ubiquitously distributed over the globe. In this paper, scale-out architecture of a distribution server is proposed to deliver unlimitedly broadband radio space information to unlimited number of clients. Experimental implementation indicates the architecture to be a scale-out solution, while the number of clients is restricted by the computer resources of the distribution server. The band pass filter processing for individual client in the distribution server consumes the dominant part of the processing power, and the number of CPU cores is the upper limit of clients supportable for the distribution server in the current operating system implementation. The logical increase of the number of CPU cores by hardware multithreading does not contribute to relax this limit. We also discuss the guidance architecture or building server derived from these conclusions.

A direct-conversion receiver integrated with the CMOS subharmonic frequency tripler (SFT) for V-band applications is designed, fabricated and measured using 0.13-µm CMOS technology. The receiver consists of a low-noise amplifier, a down-conversion mixer, an output buffer, and an SFT. A fully differential SFT is introduced to relax the requirements on the design of the frequency synthesizer. Thus, the operational frequency of the frequency synthesizer in the proposed receiver is only 20 GHz. The fabricated receiver has a maximum conversion gain of 19.4 dB, a minimum single-side band noise figure of 10.2 dB, the input-referred 1-dB compression point of -20 dBm and the input third order inter-modulation intercept point of -8.3 dB. It draws only 15.8 mA from a 1.2-V power supply with a total chip area of 0.794 mm0.794 mm. As a result, it is feasible to apply the proposed receiver in low-power wireless transceiver in the V-band applications.

Over the past ten years, the demand for low-cost, low-power, and small form-factor portable wireless devices has led to the integration of RF transceivers on the same silicon as digital processors to form wireless systems-on-a-chip. This paper describes the challenges in designing CMOS systems-on-a-chip for wireless communications. RF transceiver building blocks for signal amplification, frequency translation, and frequency selectivity are examined with special emphasis on low noise amplifiers, power amplifiers, mixers, and frequency synthesizers. System-on-a-chip integration issues such as leakage currents of digital logic, calibration techniques, and noise coupling are also discussed.

The characteristics of various techniques, including some new techniques, in mitigating wavelength contention in optical path setups were compared by simulations. The assumed network here is a WDM photonic network in which each node is equipped with a limited number of wavelength-tunable optical transceivers. In the photonic network, the frequency of optical path setups and releases is very high, because optical path lifetime is short and optical transceivers are time-shared, and therefore, the wavelength contention becomes a serious problem. In this paper, we propose four new techniques to mitigate the phenomenon. In those techniques, a new small-sized parameter, the history number, was introduced based on the conceptual requirements of the assumed network, namely, low-cost and low additional control load. The four proposed techniques are history recording (HR), history notifying (HN), conditional random selection (CRS), and HN with dithering target (HNDT). We have evaluated the characteristics of those techniques along with those of two conventional techniques: no mitigation and random selection (RS). The simulations were carried out while varying four parameters: the maximum generation number, the optical path lifetime, the number of wavelengths, and the number of optical transceivers per node. Consequently, it is clarified that for a sufficient number of wavelengths, namely, almost no limitation on number of wavelengths, the CRS technique is advantageous, and for a small number of wavelengths the HNDT technique is advantageous.

An on-package dual-mode square-loop band pass filter is studied by applying a non-uniform finite difference time domain (NU-FDTD) method. The filter is integrated on a package containing a transceiver, and it is designed to operate in dual-modes, i.e., and , to ensure a good electric performance around the center frequency at 5.25 GHz, which is commonly allocated in wireless local area network (WLAN). This filter is also referred as a dual-mode integrated-circuit package filter (DM-ICPF) based on its operational mode and integration onto an IC-package. The frequency characteristics in terms of the scattering parameters are studied, and the results are validated against the computed results using commercial software, the high frequency structure simulator (HFSS). Results show an excellent agreement between the numerical data, and the proposed DM-ICPF structure can be applied in the area of the highly integrated wireless transceivers.

The discovery of the Turbo codes has driven research on the creation of new signal detection concepts that are, in general, referred to as the Turbo approach. Recently, this approach has made a drastic change in creating signal detection techniques and algorithms such as equalization of inter-symbol interference (ISI) experienced by broadband single carrier signaling over mobile radio channels. A goal of this paper is to provide readers with broad views and knowledge of the Turbo concept-based Multiple-Input Multiple-Output (MIMO) signal transmission techniques. How the techniques have been developed in various applications and how they perform in real-field environments are introduced.

This paper considers the design of quadrature amplitude modulation (QAM) transceivers for fixed wireless communications. We propose the use of power control in the QAM transmitter (Tx) to obtain BER performance robust to fading. The gain of the Tx is adaptively adjusted to keep the power of the received signal nearly constant despite of the short term fading and the second multipath. The BER performance of the proposed scheme is analytically evaluated in fixed wireless channels with flat fading and frequency selective fading. Analytic and simulation results show that the use of power control in the Tx can provide the BER performance only about 1 dB inferior to that in additive white Gaussian noise (AWGN) channel.