Tetsuya Miki

A Novel Wireless Positioning System for Seamless Internet Connectivity based on the WLAN Infrastructure

Nowadays, several positioning systems are available for outdoor localization, such as the global positioning system (GPS), assisted GPS (A-GPS), and other systems working on cellular networks, for example, time difference of arrival (TDOA), angle of arrival (AOA) and enhanced observed time difference of arrival (E-OTD). However, with the increasing use of mobile computing devices and an expansion of wireless local area networks (WLANs), there is a growing interest in indoor wireless positioning systems based on the WLAN infrastructure. Wireless positioning systems (WPS) based on this infrastructure can be used for indoor localization to determine the position of mobile users. In this paper, we present a novel wireless positioning system, based on the IEEE 802.11b standard, using a novel access point (AP) with two transceivers to improve the performance of WPS in terms of accuracy of the location estimation and to avoid service connectivity interruption. In our proposed system, the novel AP uses the second transceiver to find information from neighboring mobile stations (STAs) in the transmission range and then sends information in advance to associated APs, which estimate the location of the STA based on an internal database. We also use a TDOA technique to estimate the location of the STA when there is not enough information in the database (in this case, the STA moves into a new area where the system has not run the calibration phase). Using TDOA, the database can be generated and updated automatically. The initial results from our simulations show that the proposed system provides higher accuracy of location estimation than other related work and does not interrupt the Internet connection for end users in contrast with other proposed schemes.

Ultrawideband Wavelength Conversion Using Cascaded SOA-Based Wavelength Converters

An all-optical wavelength converter with a large wavelength hopping range is proposed and demonstrated. This converter consists of multistage cascaded wavelength converters using semiconductor optical amplifiers each with different gain band. Each of the cascaded wavelength converters enables us to perform both noninverted (NIV) and inverted (IV) operations. Conversion performance is compared at NIV and IV operations in terms of static characteristics as a function of input/output power of the converter. While good conversion performances are achieved at both operations, the IV wavelength conversion has better cascadability to obtain a high-quality converted signal for the cascaded scheme. Moreover, signal amplitude regeneration is demonstrated by repeating the IV wavelength conversion. Finally, we successfully demonstrate, for the first time, ultrawideband wavelength conversion, including over 300-nm wavelength hopping to the shorter wavelength side with a triple-stage cascaded wavelength converter

Multiwavelength erbium-doped fiber Fabry-Pe/spl acute/rot laser and its uniform spectral lines power operation

Multiwavelength erbium-doped fiber laser by means of phase modulation in a linear cavity configuration is presented. Stable multiwavelength lasing is achieved by applying any one of the waveforms of sine, square, sawtoothed, and triangular at a suitable frequency between 500 Hz to a few tens of kilohertz to the phase modulator. The output spectral lines power equalization is performed by adjusting the frequency to drive the all-fiber phase modulator and the polarization controller or dc offset voltage of a LiNbO/sub 3/ amplitude modulator, which is incorporated in a polarization-maintaining fiber Lyot-Sagnac filter.

A seamless handoff scheme with new AP module for wireless LANs support VoIP

Recently, wireless LANs based on the IEEE 802.11 standard have become popular and widely used, and voice over IP (VoIP) is one of the most promising to be used in mobile devices over wireless networks. Up to date, new technologies have improved providing high data rate to support various kind of real-time applications. However, besides the need for higher data rates, seamless handoff is another important issue to be addressed in order to continue supporting realtime services across wireless LANs. In this paper, we proposed a seamless handoff scheme that uses access point (AP) module with 2 transceivers in order to improve network efficiency in terms of supporting seamless handoff and balancing the traffic load in wireless network. In our proposed scheme, APs use the second transceiver to search for information of neighbor STAs in the transmission range, and later send the result back to associate AP, which in turn compare and analyze whether the STA should perform a handoff or not. The initial results from our simulations show the proposed handoff scheme is more effective than the conventional scheme in terms of low latency and traffic load is fairly balanced.

Photonic network R&D activities in Japan-current activities and future perspectives

R&D activities on photonic networks in Japan are presented. First, milestones in current ongoing R&D programs supported by Japanese government agencies are introduced, including long-distance and wavelength division multiplexing (WDM) fiber transmission, wavelength routing, optical burst switching (OBS), and control-plane technology for IP backbone networks. Their goal was set to evolve a legacy telecommunications network to IP-over-WDM networks by introducing technologies for WDM and wavelength routing. We then discuss the perspectives of so-called PHASE II R&D programs for photonic networks over the next 5 years until 2010, by focusing on the report that has been recently issued by the Photonic Internet Forum (PIF), a consortium that has major carriers, telecom vendors, and Japanese academics as members. The PHASE II R&D programs should serve to establish a photonic platform to provide abundant bandwidth on demand, at any time on a real-time basis, through the customers initiative to promote bandwidth-rich applications, such as grid computing, real-time digital-cinema streaming, medical and educational applications, and network storage in e-commerce.

All-optical wavelength conversion with large wavelength hopping by utilizing multistage cascaded SOA-based wavelength converters

A novel broadband wavelength converter by multistage cascaded semiconductor optical amplifier (SOA)-based wavelength converters is proposed. We have demonstrated, for the first time, broadband wavelength conversion in the wavelength range of 1320-1610 nm by using three-stage cascaded SOA-based wavelength converters with each different gain band.

Performances of a widely pulsewidth-tunable multiwavelength pulse generator by a single SOA-based delayed interferometric switch

Performances of a multiwavelength optical pulse generator by utilizing a single semiconductor optical amplifier (SOA)-based delayed interferometric switch are investigated. The generator enables us to generate multiwavelength clock pulse trains, which are synchronized with an optical clock. Moreover, the output waveform can be easily controlled by adjusting the time delay and phase offset of the interferometric switch. The obtained pulsewidth controllability is also useful to optimize the waveform according to transmission lines with different cumulative dispersions. We have verified that the pulsewidth tuning enables us to optimize transmission characteristics with various cumulative dispersion values, and have successfully obtained the improved transmission performances of the waveform-converted signals in comparison with conventional signals.

Broadband regenerative wavelength conversion and multicasting using triple-stage semiconductor-based wavelength converters

We demonstrate broadband wavelength conversion with a 320 nm operating wavelength range and channel spacing flexible wavelength-division-multiplexing (WDM) multicasting from a 1550 nm signal using a triple-stage cascaded semiconductor-optical-amplifier-based wavelength converter.

Widely pulsewidth-tunable multiwavelength synchronized pulse generation utilizing a single SOA-based delayed interferometric switch

We demonstrate a multiwavelength synchronized pulse generation, which utilizes a single semiconductor-optical-amplifier-based delayed interferometric switch. Simultaneous 16-channel pulse trains with wide pulsewidth tunability, up to the unity duty-ratio, have been successfully obtained at 10 Gb/s. The transmitter has a compact and functional configuration in comparison with supercontinuum light source.

Packet/cell loss recovery using variable FEC matrix for real time transport services over best effort networks

Real-time services over best-effort networks, such as teleconferencing over unspecified bit rate (UBR) class asynchronous transfer mode (ATM) networks or the Internet, are expected to be in high demand in the near future as such services become more cost effective. However, cell loss caused by buffer overflow at switches is a serious problem in this service class, and is responsible for degradation of the quality of service (QoS). A promising technology for improving the QoS of best-effort networks is the recovery of lost cells by forward error correction (FEC). Conventional FEC methods utilize a FEC matrix with fixed dimensions and which is usually designed to cope with the worst case of cell loss. In this paper, a new method that provides dynamic recovery capacity to deal with the current cell loss ratio through the use of a variable-dimension FEC matrix is proposed. The scheme also takes into account the coding method of the matrix to provide data prioritization. Numerical results show that the cell loss ratio and transmission efficiency of the proposed method are superior to those of conventional methods.