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Graduate School of Science and Engineering
Electrical and Electronic Engineering

Communication Systems Laboratory

Wireless Communications Shaping the Dream of Future Society

Staff

Hideichi SASAOKA
[Professor]
MD
Telephone : +81-774-65-6355
sasaoka
Office : YE-415
Database of Researchers
Hisato IWAI
[Professor]
MD
Telephone : +81-774-65-6267
iwai
Office : YE-117
Database of Researchers

Research Topics

  • Encryption/security in wireless communications, coding technologies
  • Next generation mobile communications system/transmission technologies
  • Radio wave propagation, measurement technologies in wireless communications

Research Contents

In our laboratory we are researching technologies related to system configuration, wireless transmission, and radio wave propagation in various wireless communications systems. In particular, we aim to advance mobile communications by researching fundamental technologies such as wireless security, coding technologies, next generation mobile communications systems/technologies, radio wave propagation, and wireless measurement technologies. Our goal is to contribute to the realization of future multimedia mobile communications. Researches on these items are carried out by investigating new methods and technologies and evaluating their effectiveness with computer simulations and indoor/outdoor wireless experiments.

Our major research themes are the technologies in the fields of mobile communications and other wireless communications described below.

<1>
Wireless encryption/security, coding technologies in order to realize safer, even more reliable communications

<2>
Next generation mobile communications system/technologies in order to realize communications that are easy for users to use at even higher speeds and lower costs

<3>
Radio wave propagation, wireless measurement technologies in order to establish reliable and economic service areas and to eliminate/avoid interference from other cells and wireless communications
<1> Wireless encryption/security, coding technology
In wireless communications, all information is naturally transmitted with wireless channels in the air. Different from wired signal transmission where the transmission point and reception point are connected by a cable and the signal only propagates in a limited range, in wireless signal transmissions reception locations basically cannot be limited. There are security risks present in wireless signal transmission such as information eavesdropping, unauthorized usage of wireless networks, and falsification. Wireless LAN security, which has recently become a problem, is a typical example of this. For the problem, our laboratory is focusing on a method to share a private key between sending and receiving devices to prevent information interception/leakage by encryption. The principle of the method is based on the reversibility (reciprocity) and locality of wireless channels. By the method, a private key is shared between sending and receiving devices without transmitting key information over wireless channels. For this method, we run computer simulations that assume the propagation environment and qualitatively evaluate its performance.
In addition, we are also conducting research on error-correcting codes as a technology to improve transmission reliability of wireless communications. In particular, centered on a combination with adaptive modulation and adaptive coding technologies, we are working to research and develop new error-correcting codes suited to recent broadband wireless communications.

<2> Next generation mobile communications system/technology
In the mobile communications field, in continuation of the first generation (1G) analog automobile telephone system, the second generation (2G) early digital mobile communications system, and the third generation (3G) communications system advanced in high speeds and international standards, currently research and development of the so-called fourth generation (4G) of the mobile communications system is moving forward. In the fourth generation system, instead of a concept where a single large system comprehensively supports the entire environment and services, a concept where multiple systems are split up according to the usage environment or application, for example cellular communications to cover wide areas and wireless LANs suited to high-speed transmissions, is envisioned. The general idea is to call this collection of multiple systems "4G." A large increase in transmission capacity is also necessary with the personalization and ubiquity of wireless communications. The implementation of broadband transmissions is a fundamental technological challenge in 4G mobile communications. As is symbolized by the expression "anywhere, anytime, and with anyone," a major issue is also implementing technologies so as to provide easy-to-use and user-friendly communications at low prices.
For these problems, our laboratory is researching and developing next generation wireless transmission technologies, software-defined radio, and wireless ad hoc communications. Research on the next generation wireless transmission technologies is fundamental research about how to conduct broadband wireless transmissions within limited frequency resources. Specifically, OFDM, MC-CDMA, MIMO, CDMA, adaptive modulation, and other topics are our research subjects. For these methods we are formulating new technologies, qualitatively evaluating their performance by computer simulations and verifying their effectiveness.
Software-defined radio implements signal processing of radio equipment by software, until now done by hardware, the result is that wireless transmission methods can be changed by changing software. In order to implement the 4G system concept of splitting multiple systems according to usage environment and application, this is essential as a terminal-side technology. In particular, in order to constantly maintain an optimal system selection, simultaneous access to multiple (two or more) wireless systems with a single wireless circuit is deemed necessary, and we are working on research for the circuit configuration of software-defined radio terminals that implements this.
With the aim of also implementing future systems that are easy-to-use at low costs, we are advancing research on wireless ad hoc technology. Wireless ad hoc technology is a concept that attempts to implement information transmission by relaying it with terminals. For example, dead zones in cellular mobile communications systems can be eliminated by efficiently utilizing terminal relaying, and as a result, it makes the construction of economic wireless networks possible. In our laboratory we are specifically researching the wireless methods/multiplexing technologies suited to implementing wireless ad hoc.

<3> Radio wave propagation, measurement technology in wireless communications
When thinking about cellular telephone systems, for example, the installation location of base stations and as a result deciding how many base stations to install is a major issue in constructing cellular networks. In other words, there are problems such as dead zones where radio waves don't reach, making the supply of communications impossible, if the distance between base stations is too large, but on the other hand if base stations are densely installed, the dead zones are reduced but the cost of wireless network infrastructure construction increases. To resolve these issues, it is important to establish propagation models to precisely estimate propagation characteristics such as propagation losss, multipath delay characteristics and so on in a radio channel. In this way it is possible to design an optimal wireless network. In recent years, many forms of wireless communications have been developed such as wireless LAN local communications and UWB and RF-ID short distance communications. It is also important to construct propagation models for respective environments to establish these systems. In our laboratory we are researching these propagation models.
The research technique in our laboratory is mainly computer simulations, but eventually the evaluation and verification of wireless communications by wireless experiments using radio waves is necessary. For this we are also working on investigating and developing wireless experimentation techniques. For example, in an environment where interference exists, performance evaluations are conducted with actual radio waves emitted for the technologies developed in the laboratory, our private key sharing method for example, and along with research on those evaluation technologies, the effectiveness of the formulated technology is verified.

Keywords

  • Mobile communications
  • Modulation/Demodulation
  • Coding
  • Multipath fading
  • Coded modulation
  • Adaptive modulation
  • Adaptive equalization
  • Code Division Multiple Access (CDMA)
  • Orthogonal Frequency Division Multiplex (OFDM)
  • Wireless security

  • Private key
  • Wireless LAN
  • MIMO
  • MC-CDMA
  • Software-Defined Radio (SDR)
  • Mobile ad hoc
  • Radio wave propagation
  • Wireless measurement technology
  • Anti-interference technology

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