Effects of imprint on signal margin in FeRAM with Pt/SrBi2Ta2O9/Pt capacitors have been investigated. Imprint, induced during high temperature storage, significantly reduced the signal margin and hence determines lifetime of FeRAM. Initial signal margin of 470 mV is reduced to 290 mV after storage at 175C for 96 hours. From the reduction rate of the signal margin, it is estimated that imprint lifetime of the FeRAM is more than 10 years even though the storage temperature is 175C.

A 1T2C-type ferroelectric memory cell, in which two ferroelectric capacitors with the same area are connected to the gate of an usual MOSFET with a SiO2/Si interface, was fabricated and characterized. The relations between various device parameters and characteristics of memory cell were investigated by using SPICE simulation. It was found from the simulation results that the memory window significantly changed by the device parameters, which means that the operation voltage of the memory cell can be well controlled by these parameters. The fabricated cell is composed of a stacked gate structure of Pt/SBT/Pt/Ti/SiO2/Si with the area ratio of the MOS capacitor (SO) to the ferroelectric capacitor (SF) of 6 or 10. Nonvolatile memory operation was confirmed, and the obtained memory window coincided with the simulated results qualitatively. Furthermore, the current on/off ratio in the read-out operation was larger than 3-order-of magnitude and the data retention time was longer than 6 104 seconds. It was also predicted that low voltage operation was possible if the device parameters were optimized.

We describe a simplified receiver structure having several receiving antennas (i.e., an adaptive array antenna system) and using time-division-multiplexing (TDM) signal processing. Three simplified receiver structures were investigated for use in the antenna system. To confirm the feasibility of using a TDM receiver, both a TDM receiver and a conventional adaptive array receiver were constructed for testing. In our proposed system, several repetitions of the constant modulus algorithm (CMA) are used to reduce co-channel interference (CCI). The frame format used for both receivers was the same as that of the personal handy phone system in Japan. The laboratory testing was done using a fading simulator to enable measurement of the bit error rate. The results are very promising and show the feasibility of the TDM receiver.

The stage 3/2 decoding scheme, originally suggested by U. Timor, is modified for a Rayleigh fading channel to improve the performance of a fast frequency-hopped multiple access/multilevel frequency shift keying system. When signal-to-noise ratio per bit is 30 dB, the simulation results show that the modified stage 3/2 decoding scheme increases the spectral efficiency by 11% compared to the modified stage 1 decoding scheme at bit error rate of 10-3. Further, the performance comparisons are made between the modified multistage decoding scheme and the diversity combining methods, where the modified stage 3/2 decoding scheme shows better performance.

The inter-cell interference between uplinks and downlinks in CDMA packet communication systems, employing a shared-TDD scheme, is evaluated under cellular environments. It is found that interference between base stations rarely degrades uplink throughput, but interference between mobile stations substantially degrades downlink throughput. A transmission power control scheme is proposed to improve the downlink throughput. The proposed scheme increases the transmission power of downlink packets when they are re-transmitted, and thus, improves the signal-to-interference ratio of the downlink re-transmission packets. Computer simulation shows that this scheme increases downlink throughput without sacrificing the uplink throughput until the uplink throughput reaches a maximum value.

Sequence estimation (SE) of narrow-band digital FM signals, such as CPFSK and GMSK, with non-coherent limiter/discriminator (L/D) and integrate and dump (I&D) detection is investigated in detail using both analysis and simulation. The BER is studied from approximate upper and lower bounds obtained through Chernoff bounding techniques and minimum error event path probability along with a Gaussian noise assumption for high SNR. Various IF filters and the dependence of the error probability upon modulation index are considered. The results show an optimum modulation index around h 0.55, and clearly demonstrate the effectiveness and limitations of sequence estimation.

This paper proposes a λ-ring system that is a wavelength-based self-healing-ring application unlike ordinary fiber-based ones. To design survivable networks of interconnected such self-healing ring systems, a virtual mesh network scheme is used, in which wavelength assignment in virtual links can be considered according to the λ-ring-system or fiber-ring-system applications of the bidirectional wavelength-path switched architecture. Integer-programming-based design problems are then formulated that minimize the total fiber length in these self-healing-ring applications. Numerical examples show that the λ-ring-system application is always superior to 4-fiber and 2-fiber-ring-system applications and 1+1 end-to-end path protection.

In server load balancing where replicated servers are dispersed geographically and accesses from clients are distributed to replicated servers, a way of distributing the accesses from clients to an adequate server plays an important role from the viewpoint of load balancing. In the paper, we propose a new network paradigm for server load balancing using active anycast. In active anycast, an end user only sends its request to group of servers using an anycast address. When this request arrives at an active router, it selects an adequate server from the viewpoint of load balancing and changes the anycast address of a packet to the unicast address of the selected server. The decision which server is the best one from the viewpoint of server load balancing is made by an active router rather than an end user, so active anycast is a network-initiated method. Simulation results show that active anycast can accomplish efficient server load balancing, even when a small part of routers are equipped with active network technology.

We have developed a new scheme to provide Diffserv-based QoS over ATM access networks. Well-known Diffserv over ATM scheme requires some extension for conventional routers with ATM interfaces. The routers must map their Diffserv classes of services into ATM QoS classes and forward IP packets into prioritized VCs based on DSCP (DiffServ Code Point). The purpose of this work is to provide Diffserv-based QoS over ATM network using conventional IP over ATM interfaces on routers. We propose DSCP snooping at ATM edge nodes, which differentiates services over a single VC between two IP domains. A prototype circuit was used to evaluate this scheme.

The differentiated services (diffserv) architecture has been proposed for implementing scalable service differentiation in the Internet. Expedited forwarding and assured forwarding have been standardized as Per-Hop Behaviors (PHB) in diffserv. Assured forwarding can be utilized to realize the service, which provides each user with a minimum guaranteed rate and a fair share of the residual bandwidth. We call it guaranteed rate (GR) service. With GR service, each packet for flow i is marked in or out based on comparison between the sending rate and the minimum guaranteed rate. When congestion occurs in networks, out packets are dropped more aggressively than in packets. Recently, several fair queuing schemes have been proposed for core stateless networks. They can achieve fairer bandwidth allocation than random early detection (RED). However, there have not been any studies that consider in/out bit usage to support GR service. This paper proposes how to extend the schemes that have been proposed for core stateless networks to allow the support of in/out bit usage. We present the performance of one of the extended schemes and compare the scheme to RED with in/out bit (RIO) in terms of fair bandwidth allocation.

In this paper, we survey the fairness issues in the congestion control mechanisms of TCP, which is one of most important service aspects in the current and future Internet. We first summarize the problems from a perspective of the fair service among connections. Several solution methods are next surveyed. Those are modifications of TCP congestion control mechanism and router support for achieving the fair service among TCP connections. We finally investigate the fair share of resources at endhosts.

The chemical stability of the constituent elements in polycrystalline Sr-Bi-Ta-O thin film with various Bi content prepared by metalorganic chemical vapor deposition (MOCVD) was investigated by X-ray photoelectron spectroscopy (XPS). Moreover, that of the epitaxial films was also investigated to estimate the effect of the grain boundary in polycrystalline films. Therefore, only the Bi element drastically changed from Bi3+ state to Bi0 one by the Ar sputtering. This change increased with increasing the Ta/Bi mole ratio in the film from 0.64 to 1.67. This result was observed not only for the polycrystalline films but also for the epitaxial films, suggesting that this is the grain character not grain boundary one. The stability and the leakage character of the film strongly depend on the constituent of the film.

A 2-step deposition technique was introduced in the heteroepitaxial growth of barium titanate (BaTiO3) thin films. Heteroepitaxial BaTiO3 films were prepared on a SrRuO3/SrTiO3 substrate by radio frequency (RF) magnetron sputtering with three kinds of deposition method: low RF-power deposition, 2-step deposition, and high power deposition. The crystallographic and ferroelectric properties were evaluated for the heteroepitaxial films. When the epitaxial capacitor was prepared by the 2-step deposition technique, the ferroelectric remanent polarization, 2Pr, was maximized. The optimized deposition condition to improve the crystal quality is discussed in terms of damage and diffusion, which could be introduced into the oxide films during the epitaxial growth, and controlled by the RF-power and deposition time, respectively.

Epitaxial SrTiO3(STO) film on epitaxial (Ti,Al)N/Si(100) was successfully obtained using a Ti-buffer layer. The SrTiO3 film was (100) oriented and grew in parallel epitaxial relationship (cube-on-cube), i.e., (100)SrTiO3//(100)(Ti,Al)N//(100)Si, <110> SrTiO3//<110> (Ti,Al)N//<110> Si. The Ti-buffer layer was grown on (Ti,Al)N by magnetron sputtering, and the thickness of the buffer layer was 2-10 nm. After the STO film was sputtered, the Ti-buffer layer was changed to polycrystalline anatase-TiO2.

We demonstrate all-optical clock recovery at 160 Gbit/s by injection locking of a 10 GHz mode-locked laser diode. Effective locking in a range of 10 MHz is observed for average input powers around -10 dBm. The timing jitter is analyzed for data rates between 10 Gbit/s and 160 Gbit/s. Beyond 40 Gbit/s, the high frequency timing jitter of the slave laser becomes of prime importance and has to be taken into account since it degrades the performance of a subsequent receiver. Increasing power penalties are found, especially beyond 80 Gbit/s.

In a mobile computing environment, the characteristics of wireless communication and host mobility are important considerations in providing an efficient payment service. Currently, most payment systems were not intended for use in a mobile environment, and as such they inherently possess some inefficient properties. In this paper, we propose a new micropayment system (AMPS), designed for use in a mobile computing environment. AMPS reduces the computational load of mobile hosts by directing operations normally performed by the client to the static portion of the network. With AMPS, a client's request for goods goes to a TTP server, called the AMPS server, using only one message. The client can also be disconnected while the AMPS server deals with the merchant, reducing communication costs and power consumption. User privacy is protected by hiding the details of the payment to the AMPS server. The AMPS server can also provide client anonymity to merchants. Another advantage of AMPS is the provision of transaction atomicity by checking goods and money before forwarding to clients or merchants, and preserving all necessary information for any possible future disputes.

In distributed network systems, it is one of the most important problems how to assign the files to servers in view of cost and delay. It is obvious that there is a trading-off relationship between costs and delays in these systems. In order to evaluate the optimization that the total cost is minimized subject to the total delay, we have presented the Optimal File Allocation Model as 0-1 integer programming, and have investigated the general characteristics in distributed systems. In this model, we have introduced many cost and delay parameters to evaluate the total cost and delay in the system more exactly. In constructing practical systems, it is necessary to investigate the weight and the contribution of each parameter to the total cost. It is very useful to show how to estimate cost and delay parameters on the basis of this analysis. In this paper, we analyze the sensitivity of these parameters and make clear the influence between principal parameters.

One drawback of Integrated service architecture is the scaling problem. Therefore, flow aggregation is an important solution for supporting quality of service in large-scale network. In advance reservation, priori information of advance-reserved requests can be used for flow aggregation before their initiation time. However, an impolitic aggregation can lead to violate admission control. In this paper, we propose an effective algorithm to aggregate advance-reserved requests with guaranteed delay. The proposed algorithm not only can reduce the amount of state in core network but also minimize the bandwidth consumption. The simulation result indicates that the state in the core network can be reduced as low as 17.3% even in the worst case.

Various shadows are one of main factors that cause errors in vision based vehicle detection. In this paper, two simple methods, land mark based method and BS & Edge method, are proposed for vehicle detection and shadow rejection. In the experiments, the accuracy of vehicle detection is higher than 98%, during which the shadows arisen from roadside buildings grew considerably. Based on these two methods, vehicle counting, tracking, classification, and speed estimation are achieved so that real-time traffic parameters concerning traffic flow can be extracted to describe the load of each lane.

In this paper, we first propose a new speech enhancement preprocessing algorithm by combining power subtraction method and maximal ratio combining technique, then apply it to both energy-based and statistical model-based VAD algorithm to improve the performance even in low SNR conditions. We also perform extensive computer simulations to demonstrate the performance improvement of the proposed VAD algorithm employing the proposed speech enhancement preprocessing algorithm under various background noise environments.