Kiyomichi Araki

Design and analysis of UWB band pass filter with ring filter

To realize an ultra wideband (UWB) bandpass filter (BPF) in wireless communications, a device is developed using a new ring filter. The ring filter is compact, with low insertion loss, sharp rejection and a constant group delay within the UWB pass band. The ring filter is made to control the attenuation pole frequency by adjusting both the ring and the stub impedance. A center frequency and a bandwidth of the 5-stage UWB BPF are designed based on the transmission line model. The circuit conditions of two attenuation poles at either side of the passband are given together with controlling them.

Practical data compression in wireless sensor networks: A survey

Power consumption is a critical problem affecting the lifetime of wireless sensor networks. A number of techniques have been proposed to solve this issue, such as energy-efficient medium access control or routing protocols. Among those proposed techniques, the data compression scheme is one that can be used to reduce transmitted data over wireless channels. This technique leads to a reduction in the required inter-node communication, which is the main power consumer in wireless sensor networks. In this article, a comprehensive review of existing data compression approaches in wireless sensor networks is provided. First, suitable sets of criteria are defined to classify existing techniques as well as to determine what practical data compression in wireless sensor networks should be. Next, the details of each classified compression category are described. Finally, their performance, open issues, limitations and suitable applications are analyzed and compared based on the criteria of practical data compression in wireless sensor networks.

Cooperative relaying scheme with space time code for multihop communications among single antenna terminals

In mobile multihop communications, the diversity technique is important since the channel between mobile terminals may suffer from the effects of fading and the routes between terminals are normally created through several hops. Space-time coding using multiple transmit antennas is an effective countermeasure for fading. For terminals which have only one antenna, due to the size/cost limitations, user cooperation has been introduced as a diversity technique. In this paper, a space-time coded cooperative relaying scheme for a multihop communications scenario, in cases where the number of hops is more than two, is proposed in order to combat the effects of fading among single antenna terminals, without bandwidth expansion. The scheme utilizes a space-time code for cooperative relaying and is developed in both frequency-flat and frequency-selective fading channels. By computer simulations, it is shown that the proposed scheme provides diversity gain and more improvement of frame error rate as the number of hops increases. Furthermore, the effects of an error correcting code and co-channel interference are shown.

MIMO Channel Capacity in an Indoor Line-Of-Sight (LOS) Environment

The effect of antenna correlation on the Multiple-Input Multiple-Output (MIMO) channel capacity in the real propagation environment is a topic of interest. In this paper, we present the results of a measurement campaign conducted in an indoor Line-Of-Sight (LOS) office environment. Channel responses were taken with varying distance in a static indoor environment. Results showed measurements with high received Signal-to-Noise Ratio (SNR) and a high level of correlation among the antenna elements. Further analysis of the results showed that MIMO systems can achieve sufficient channel capacity compared to the Single-Input Single-Output (SISO) system, despite high antenna correlation. Theoretical analysis reveals that when the SNR is sufficiently high, the loss in channel capacity due to high antenna correlation is relatively low. Therefore it is shown that in the indoor LOS environment, MIMO systems can be sufficiently efficient because the MIMO channel is more robust to antenna correlation when the SNR is high.

Overview of Elliptic Curve Cryptography

In this article, we look at the elliptic curve cryptography, which is believed to be one of the most promising candidates for the next generation cryptographic tool. The following issues are addressed here; 1. Discrete Logarithm Problem in finite fields 2. Elliptic Curve Discrete Logs 3. Implementation of ECDLP Cryptographic Schemes 4. Attacks on EC Cryptosystems 5. Minimum Requirement for Secure EC Cryptosystems 6. Standardization and Commercialization of EC Cryptosystems 7. Construction of Elliptic Curves

A robust and low complexity adaptive algorithm for mimo eigenmode transmission system with experimental validation

Adaptive MIMO eigenmode transmission system is a promising candidate for future high data rate wireless systems. However under practical conditions when channel state information (CSI) is imperfect, the eigenbeams lose their orthogonality and inter-eigenmode interference occurs. No work so far has attempted to consider the effects of inter-eigenmode interference on the adaptive signaling algorithm which is essential in ensuring a practical and robust adaptive system. Thus in this paper, we will propose an adaptive algorithm that account for CSI imperfections and practical operating conditions explicitly, namely imperfect channel estimation at receiver, delayed quantized feedback to transmitter and a spatially correlated continuous fading channel. A metric for the SINR of each eigenmode under the above practical conditions is identified and this metric is used in the adaptive signaling to ensure a robust adaptive algorithm. Both simulation and experimental results showed that the proposed algorithm is robust and superior to conventional schemes under practical operating conditions. Furthermore, a low complexity look up table-based computation method is also devised

On Generalized Feistel Structures Using the Diffusion Switching Mechanism

To design secure blockciphers, estimating immunity against differential attack and linear attack is essential. Recently, Diffusion Switching Mechanism (DSM) is proposed as a design framework to enhance the immunity of Feistel structure against differential attack and linear attack. In this paper, we give novel results on the effect of DSM on three generalized Feistel structures, i.e. Type-I, Type-II and Nybergs structures. We first show a method for roughly estimating lower bounds of a number of active S-boxes in Type-I and Type-II structures using DSM. Then we propose an improved search algorithm to find lower bounds for generalized structures efficiently. Experimental results obtained by the improved algorithm show that DSM raises lower bounds for all of the structures, and also show that Nybergs structure has the slowest diffusion effect among them when SP-type F-functions are used.

Experimental and analytical investigation of MIMO channel capacity in an indoor line-of-sight (LOS) environment

The paper present the results of a multiple-input multiple-output (MIMO) channel capacity measurement experiment conducted in an indoor line-of-sight (LOS) office environment. Channel responses were taken systematically with varying distance in a static indoor environment. Results showed measurements with high received signal-to-noise ratio (SNR) and a high level of correlation among the antenna elements. Further analysis of the results showed that MIMO systems can be efficient in the indoor LOS office environment, despite the high antenna correlation. Theoretical analysis reveals that when the SNR is sufficiently high, the loss in channel capacity due to high correlation is relatively low. Therefore, it is shown that in the indoor LOS environment, MIMO systems can be achieve sufficiently high channel capacity because the MIMO channel is more robust to correlation when the SNR is high.

A New Type of Isolator Using the Edge-Guided Mode (Letters)

Experirnents on a new edge-guided mode isolator are reported. In this isolator, one edge of a wide strip is shorted to the ground, and no lossy electrical materials are used. Large isolation and small insertion losses were obtained.

A group of modulation schemes for adaptive modulation

Adaptive modulation increases the throughput of a wireless network by adjusting the modulation scheme to the channel status. To have more capacity and more flexibility in using adaptive modulation, our research attempts to find a group of modulation schemes, which includes M-QAM where the number of signal points is not a power of 2, as well as non-squared QAM (or APSK: amplitude and phase-shift keying), so we can have n-bit modulation where n ranges fully from 1 to 6 including half-integer indices. Some recent research has shown that the gap between QPSK and 16-QAM, 16-QAM and 32-QAM, 32-QAM and 64-QAM can be filled smoothly by introducing 12-QAM, 24-QAM and 48-QAM. But the gap between QPSK (4-QAM) and 12-QAM is still an open problem. In this paper we insert 8-ary modulation schemes, and propose 6-ary modulation schemes. Simulation results show that our proposed group can fill smoothly the gap between QPSK and 12-QAM.