Academia Program

Information and Communication Network Laboratory at Niigata University researches communication systems and applications of wireless ad-hoc networks. This presentation reports our activities on IETF, a research project of vehicular ad hoc networks, and experimental projects of ad hoc network systems “Yamakoshi-net” and “Skymesh” for large-scale disaster recovery.

In order to construct the highly sophisticated ubiquitous society, some key technologies on the field of communication, health-care and positioning are studied at Kohno laboratory in Yokohama National University. In addition to some conventional researches that are designed for reliable efficient systems, significant studies which cover multiple research fields are also undertaken. In this presentation, some of our researches that include important technologies such as UWB (Ultra Wideband) radio, Cognitive Radio, medical-ICT (Information and Communication Technology) are introduced. As the novel UWB based technology, impulse-transmitting system and originally designed coding system which can achieve high date-rate and high efficiency are introduced. Besides them, some other UWB techniques such as ranging and positioning which can be applied for ITS (Intelligent Transport System) are also proposed. In this age of rapid progress of wireless communication technology, interference over multiple systems is serious problem. As cognitive Radio technology, some novel techniques for coexistence and interference reduction are introduced. Especially, the coexistence issue between newly coming wireless system and other conventional systems are focused on. Finally, the medical techniques that support future aging society are discussed. As the novel research filed, the medical ICT which combines between conventional medical techniques and information techniques are introduced, and some interesting studies such as body-area network or hyperthermia are proposed.

Emerging wireless technologies, such as IEEE 802.11 wireless local area networks, beyond third generation (B3G) cellular networks and mobile WiMAX, provide high-speed Internet access for wireless users. Using these high-speed wireless access, wireless users can use peer-to-peer (P2P) content-sharing services and share their content with other wireless users and with fixed users. In P2P content sharing, users can share their content by contributing their own resources to one another. However, since there is no incentive for contributing contents or resources to others, users may attempt to obtain content without any contribution. To motivate users to contribute their resources to the service, incentive-rewarding mechanisms have been proposed. However, this diversification of access networks makes it difficult to appropriately assign rewards to each user according to their contributions. This is because the cost necessary for contribution is different in different access networks. In this presentation, we propose a novel incentive-rewarding mechanism called EMOTIVER that can assign rewards to users appropriately. Considering the diversity of cost incurred by users, we also investigate a way of appropriately controlling rewards.

Development of microwave and millimeterwave dielectric materials has been expected on the wireless communications in the ubiquitous communication society. There are three important directions for research and development of microwave and millimeterwave dielectric materials. We have been studied on these three directions based on the crystallography. At the first direction for miniaturization of mobile equipments, tungstenbronze-type like Ba6-3xR8+2xTi18O54 ( R = rare earth ) solid solutions with high dielectric constant have been studied to be improved quality factor based on the compositional ordering of cations. At the second direction for base station of mobile phone, homologous ALa4Ti4O15 (A=Ba, Sr and Ca) compounds have excellent dielectric properties of high dielectric constant and high quality factor. At the third direction for millimeterwave dielectric, silicate compounds such as forsterite Mg2SiO4 and willemite Zn2SiO4 are expected for millimeterwave dielectrics which quality factor are improved using high purity law materials, and alumina Al2O3 was also improved using special law materials. Temperature coefficients of resonant frequency tf of these materials are improved adding rutile with high plus tf.

Wireless Systems Laboratory was founded at Kanda Campus of Tokyo Denki University in 2001. Its research activities include:  Ultra wideband wireless systems: UWB antennas and propagation; development of UWB signal sources and high-sensitivity detectors; experimental and numerical evaluation of interference between UWB and incumbent narrowband wireless systems; development of UWB electromagnetic human phantoms; UWB microwave mammography; UWB short range vehicular radar; and development of a UWB system simultaneously undertaking ranging and communications. The first UWB experimental radio station license was granted by the government in 2003 among universities and research institutes in Japan.  Teletraffic characterization of mobile communication networks: characterization of mobility of mobile of terminal platforms (pedestrians, vehicles, and trains) based on measurements; and evaluation of teletraffic characteristics (statistics of channel occupancy time at base stations, handoff rates, handoff failure rates, and so forth) of cellular communication networks.  Urban radio propagation for mobile and personal communications: characterization and modeling of time-varying occultation of propagation paths by pedestrians and vehicles.  Lessons from failures and mistakes in the process of development and deployment of various wireless systems. The outlines of these activities and some transferable technologies will be presented.

One way to get high data rates and bandwidth efficiency is the combination of multiple-input multiple-output (MIMO) signal processing with orthogonal frequency division multiplexing (OFDM). In MIMO-OFDM systems, increased capacity is achievable when channel state information (CSI) is known at both the transmitter and receiver. However, CSI at the transmitter becomes outdated due to the processing and the feedback delay. Therefore, the channel estimation performance is degraded, so channel prediction is required to mitigate this phenomenon. Wiener filter has been discussed about channel prediction with MIMO. However, Wiener filter has strong constrained conditions of assuming stationarity and infinite time observation. In this paper, we use Kalman filter removing those assumption and propose a method of channel prediction based on high-order autoregressive (AR) model. Simulation results show that the scheme offers more accurate CSI and gives good prediction performance.

With the proliferation of tiny sensing device with the capability of wireless communication, wireless sensor network technologies have been attracting much interest from academia and industry for their wide range of applications in these days. Since the number of sensor nodes ranges from tens to thousands, the quality of wireless communication dynamically changes, communication pattern changes application by application and time by time, and topology also changes for addition, movement, and removal of nodes, conventional centralized controls are not useful anymore and a need for new self-organizing control mechanisms and protocols accomplished by autonomous and local behavior of nodes emerges. In this presentation, we introduce some of our work on self-organizing sensor network technologies. Our self-organizing control mechanisms are scalable to the number of nodes and the size of monitored region, adaptive to changes in communication patterns and communication environment, and robust to node failures and program errors, by basing on knowledge on non-linear controls in the field of mathematics, physics, and biology.

Wearable Equipment is a promising technology as the novel human interface for mobile communications. However, it is not yet widely used by consumers because of its performance and appearance. In this paper, new wearable equipment was manufactured and applied for a human navigation system. Tiny LEDs are attached on the rim of the eye glasses and indicate the direction and distance to a user. Portable PC, GPS receiver and terrestrial magnetism sensor are used with the wearable eye glasses. The eye glasses and other equipment are connected by wireless transceiver for the convenience of the user. Field experiments verified the navigation function of the proposed wearable equipment.

This paper proposes an indoor event detection scheme using an electric wave for home or office security. The proposed system exploits an antenna array on the receiver side, and only a pair of transmitter and receiver are used in the environment of interest. To detect an event, we use eigenvector spanning signal subspace obtained by space-time signal processing of antenna array. The eigenvector is not based on received signal strengths (RSS) but on the direction of arrival (DOA) of incident signals on an antenna array. Therefore, the performance degradation of event diction owing to noise and fading is low. In addition, though multiple elements are needed at the receiver, this system is simple because narrowband signals can be used, and the proposed method can be used together with other wireless services, such as WLAN. In this paper, we show the experimental results in home and office. The experimental results reveal that the proposed method can detect events.

By the digital revolution that began in the 1990's following the Industrial Revolution, the mankind have come to be able to enjoy richness. However, on the other hand, causing global warming is beginning to erode earth environment. Ecology is born into the consciousness of people, however to the life style of mankind usage of ICT is an indispensable thing now. Under such a situation, in order that mankind secure earth environment, on the basis of the view point that utilizes effective and efficient ICT, We will make a presentation on the role of ICT for coexistence as Green ICT.

By taking into account ubiquitous networks and multi dimensional mobile communication networks, research subjects are determined as follows. (1) In order to develop very small antennas for RFID tags, 0.035 wavelength normal mode helical antenna is developed. By comparing communication distances of this antenna tag and the conventional tag, high efficiencies of this antenna are ensured. (2) In TPMS (Tire Pressure Measurement System), electromagnetic simulations of a car are made for a transmitter contained in a tire. (3) For terrestrial digital TV applications, very wideband antenna of W-loop configuration is developed. Wideband performances and radiation characteristics of car mounted situations are made clear through electromagnetic simulations. (4)For the collision avoidance radar of the intelligent transportation system (ITS), a shaped dielectric lens antenna is developed. (5)Accurate measurement and calculation methods of the radar cross section (RCS) are also studying.

Directional MAC protocols in many of studies so far use a beam pattern of directional antennas so as to get the highest gain in the desired angle. However, only maximizing a main robe, we never utilize variety in beam forming functionality of the adaptive array antenna to the full. Nonetheless, there are no study has reported until now which covers all the beam pattern of many-element ESPAR antenna. Therefore we investigate the possibility of forming independent lobes in two known different azimuth angles in seven-element ESPAR antenna. And then we show an application to a directional MAC protocol by exploiting this beam forming. We use seven-element ESPAR antenna which is adaptable to environmental change and suitable on terminals. The directivity of the ESPAR antenna is controllable by reactance values of a varactor connected to each parasitic element. However, since the relation between reactance of varactor and directivity is non-linear, it is difficult to calculate the reactance values for forming a desired directivity pattern with analytic formulation. Therefore we used a random search method in this study and we evaluated the directivity given by obtained reactance values from the MAC viewpoint. Simulation results show that the ESPAR antenna can form a desired twin-lobe beam pattern if the difference in azimuth angle between two desired directions are 90 degrees or wider.

For ubiquitous society, there is a great demand for reliable and high data rate broadband mobile communication systems. For its realization, OFDM(Orthogonal Frequency Division Multiplexing) is one of the most promising technologies for next generation mobile communications, and it has high spectrum efficiency. However, an OFDM signal consists of a number of independently modulated subcarriers, which can give a large peak-to-power ratio(PAPR). One of the peak reduction methods, CI-OFDM is proposed, but it can’t reduce PAPR significantly. In this paper, as a solution to reduce the PAPR, we propose oversampling spectrum spreading roll-off OFDM(OSSR-OFDM). In OSSR-OFDM, by spreading on frequency domain after serial-to-parallel conversion, each carriers form an impulse response of raised-cosine filter and they are orthogonal each other in time domain. The result of computer simulation show that our proposal show about 5dB PAPR reduction at with almost the same spectrum and no degradation of BER. We also propose its low-complexity architecture.

As a mature technique, orthogonal frequency division multiplexing (OFDM) has been adopted in various wireless communication standards, such as DVB, IEEE 802.11, and wireless USB.　Using the overlapped subcarriers, OFDM has high spectral efficiency, however at a price of sensitivity to carrier frequency offset .　 On the other hand, the recent demand of low-cost terminals leads to the use of direct-conversion transceiver (DCT). By removing the expensive intermediate frequency part, DCT has remarkable merits in circuit-board size, cost, and power consumption. However, DCT also introduces additional analog impairments, for example, I/Q imbalance. The I/Q imbalance arises from the non-ideal local oscillators (LOs) and branch components in the transmitter and receiver. According to the frequency characteristics, I/Q imbalance can be categorized into two types. The LO imbalance, namely, imperfect phase difference and unequal amplitudes, is constant over signal bandwidth thus frequency-independent. The imbalance induced by branch components with mismatched frequency responses is naturally frequency-dependent. These analog impairments associated with the DCT result in severe performance degradation of OFDM systems. We are working on the digital processing techniques for the compensation of these RF/analog impairments in the OFDM-DCT. In particular, we focus on the low-complexity solution for practical implementation. Our results include international journal and conference papers, as well as several filed patents.

In recent years, MIMO technology has become an important to wireless communication systems because it makes high-speed, high-quality data communication possible in various types of channels. Given this factor, we have already proposed a 4x2 MIMO-OFDM system which completes maximum data rates 600Mbps and propagated distance 40-meter on TGn channel B. In this report, we report a RTL design and verification of this system’s PHY layer using a FPGA prototyping board and propose a MAC protocol using channel reserving and continuous transmission.

An introduction to an MEXT-Supported research aimed at a mobile phone-based Electrocardiography. The basic concept, the main results, and possible applications are described.

Komaki Lab., Osaka Univ. and Matsumoto Lab., Waseda Univ. are doing a collaborative Research Project on Radio on Free Space Optics (RoFSO) Communication System in order to realize a quick and cost-effective delivery of heterogeneous wireless services to areas where have no optical fiber infrastructures and face difficulties to construct broadband fiber networks. The proposed system aims at achieving effective fusion of optical fiber and a wireless system. Various types of wireless services are transparently transported in an optical free space channel. At Komaki Lab, Osaka Univ., are developing RoFSO equipments with seamless connection of optical fiber and free-space and RoF-RoFSO Interface equipments, evaluating their performances, and performing the system design. At Matsumoto Lab., Waseda Univ., some experimental examinations are being performed to derive parameters for the evaluation of atmospheric propagation characteristics of optical signal conveying RF signals, and also a new universal link margin design with a refractive-index air structure constant (Cn2) is investigated. In this presentation, some results of our collaborative development will be briefly introduced.