This paper presents an evolutionary technique to build and maintain fault-recoverable digital circuits. As the synthesis of a circuit by genetic algorithm is progressed according to the circuit behavioral objectives and interactions with the environments, the knowledge regarding the architecture as well as the placement and routing processes is not the major concern of the proposed method. The evolutionary behavior of the circuit also prevents the circuit from stuck-at faults by continuously modifying the neighboring circuit blocks accordingly. This is done without the prior knowledge of where and how the faults occur because of the evolutionary nature. Thus, the overhead circuit blocks for fault diagnosis and redundancy are minimized with this design. The fault-recoverable evolvable hardware circuits are synthesized to build a few combinational logics by evolution and the fault recovery capabilities are shown with the reconfigurable FPGA.

We investigated the dependence of the desired echo return loss on frequency for various hands-free telecommunication conditions by subjective assessment. The desired echo return loss as a function of frequency (DERLf) is an important factor in the design and performance evaluation of a subband echo canceller, and it is a measure of what is considered an acceptable echo caused by electrical loss in the transmission line. The DERLf during single-talk was obtained as attenuated band-limited echo levels that subjects did not find objectionable when listening to the near-end speech and its band-limited echo under various hands-free telecommunication conditions. When we investigated the DERLf during double-talk, subjects also heard the speech in the far-end room from a loudspeaker. The echo was limited to a 250-Hz bandwidth assuming the use of a subband echo canceller. The test results showed that: (1) when the transmission delay was short (30 ms), the echo component around 2 to 3 kHz was the most objectionable to listeners; (2) as the transmission delay rose to 300 ms, the echo component around 1 kHz became the most objectionable; (3) when the room reverberation time was relatively long (about 500 ms), the echo component around 1 kHz was the most objectionable, even if the transmission delay was short; and (4) the DERLf during double-talk was about 5 to 10 dB lower than that during single-talk. Use of these DERLf values will enable the design of more efficient subband echo cancellers.

To enhance fault tolerance ability of the feedforward neural networks (NNs for short) implemented in hardware, we discuss the learning algorithm that converges without adding extra neurons and a large amount of extra learning time and cycles. Our algorithm modified from the standard backpropagation algorithm (SBPA for short) limits synaptic weights of neurons in range during learning phase. The upper and lower bounds of the weights are calculated according to the average and standard deviation of them. Then our algorithm reupdates any weight beyond the calculated range to the upper or lower bound. Since the above enables us to decrease the standard deviation of the weights, it is useful in enhancing fault tolerance. We apply NNs trained with other algorithms and our one to a character recognition problem. It is shown that our one is superior to other ones in reliability, extra learning time and/or extra learning cycles. Besides we clarify that our algorithm never degrades the generalization ability of NNs although it coerces the weights within the calculated range.

We propose a new interference cancellation technique using reference signals for optical synchronous code-division multiple-access (CDMA) systems. In the proposed system, we use the signature code sequences composed of the group information codes and the modified prime code sequences. The group information codes are added in the forefront of the signature code sequences to estimate the amount of the multiple access interference (MAI). The proposed cancellation scheme can be realized with the simpler structure than the conventional canceller using the time division reference signal, because it can reduce the number of optical correlators from P to two where P is the prime number. We analyze the performance of the proposed system with considering the effects of the MAI, avalanche photodiode (APD) noise, and thermal noise. We show that the proposed canceller has better bit error probability than the conventional canceller.

This paper proposes a fault tolerant optical crossconnect (FTOXC) which can tolerate link, channel, and internal optical switch failures via spare optical channels, extra input/output (I/O) ports for an optical switch, and associated wavelength converters. It also proposes a fault tolerant wavelength routing algorithm (FTWRA) which is used in the normal and the restored state. The FTOXC and FTWRA can be applied to any all-optical network and can recover many types of failures. FTOXC can configure the number of working and spare channels in each output link based on the traffic demand. Two formulations in this paper can be used to determine the optimal settings of channels. A global optimal setting of working and spare channels in each link can be found by formulating the problem as an integer linear program (ILP). In addition, the number of working and spare channels in each link can be dynamically adjusted according to the traffic loads and the system reliability requirements. The tradeoff between these two conflicting objectives is analyzed by the Markov decision process (MDP).

We investigate possibility of fault-tolerant and self-stabilizing protocols (ftss protocols) using an unreliable failure detector. Our main contribution is (1) to newly introduce k-accuracy of an unreliable failure detector, (2) to show that k-accuracy of a failure detector is necessary for any ftss k-group consensus protocol, and (3) to present three ftss k-group consensus protocols using a k-accurate and weakly complete failure detector under the read/write daemon on complete networks and on (n-k+1)-connected networks, and under the central daemon on complete networks.

A Rayleigh lidar (laser radar) system was developed and is now working well for temperature observations of the middle atmosphere at Poker Flat Research Range near Fairbanks, Alaska (65.1 N, 147.5 W). A comparison of lidar data and balloon sonde data showed good agreement in overlapped altitudes. The atmospheric fluctuations are detected in the temperature profiles obtained by the Rayleigh lidar and these are useful for the study of gravity waves. A Rayleigh Doppler lidar for wind measurements of the middle atmosphere is under the phase of development. The expected accuracy in measurements of horizontal winds up to an altitude of 60 km is smaller than 6 m/s in 2 hours observation. The system will be operated at Poker Flat after the completion of development. The combination of these lidars and radars installed at Poker Flat, give us chances of simultaneous observations of the structure and dynamics of the atmosphere in broad range of altitudes. Here, we give descriptions of the Rayleigh lidar and the Rayleigh Doppler lidar for the observations of the Arctic middle atmosphere at Poker Flat.

The purpose of this letter is to modify the correlation least mean squares algorithm using a sum of the lagged squared errors as the cost function and extend the modified CLMS algorithm to two-dimensional domain. The effectiveness of the proposed algorithm is shown by the computer simulation.

Meteor storms and showers are now considered as potential hazard in the space environment. Radar observations of meteors has an advantage of a much higher sensitivity over optical observations. The MU radar of Kyoto University, Japan has a unique capability of very fast beam steerability as well as a high sensitivity to the echoes from ionization around the meteors. We developed a special observation scheme which enables us to determine the orbit of individual meteors. The direction of the target is determined by comparing the echo intensity at three adjacent beams. The Doppler pulse compression technique is applied to improve the signal-to-noise ratio of the echoes from the very fast target, and also to determine the range accurately. The developed scheme was applied to the observation made during the Leonid meteor storm on November 18, 1998 (JST). Estimated orbital distribution seems to suggest that the very weak meteors detected by the MU radar are dominated by sporadic meteors rather than the stream meteors associated with the Leonids storm.

We gave in [1] the software and hardware algorithms for reconfiguring 1 1/2-track switch 2-D mesh arrays with faults of processing elements, avoiding them. This paper shows an implementation of the hardware algorithm using an FPGA device, and by the logical simulation confirms the correctness of the behavior and evaluates reconfiguration time. From the result it is found that a self-repairable system is realizable and the system is useful for the run-time as well as fabrication-time reconfiguration because it requires no host computer to execute the reconfiguration algorithm and the reconfiguration time is very short.

This work presents two novel algorithms to prevent rollback propagation for independent checkpointing: an efficient adaptive independent checkpointing algorithm and an optimized adaptive independent checkpointing algorithm. The last opportunity strategy that yields a better performance than the conservation strategy is also employed to prevent useless checkpoints for both causal rewinding paths and non-causal rewinding paths. The two methods proposed herein are domino effect-free and require only a limited amount of control information. They also take less unnecessary adaptive checkpoints than other algorithms. Furthermore, experimental results indicate that the checkpoint overhead of our techniques is lower than that of the coordinated checkpointing and domino effect-free algorithms for service-providing applications.

Non-real-time (NRT) services such as nrt-VBR, ABR and UBR traffic are intended for data applications. Although NRT services do not have stringent QoS requirements for cell transfer delay and cell delay variation, ATM networks should provide NRT services while considering other criteria to ensure an excellent performance such as cell loss ratio (CLR), buffer size requirement and service fairness. Service fairness means that networks should treat all connections fairly. That is, connections with low arrival rates should not be discriminated against. In addition, given a fixed buffer size for a connection, reducing the maximum number of cells in a buffer during the lifetime of a connection can lead to a low CLR due to buffer overflow. Thus, these criteria should be considered as much as possible when designing a cell scheduler to provide NRT services. Whereas most of the conventional cell scheduling schemes are usually appropriate for one performance criterion, but inappropriate for another one. In this work, we present a novel cell scheduling scheme, called buffer minimized and service fairness (BMSF), to schedule NRT services in ATM networks. Using probability constraints and selecting a connection with the longest buffer size to transmit first allow BMSF to attain a satisfactory performance with respect to maximum buffer size requirement, CLR, and service fairness in terms of the maximum buffer size and cell waiting delay criteria. Simulation results demonstrate that BMSF performs better than some conventional schemes in terms of these criteria, particularly when NRT services have diverse arrival rates. Thus, the BMSF scheme proposed herein can feasibly schedule NRT services in ATM networks.

To provide a bounded-delay service with an end-to-end delay guarantee and utilize network efficiently, the admission control functions in a network require an adequate per-switch delay allocation policy to allocate end-to-end delay requirement to a set of local switches. This letter present an optimal delay allocation policy, according to a deterministic traffic model, and a rate-controlled scheduler. Empirical results indicate that the proposed policy perform better than EQ allocation policy, using the admission load region as index.

We have developed spectral separation devices for processing femtosecond pulses. These devices are based on an optical coupler structure with fiber gratings. In a computer simulation, we confirmed that these devices could extract <1 nm bandwidth light with 80% efficiency. We fabricated the spectral separation devices using single mode fibers and highly Ge-doped fibers. These devices successfully extracted narrow spectral light of 0.3 nm bandwidth with 37% efficiency from femtosecond pulses of 40 nm bandwidth. We also fabricated 2-channel spectral separation devices, which could extract the light from each grating channel.

For FA (factory automation) and ATE (automatic test equipment) in the industrial area, the standard bus is required to increase the system performance of multiprocessor environment. VME (versa module european package format) bus is appropriated to the standard bus but has the features that is the small of package and the low density of board. Beside, the density of board and semiconductor have grown to become a significant issues that affect the development time, project cost and field diagnostics. To fit this trend, in this paper, the author composed Revision C. 1 (IEEE Std. P1014-1987) of the integrated environment for the main function such as arbitration, interrupt and interface between VMEbus and several control modules. Also the designed VME system controller is implemented on FPGA that can be located even into Slot 1. The control and function modules are coded with VHDL mid-fixed description method and then those operations are verified by simulation. As a result of experiment, the author confirmed that the most important about the operation of Bus timer that Bus error signal should occur within 56 µs, and both control and function modules have the reciprocal operation correctly. Thus, the constructed VHDL library will be able to apply the system based VMEbus and ASIC design.

This paper describes a transaction model for open environments based on mobile agents. Mobile agent-based transactions combine mobility and the execution of control flows with transactional semantics. The model presented represents an approach for providing reliability and correctness of the execution of distributed activities, which fulfills important requirements of applications in Open Environments. The presented transaction model is based on a protocol for providing fault tolerance when executing mobile agent-based activities. This protocol is outlined in this paper. With this protocol, if an agent executing an activity at an agency (logical "place" in a distributed agent environment) becomes unreachable for a long time, the execution of the activity can be recovered and continue at another agency. The fault tolerance approach supports "multi-agent activities," i. e. , activities where some of its parts are spawned to execute and migrate asynchronously in relation to other parts. The described transaction model, called the basic (agent-based) transaction model, is an open nested transaction model. By being based on the presented fault tolerance mechanism, subtransactions can be executed asynchronously in relation to their parent transactions and agent-based transactions can explore alternatives in the event of agent unavailability. The model fulfills requirements for supporting the autonomy of organizations in a distributed agent environment.

A novel K-band MMIC frequency doubler has been developed using resistive series feedback circuit. The doubler exhibits much better D/U ratio, smaller output power variation against ambient temperature and lower power consumption than those of the conventional single-ended doubler. This paper presents the simulation results on the effect of the resistive series feedback by harmonic balance methods. To obtain practical and accurate simulation results, newly developed gate charge model for Cgs and Cgd is introduced. The fabricated result of the proposed MMIC is also demonstrated.

This letter presents a subspace-based technique with generalized sidelobe canceler structure, which can be utilized to deal with the desired user's SNR < 0 dB. With an estimate scheme of the desired user code, the proposed method offers more robustness against spreading code mismatch. Computer simulations show that the effectiveness of the proposed detector.

Hash routing is an algorithm for a distributed WWW caching system that achieves a high hit rate by preventing overlaps of objects between caches. However, one of the drawbacks of hash routing is its lack of robustness against failure. Because WWW becomes a vital service on the Internet, the capabilities of fault tolerance of systems that provide the WWW service come to be important. In this paper, we propose a duplicated hash routing algorithm, an extension of hash routing. Our algorithm introduces minimum redundancy to keep system performance when some caching nodes are crashed. In addition, we optionally allow each node to cache objects requested by its local clients (local caching), which may waste cache capacity of the system but it can cut down the network traffic between caching nodes. We evaluate various aspects of the system performance such as hit rates, error rates and network traffic by simulations and compare them with those of other algorithms. The results show that our algorithm achieves both high fault tolerance and high performance with low system overhead.

The reconfiguration latency defined as the time taken for reconfiguring a system upon failure detection or mode change. We evaluate it quantitatively for backup sparing, which is one of the most popular reconfiguration methods, by investigating the effects of key parameters.