Our recent progress in improving the performance of the GaInNAs laser is fully reviewed here. We improved the crystal quality of GaInNAs by optimizing the conditions for its grown by gas-source molecular beam epitaxy (MBE) using N radicals as a N source. We found that the temperature window for obtaining GaInNAs with high crystal quality, good surface morphology, and good photoluminescence (PL) characteristics is smaller than that for obtaining this kind of GaInAs. Like dopant atoms such as Si or Be in GaAs, the N radicals produced by an RF discharge have a high sticking coefficient. Their use is therefore effective when we want to increase and control the N content of GaInNAs. We found that the AsH3-flow-rate mainly affected crystal quality of GaInNAs rather than incorporation of nitrogen atoms. We also investigated the effects of thermal annealing on the optical properties of as-grown GaInNAs layers and found that it greatly increased the PL intensity and produced the large shift in the PL wavelength. The absorption spectra of the GaInNAs bulk layer revealed that the large shift in the PL wavelength is probably caused by a bandgap shift in the GaInNAs well layer, and cathodeluminescence measurements revealed that the increased PL intensity is due to the improved emission being more uniform spatially: uniformity from the entire region; in comparison, nonuniform dot-like regions exist in an as-grown GaInNAs layer. Optimizing the growth conditions and using thermal annealing effect, we made a 1.3-µm GaInNAs/GaAs single-quantum-well laser that has a high characteristic temperature (215 K) under pulsed operation. To our knowledge, this is the highest characteristic temperature reported for a 1.3-µm band-edge emitter suitable for used in optical-fiber communication systems. The use of GaInNAs as an active layer is, therefore, very promising for the fabrication of long-wavelength laser diodes with excellent high-temperature performance.

A rigorous modal approach based on the transmission-line description has developed to explore effectively the filtering characteristics of planar optical DFB guiding structures. Using the modal transmission-line theory, the leakage and filtering characteristics of metal-strip gratings and dielectric gratings with gain or loss are first evaluated in details at the first- and third-order Bragg regimes. It can thus serve as a powerful template for computational algorithms to determine systematically and rigorously the optical effects of multilayered periodic guiding structures, which are not readily obtained by other methods.

This paper proposes a private communication system with chaos using fixed-point digital computation. When fixed-point computation is adopted, chaotic properties of the modulated signal should be checked carefully as well as calculation error problems (especially, overflow problems). In this paper, we propose a novel chaos modem system for private communications including a chaotic neuron type nonlinearity, an unstable digital filter and an overflow function. We demonstrate that the modulated signal reveals hyperchaotic property within 10,000 data point fixed-point computation, and evaluate the security of this system in view of the sensitivity of coefficients for demodulation.

Interference suppression is one of the important functions for mobile communications and software radio. First, this paper shows a new type of interference suppression method by P-RCE (Probability-Restricted Coulomb Energy) which is applicable to mobile communications and software radio. P-RCE is one of the neural networks and mainly used in the field of pattern classification. Secondly, this paper presents several characteristics of this method. For example, it is found from our studies that good suppression effects can be performed even when the interference signals exist closely adjacent to the desired signal and/or total number of signals is more than that of the antenna elements. Next, this paper discusses two types of improvement of processing speed for new suppression method. One is the setting up the learning and non-learning intervals, and the other is the restriction of the number of prototype cells. According to the results, fairly good improvement is realized.

The conventional back-propagation algorithm cannot be applied to networks of units having hard-limiting output functions, because these functions cannot be differentiated. In this paper, a gradient descent algorithm suitable for training multilayer feedforward networks of units having hard-limiting output functions, is presented. In order to get a differentiable output function for a hard-limiting unit, we utilized that if the bias of a unit in such a network is a random variable with smooth distribution function, the probability of the unit's output being in a particular state is a continuously differentiable function of the unit's inputs. Three simulation results are given, which show that the performance of this algorithm is similar to that of the conventional back-propagation.

In a decentralised system the problems of fault tolerance, and in particular error recovery, vary greatly depending on the design assumptions. For example, in a distributed database system, if one disregards the possibility of undetected invalid inputs or outputs, the errors that have to be recovered from will just affect the database, and backward error recovery will be feasible and should suffice. Such a system is typically supporting a set of activities that are competing for access to a shared database, but which are otherwise essentially independent of each other--in such circumstances conventional database transaction processing and distributed protocols enable backward recovery to be provided very effectively. But in more general systems the multiple activities will often not simply be competing against each other, but rather will at times be attempting to co-operate with each other, in pursuit of some common goal. Moreover, the activities in decentralised systems typically involve not just computers, but also external entities that are not capable of backward error recovery. Such additional complications make the task of error recovery more challenging, and indeed more interesting. This paper provides a brief analysis of the consequences of various such complications, and outlines some recent work on advanced error recovery techniques that they have motivated.

The homogeneous structure of field programmable gate arrays (FPGAs) suggests that the defect tolerance can be achieved by shifting the configuration data inside the FPGA. This paper proposes a new approach for tolerating the defects in FPGA's configurable logic blocks (CLBs). The defects affecting the FPGA's interconnection resources can also be tolerated with a high probability. This method is suited for the makers, since the yield of the chip is considerably improved, specially for large sizes. On the other hand, defect-free chips can be used as either maximum size, ordinary array chips or fault tolerant chips. In the fault tolerant chips, the users will be able to achieve directly the fault tolerance by only shifting the design data automatically, without changing the physical design of the running application, without loading other configurations data from the off-chip FPGA, and without the intervention of the company. For tolerating defective resources, the use of spare CLBs is required. In this paper, two possibilities for distributing the spare resources (king-shifting and Horse-allocation) are introduced and compared.

This paper presents a new design for testing SRAM-based field programmable gate arrays (FPGAs). The original FPGA's SRAM memory is modified so that the FPGA may have the facility to loop the testing configuration data inside the chip. The full testing of the FPGA is achieved by loading typically only one carefully chosen testing configuration data instead of the whole configurations data. The other required configurations data are obtained by shifting the first one inside the chip. As a result, the test becomes faster. This method does not need a large off-chip memory for the test. The evaluation results prove that this method is very effective when the complexity of the configurable blocks (CLBs) or the chip size increases.

The SDP (Sum of Disjoint Products) approach is a well-known technique for computing network reliability measures. So far several algorithms have been developed based on this approach. In this letter, we present a general framework for parallelization of these SDP algorithms. Based on the framework, we implemented a parallel version of an SDP algorithm called CAREL on a network of workstations. Experimental results show that it works fairly well with almost linear speedups.

A min-wise independent permutation family is known to be an efficient tool to estimate similarity of documents. Toward good understanding of min-wise independence, we present a characterization of exactly min-wise independent permutation families by size uniformity, which represents certain symmetry of the string representation of a family. Also, we present a general construction strategy which produce any exactly min-wise independent permutation family using this characterization.

A family C of min-wise independent permutations is known to be a useful tool of indexing replicated documents on the Web. For any integer n>0, a family C of permutations on [n]={1,2,. . . ,n} is said to be min-wise independent if for any (nonempty) X [n] and any x X, Pr ( min {π(X)} = π(x))= ||X||-1 when π is chosen uniformly at random from C, where ||A|| is the cardinality of a finite set A. For any integer n>0, it has been known that (1) ||C|| lcm(n,n-1,. . . ,2,1) = en-o(n) for any family C of min-wise independent permutations on [n]; (2) there exists a polynomial time samplable C family of min-wise independent permutations on [n] such that ||C|| 4n. However, it has been unclear whether there exists a min-wise independent family C such that ||C|| = lcm(n,n-1,. . . ,2,1) for each integer n>0 and how to construct such a family C of min-wise independent permutations for each integer n>0 if it exists. In this paper, we shall construct a family Fn of permutations for each integer n>0 and show that Fn is min-wise independent and ||Fn|| = lcm(n,n-1,. . . ,2,1). Moreover, we present a polynomial time sampling algorithm for the family. Thus the family Fn of min-wise independent permutations is optimal in the sense of family size and is easy to implement because of its polynomial time samplability.

This paper presents an object-oriented model to handle the temporal relationship for all of the multimedia objects at the presentation platform. Synchronization of the composite media objects is achieved by ensuring that all objects presented in the upcoming "manageable" period must be ready for execution. To this end, the nature of overlays is first investigated for various types of objects. Critical overlaps which are crucial in synchronization are also defined. The objective of synchronization is to ensure that the media objects can be initiated precisely at the critical point of the corresponding critical overlap. The concept of manageable presentation interval is introduced and the irreducible media group is defined. The resource scheduling of each presentation group for media object pre-fetch time versus buffer occupancy is also examined. Accordingly, a new model called group cascade object composition Petri-net (GCOCPN) is proposed and an algorithm to implement this temporal synchronization scheme is presented.

The relationship between the change in transistor operation regions and the fault behavior of a mixed-signal circuit having a bridging fault was investigated. We also discussed determination of transistors to be observed for estimating the fault behavior. These results will be useful for modeling faulty behaviors and analyzing and diagnosing faults in mixed-signal circuits.

This letter proposes a congestion control scheme for the ABR service of ATM networks which have non-responding connections. The control scheme is robust with respect to both the round trip delay and the loss of control information caused by non-responding connections. Thus, it is shown that the proposed control scheme guarantees the QoS of the network.

We first describe fundamental results about submodular functions and submodular flows, which lay a basis for devising efficient algorithms for submodular flows. We then give a comprehensive survey on algorithms for submodular flows and show some possible future research directions.

This paper demonstrates the slope isn't an appropriate parameter to characterize a signal regarding conducted electromagnetic disturbances. On the other hand, a relevant criterion is made conspicuous: it defines the maximum slope deviation between two segments forming a signal. This criterion is validated by a signal with a maximum slope of 400 mA/µs.

This paper presents a robust and nonblocking group membership protocol for large-scale distributed systems. This protocol uses the causal relation between membership-updating messages (i. e. , those specifying the adding and deleting of members) and allows the messages to be executed in a nonblocking manner. It differs from conventional group membership protocols in the following points: (1) neither global locking nor global synchronization is required; (2) membership-updating messages can be issued without being synchronized with each other, and they can be executed immediately after their arrival. The proposed protocol therefore is highly scalable, and is more tolerant to node and network failures and to network partitions than are the conventional protocols. This paper proves that the proposed protocol works properly as long as messages can eventually be received by their destinations. This paper also discusses some design issues, such as multicast communication of the regular messages, fault tolerance and application to reliable communication protocols (e. g. , TCP/IP).

Speech can be modeled as short bursts of vocal energy separated by silence gaps. During typical conversation, talkspurts comprise only 40% of each party's speech and remaining 60% is silence. Communication systems can achieve spectral gain by disconnecting the users from the spectral resource during silence periods. This letter develops a simple and efficient Voice Activity Detection (VAD) algorithm to work in a mobile environment exhibiting dynamically varying background noise. The VAD uses a classification method involving the full-band energy, ratio of low-band energy to full-band energy, zero-crossing rate, and peakiness measure.

Future high-speed switches and routers will be expected to support a large number of ports at high line rates carrying traffic with diverse statistical properties. Accordingly, scheduling mechanisms will be required to handle Tbit/sec aggregated capacity while providing quality of service (QoS) guarantees. In this paper a novel high-capacity switching scheme for ATM/WDM networks is presented. The proposed architecture is contention-free, scalable, easy to implement and requires no internal "speedup. " Non-uniform destination distribution and bursty cell arrivals are examined when studying the switching performance. Simulation results show that at an aggregated throughput of 1 Tbit/sec, low latency is achieved, yielding a powerful solution for high-performance packet-switch networks.

The performance of TCP/IP over ATM over an asymmetric digital subscriber line (ADSL) was investigated. Because the bandwidth of an ADSL link can vary over time due to changes in the link's physical conditions, which degrades TCP performance, we performed simulations for various ATM traffic controls, including available bit rate (ABR) and generic flow control, used to handle variations in the ADSL bandwidth. This analysis showed that using an ABR control is effective under various traffic conditions. An ABR switch algorithm that can achieve good performance under any condition was investigated.