Network Systems

Digital TV on mobile receivers

In Japan, high definition television (HDTV) is provided using digital terrestrial television (DTTV) broadcasting. In addition to HDTV, a narrow band digital television service dedicated to handheld terminals, known as "One-Seg TV", is popular now. After the termination of analog TV services, multimedia broadcasting services have started using the vacated VHF analog TV band. However, it is difficult to improve reception reliability in mobile and handheld environments. This laboratory is working on developing low power-consumption and reliable handheld digital TV receivers using array antennas and radio signal processing techniques.

Mobile communication systems

With recent research and development activities, the bit rate of mobile communication systems, such as cellular systems and wireless local area networks (W-LAN), is increasing rapidly. However, its reliability is not satisfactory for error intolerant purposes, such as surveillance, networked robots, etc. In order to solve this problem, our laboratory studies key technologies including OFDM (Orthogonal Frequency Division Multiplex), MIMO (Multiple Input Multiple Output), diversity, and multihop mesh networks. We are working on implementing these technologies into specific systems such as W-LAN, WiMAX, and Zig-Bee.

Radio on fiber and distributed antenna systems

We are studying the Radio on Fiber (RoF) technique in order to construct a heterogeneous backhaul infrastructure for various types of broadband wireless signals such as LTE, WiMAX, mobile multimedia contents broadcasting, etc. In this regard, we also investigate sophisticated signal processing capabilities of distributed antenna system (DAS) in multi-user, MIMO scenarios for achieving further performance enhancement.

Wireless sensor networks

Although radio wave-based sensor systems, such as RADAR and GPS, are capable of measuring positions over a wide area, their function is limited. To enhance their applicability, we propose various kinds of sensing networks using radio waves, for example, rain rate estimation using millimeter-wave mesh links, intruder sensing in leaky coaxial cable infrastructure, and positioning sensors for medical applications using RFID tags.

Wireless power transfer

There has been an increasing demand for wireless power transfer (WPT) for mobile nodes. Although many WPT systems have been developed and are widely used, it is difficult to transfer power to moving nodes using WPT. In conventional WPT using electromagnetic coupling, the distance between the transmitter and receiver is limited to few tens of centimeters. The motion of the power reception nodes leads to a decrease in the power transfer efficiency due to impedance mismatching.
Network Systems Laboratory is now working on developing a wide-area WPT system using a parallel feeder line. This system is capable of accommodating mobile receiving nodes including vehicles.