We used simulations and experiments to investigate the filtering penalty caused by optical filters such as wavelength-selective switches for a 128-Gbit/s PDM-QPSK signal transmission system based on digital coherent detection technology. In particular, to take account of the center frequency shift of optical filters in practical transmission lines, we define an approach for evaluating the optical filtering penalty. Moreover, we explain that the optical filtering penalty in a digital coherent detection system has characteristics that are distinctly different from those of conventional transmission systems based on direct detection technology when we compare the simulation results for a 43-Gbit/s DQPSK signal transmission system as an example.

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This paper proposes an access control protocol method for multicast transmission to reduce packet loss caused by collisions and/or interferences in WLAN (wireless local area network) systems. Multicast transmission may achieve effective bandwidth use because packets are delivered to more than one mobile station simultaneously in single transmissions. However, because multicast transmission does not have a retransmission function, the communication quality deteriorates by packet collision and interference waves from other systems. The proposed method avoids both these issues. It is validated by a simulation showing multicast packet loss reduction of about 20% and a higher multicast throughput improvement compared to conventional methods, in an environment with traffic congestion and interference waves.

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Parametric wavelength converters are capable of simultaneously converting multiple wavelength pairs in contrast to traditional tunable converters. We therefore attempt to reduce the total number of converters required in a network by employing parametric converters network-wide under a first-fit wavelength assignment. Unfortunately, contrary to general intuition, our analyses indicate that parametric converters achieve no significant reduction with a sequential wavelength indexing based first-fit assignment, since it leads to a misalignment of wavelength conversion pairs at individual nodes. This letter proposes a median flip-flop indexing scheme that remedies this issue and significantly improves converter utilization. Numerical results indicate up to 57% reduction in total converters required.

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This paper proposes a ZigBee-based system and scheme to obtain location and vital health information. ZigBee systems are wireless communication systems defined by IEEE 802.15.4. Location information is obtained using a Link Quality Indication (LQI) function of the ZigBee system, which means the received signal strength. Vital health information is received as ZigBee sensor data when the terminal stations are moving. The proposed scheme facilitates the management of action history and health conditions for medical patients. Experiments using an actual ZigBee system confirm that the proposed scheme provides accurate location and vital health information using sensor data.

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In this paper, switch induced in-band crosstalk impairment is used for evaluating the number of monitoring devices with respect to the amount of reported monitoring information in items of optical signal to crosstalk ratio. Partial Set Cover model and greedy algorithm with four heuristic parameters are proposed for placing the monitor devices for performance evaluation. The numerical results showed that heuristic parameters, Interference Rate (IR) and Highest Crosstalk Analytical Value which are computed during network operation, outperform parameters, highest degree and lowest degree which are determined at network planning stage in NSF, GRID and Mesh topologies.

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A low-profile antenna with an array of dogbone-shaped elements is presented. The proposed structure is a surface wave antenna on which a 2-by-2 dogbone array is installed. As a result, main beams directed to the reverse each other are parallel to the longest part of the dogbone elements, and shows a narrow beam width. The radiation pattern has been changed from the omni-directional pattern of a conventional surface wave antenna with a 2-by-2 square patch array.

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