We propose a novel visible light communication system for rail-guided industrial vehicles using orthogonal frequency-division multiplexing (OFDM) modulation. This system implements two types of optical fibers as downlink/uplink communication lines. The purpose of this system is to realize fast real-time communication with hand-over functionality, introducing carrier modulation. A downlink distance of 100 m and uplink distance of 30 m were achieved at the primary modulation of 16QAM 1/2. In our previously reported system, only single-channel communication could be performed. However, the system demonstrated in this study can be effectively applied to fast mobile communication with multiple channels by introducing OFDM modulation. Moreover, hand-over functionality can be easily realized by this system.

White LEDs were invented the 1990's. Since then they have been extensively researched and applied in various ways. Compared with conventional lighting devices, the white LED has lower power consumption, lower voltage requirements, longer lifetime, smaller size, faster response, and cooler operation. The white LED will eventually replace incandescent or fluorescent lights in offices and homes. We have proposed an indoor visible light wireless communication system that utilizes multiple white LED lighting equipment. In this system, the equipment is used not only for illuminating rooms but also for an optical wireless communication system. The system has significantly higher power levels than infrared wireless communication systems, since it also functions as the main lighting equipment. One problem is we tend to install many lighting sources on a ceiling in order to illuminate the room as evenly as possible. While the number of sources permits site diversity transmission over LOS links, the optical path difference between the multiple sources triggers intersymbol interference (ISI), which significantly degrades system performance. This paper overcomes the ISI problem by proposing an adaptive equalization system. We elucidate the most effective training sequence interval for channel estimation in a mobile environment. And we show that the adaptive equalization system with the effectual interval alleviates the influence of shadowing.

We propose a new receiving method for visible light communication with LED-based traffic lights using 2-dimentional image sensor receiver. First, we discuss the maximum receiver's field of view (FOV) when using the 2-dimentional image sensor and we analyzed the best vertical inclination for the proposed system. We used 2-Pulse Position Modulation (PPM) and Select Best (SB) Combining Technique. We analyzed and quantified the improvement in term of the enhancement of received signal-noise ratio (SNR) when different numbers of pixels were applied. Our results indicate that using more pixels increases the received SNR and the service area becomes wider compared to the conventional system using Avalanche Photodiode (APD) receiver. We found that the optimum number of pixels to accomplish a reliable communication system is 50 × 50. Receivable information within the service area also increases and we show that proposed system is more suitable for the Intelligent Transport Communication (ITS).

In order to obtain an appropriate, high level of security, a number of architectural elements for secure downloading of software to a software defined radio (SDR) terminal have been pointed out. They include four different cryptographic techniques and employment of tamper resistant hardware. The cryptographic techniques employed are: (a) a secret key encryption technique; (b) a public key encryption technique; (c) a technique for cryptographic hashing and (d) a technique for digital signature. Particularly, a protocol for exchanging cryptographic components in an automatic manner without any assistance from the user, is proposed. Implementation characteristics of certain cryptographic components are also discussed.

Future electric lights will be composed of white LED (light emitting diodes). Indoor wireless optical communication systems utilizing white LED lights have been proposed in our laboratory and we have been studying it. Generally, plural lights are installed in our room. Therefore, their optical path difference must be considered. In this paper, the influence of optical path difference has been investigated and two approaches for this problem are introduced. One uses OOK-RZ (on-off keying, return-to-zero) coding and the other uses optical OFDM (orthogonal frequency division multiplexing). From the results of computer simulations, we have found that these approaches are feasible for wireless optical communication systems utilizing white LED lights.

A new software defined radio platform with multiport-based direct conversion is proposed, named SOPRANO (Software Programmable and Hardware Reconfigurable Architecture for Network). The main features of SOPRANO are a high-level design methodology for digital circuits, a new mixer-less direct conversion method, and software algorithms for multi-band and multi-mode operation. We built the first prototype SOPRANO 1.0, which was able to receive PSK and QAM signals with two different carrier frequencies at 2.45 GHz and 5.25 GHz by changing signal processing software.

This paper investigates the optimal access point placement in a simultaneous broadcast system using orthogonal frequency division multiplexing (OFDM) for high data rate indoor wireless LAN. We aim to determine the best combination of multiple AP placements that minimizes the average bit error rate (BER) of terminals when input information including an indoor configuration, a number of APs, and total transmission power is given a priori. Since this AP placement problem is categorized as a hard combinatorial problem with many variables and constraints, we applied a nonlinear optimization scheme called very fast simulated annealing to search for an approximate optimal solution. The simulation results demonstrate that the algorithm has been successfully applied to the AP placement problem and its effectiveness was also confirmed in comparison with a local search algorithm.

We propose a wireless optical communication system with white colored LEDs for a wireless home link (WHL). The white colored LEDs have a high power output and are regarded as lamps for the next generation. In the proposed system, this device is used for a wireless home link. The proposed system is suitable for private networks such as consumer communication networks. From numerical and simulation results, it is confirmed that the proposed system is available and the problems to be solved are made clear.

A VLSI two-layer channel router designed to find solutions which minimize both wiring area and number of vias simultaneously is presented. The method, called topological channel routing, analyzes the topological relationship of wires before the wires are mapped onto the channel. A unique layout design rule called an interleaving mesh is used. The interleaving mesh prohibits long wires on one layer from overlapping with wires on the other layer, and thus has smaller crosstalk of signals because of smaller capacitive couplings between those wires on different layers. Experimental results show that the algorithm generates very good solutions. For example, a height of 41 for Deutsch's Difficult Example without any parallel overlaps of wires has been obtained and simultaneously, with a via count of 186, which is one of the best results ever reported in the literature.>

A novel method is proposed for the two-layer topological channel routing problem. The authors' algorithm takes geometric information into consideration when a topological solution is obtained. Experimental results show that the algorithm generates very good solutions. For example, the authors have obtained a height of 41 for Deutsch's difficult example without any parallel overlaps of wires while simultaneously achieving a via count of 219.>

An approach to two-layer channel routing using a layout model which utilizes the channel area more efficiently than the traditional layout model is presented. The model allows horizontal and vertical wire segments to be placed on both layers while avoiding the crosstalk problem. In order to have as many nets without vias as possible, the crossing relationship among the nets is determined before they are mapped onto a channel. Preliminary experimental results are very encouraging.>