In this paper, the quality and transferred data based video bitrate control method for web-conferencing services is proposed, aiming to reduce transferred data by suppressing excessive quality. In web-conferencing services, the video bitrate is generally controlled in accordance with the network conditions (e.g., jitter and packet loss rate) to improve users' quality. However, in such a control, the bitrate is excessively high when the network conditions is sufficiently high (e.g., high throughput and low jitter), which causes an increased transferred data volume. The increased volume of data transferred leads to increased operational costs, such as network costs for service providers. To solve this problem, we developed a method to control the video bitrate of each user to achieve the required quality determined by the service provider. This method is implemented in an actual web-conferencing system and evaluated under various conditions. It was shown that the bitrate could be controlled in accordance with the required quality to reduce the transferred data volume.

We have proposed a mortar-shaped structure to improve response time and alignment uniformity of twisted vertically aligned (TVA) mode liquid crystal displays (LCDs) for high-contrast reflective color LCDs. From the results of the simulation, we clarified that response time, alignment uniformity and viewing angle range of TVA-mode LCDs were improved by controlling the liquid crystal alignment axis-symmetrically in each pixel.

Nonvolatile flip-flop enables leakage power reduction in logic circuits and quick return from standby mode. However, it has limited write endurance, and its power consumption for writing is larger than that of conventional D flip-flop (DFF). For this reason, it is important to reduce the number of write operations. The write operations can be reduced by stopping the clock signal to synchronous flip-flops because write operations are executed only when the clock is applied to the flip-flops. In such clock gating, a method using Exclusive OR (XOR) of the current value and the new value as the control signal is well known. The XOR based method is effective, but there are several cases where the write operations can be reduced even if the current value and the new value are different. The paper proposes a method to detect such unnecessary write operations based on state transition analysis, and proposes a write control method to save power consumption of nonvolatile flip-flops. In the method, redundant bits are detected to reduce the number of write operations. If the next state and the outputs do not depend on some current bit, the bit is redundant and not necessary to write. The method is based on Binary Decision Diagram (BDD) calculation. We construct write control circuits to stop the clock signal by converting BDDs representing a set of states where write operations are unnecessary. Proposed method can be combined with the XOR based method and reduce the total write operations. We apply combined method to some benchmark circuits and estimate the power consumption with Synopsys NanoSim. On average, 15.0% power consumption can be reduced compared with only the XOR based method.

We present a new power supply control method, which achieves constant flow Rate control for the thrust of a 20 mN-class Hall thruster. First, we present observations of a 20 mN-class Hall thruster with oscillation-mode-map. We make a theoretical study of the thrust and experiments on electrical characteristics of the Hall thruster, and conclude that thrust, thrust efficiency and low frequency oscillation are clearly determined by the external control parameters, anode voltage, gas flow rate, and magnetic flux density. Second, we discuss how to control the power supplies to suppress the power consumption, especially when the operation or thruster conditions change temporarily during use. The new method will be a very important guideline for Hall thruster system design and operation, in particular making it easy to manage the power consumption in a satellite by controlling the thrust resources. As a result of performance experiments for a 20 mN-class Hall thruster, over 36% thrust efficiency of the Hall thruster was found to be sensitive to the anode voltage and applied magnetic flux density. The new power control method achieves constant flow rate control method of the thrust. The benefits are light weight and low cost.

Satellite Internet is one of the most important networks for emergency communications because of its tolerant of disasters such as earthquake. Therefore, satellite Internet has received considerable attention over recent years. However, most standard implementations of TCP congestion control method perform poorly in satellite Internet due to its high bit error rate and long propagation delay. This paper proposes a new TCP congestion control method called TCP-STAR to improve the throughput over satellite Internet. TCP-STAR has three new mechanisms, namely Congestion Window Setting (CWS) based on available bandwidth, Lift Window Control (LWC), and Acknowledgment Error Notification (AEN). CWS can resist the reduction of the transmission rate when data losses are caused by bit error. LWC is able to increase the congestion window quickly based on the estimated available bandwidth. AEN can avoid the reduction of the throughput by mis-retransmission of data. The mis-retransmission is caused by ack losses or delay. Simulations show that TCP-STAR can obtain the best throughput comparing with other TCP variants (TCP-J and TCP-WestwoodBR). Furthermore, we found that the fairness of TCP-STAR is a little lower than that of TCP-WestwoodBR. However, the fairness of TCP-STAR is equal to TCP-J.

One effective way to make a large-capacity mobile communication system is to use a microcellular system. One way to do this is to place the base station antennas lower than the surrounding buildings. This result in what is called a street microcellular system. We previously presented basic simulation results evaluating the performance of a different-sized cell combination algorithm (DCC) designed to avoid the problems due to an unbalanced distribution of traffic in street microcellular systems. In this paper, we present the results of simulations evaluating the performance of an improved active different-sized cell combination method (ADCC) that controls the transmission power of each base station.

In the current ATM AAL5 implementation, even a single cell loss event can lead to the corruption of one whole packet. Hence, it has been observed that the throughput of upper layer protocol may easily collapse on a congested ATM network. In this paper, we propose a buffer management method called Age Priority Packet Discarding (APPD) scheme to be used along with two other schemes: the Early Packet Discarding (EPD) and the Partial Packet Discarding (PPD) schemes. After describing the operations and the pseudo code of the proposed APPD scheme and how it operates with the EPD/PPD schemes, the packet level QoS of APPD and its extended versions are derived analytically under homogeneous ON-OFF source model. Numerical results obtained via analytical approach suggest that the proposed APPD scheme can more effectively and fairly reduce packet loss probability than other schemes.

This paper proposes a request-grant-type multiple access control called bandwidth-request labeled-slot multiple access (BLMA) for wireless LANs. BLMA employs slotted ALOHA in the request stage and has an algorithm to avoid unfair access due to the capture effect in this stage. In BLMA, terminals transmit data using fixed length slots called fragment slots in the transmission stage. The base station assigns the fragment slots one by one to terminals for peer-to-peer communication in which terminals communicate directly. It also controls the retransmission based on the stop and wait automatic repeat request scheme. The base station retransmits data for the source terminal as much as it can. BLMA provides simple and fair access control, efficient link utilization, and easy implementation. It also allows modes to be easily changed automatically from peer-to-peer communication to store-and-forward communication in which terminals communicate via the base station. Design concepts of a wireless MAC discussed and details of BLMA are described. The evaluation results of the BLMA are also shown.

This paper describes configuration and operation of a high-frequency link resonant inverter using cycloconverter techniques. In this inverter, a resonant link high-frequency voltage generated in a primary resonant inverter is isolated by a high-frequency transformer, then directly converted into a resonant link low-frequency voltage in a cycloconverter. The switching losses and surge voltage levels can be reduced by making all switches in the primary inverter and the cycloconverter operate at zero voltage. The relationship between characteristic impedance of the resonant circuit and the conversion efficiency, and the distortion factor characteristics of the output voltage waveforms are discussed by comparing of analytical and experimental results.

This paper describes a new configuration and control method for an uninterruptible power supply (UPS) with a bidirectional cycloconverter. When commercial AC power is operating normally, the load is supplied by commercial AC power and the bidirectional cycloconverter operates as a battery charger. During interruptions of commercial AC power, the bidirectional cycloconverter operates as an inverter and supplies AC power to the load. Unlike a conventional UPS, this new configuration does not require a battery charger, so it can be small, light-weight, cost-effective, and highly efficient. The output voltage characteristics and the transient voltage drop in the output when commercial AC power fails are also discussed by numerical analysis and experiments.