This paper presents a new approach based on current mode circuits for fast and accurate optical level monitoring with wide dynamic range of a gigabit burst-mode laser driver chip. Our proposed solution overcomes the drawbacks that voltage mode implementations show at higher bit rates or in other technologies. The main speed-limiting factor of the level monitoring circuitry is the parasitic capacitance of the back facet monitor photodiode. We propose the use of an active-input current mirror to reduce the impact of this parasitic capacitance. The mirror produces two copies of the photo current, one to be used for the "0" level measurement and another for the "1" level measurement. The mirrored currents are compared to two reference currents by two current comparators. Every reference current needs only one calibration at room temperature. A pattern detection block scans the incoming data for patterns of sufficiently long consecutive 0's or 1's. At the end of such a pattern a valid measurement is present at the output of one of the current comparators. Based on these measurements the digital Automatic Power Control (APC) will adjust the bias (IBIAS) and modulation current (IMOD) setting of the laser driver. Tests show that the chip can stabilize and track the launched optical power with a tolerance of less than 1 dB. In these tests the pattern detection was programmed to sample the current comparators after 5 bytes (32 ns at 1.25 Gbps) of consecutive 1's and 0's. Automatic power control on such short strings of data has not been demonstrated before. Although this laser transmitter was developed for FSAN GPON applications at a speed of 1.25 Gbps upstream, the design concept is generic and can be applied for developing a wide range of burst mode laser transmitters. This chip was developed in a 0.35 µm SiGe BiCMOS process.

The enlargement of the left lobe of the liver and the shrinkage of the right lobe are helpful signs at MR imaging in diagnosis of cirrhosis of the liver. To investigate whether the volume ratio of left-to-whole (LTW) is effective to differentiate cirrhosis from a normal liver, we developed an automatic algorithm for three-dimensional (3D) segmentation and volume calculation of the liver region in multi-detector row CT scans and MR imaging. From one manually selected slice that contains a large liver area, two edge operators are applied to obtain the initial liver area, from which the mean gray value is calculated as threshold value in order to eliminate the connected organs or tissues. The final contour is re-confirmed by using thresholding technique. The liver region in the next slice is generated by referring to the result from the last slice. After continuous procedure of this segmentation on each slice, the 3D liver is reconstructed from all the extracted slices and the surface image can be displayed from different view points by using the volume rendering technique. The liver is then separated into the left and the right lobe by drawing an inter-segmental plane manually, and the volume in each part is calculated slice by slice. The degree of cirrhosis can be defined as the ratio of volume in these two lobes. Four cases including normal and cirrhotic liver with MR and CT slices are used for 3D segmentation and visualization. The volume ratio of LTW was relatively higher in cirrhosis than in the normal cases in both MR and CT cases. The average error rate on liver segmentation was within 5.6% after employing in 30 MR cases. These results demonstrate that the performance in our 3D segmentation was satisfied and the LTW ratio may be effective to differentiate cirrhosis.

The lithography process on the deep trench pattern above the large cavity is proposed to fabricate the MEMS structure. Generally, bubbles generated on the trench patterns when it was baked after coating resist. The probability of the generation of bubbles was reduced by decreasing the backing rate. The fast scanning micromirror with 50.8 kHz resonant frequency was fabricated by controlling the backing rate.

In this paper we propose a parallel and distributed computation of genetic local search with irregular topology in distributed environments. The scheme we propose in this paper is implemented with a tree topology established on an irregular network where each computing element carries out genetic local search on its own chromosome set and communicates with its parent when the best solution of each generation is updated. We evaluate the proposed algorithm by a simulation system implemented on a PC-cluster. We test our algorithm on four types topologies: star, line, balanced binary tree and sided binary tree, and investigate the influence of communication topology and delay on the evolution process.

We propose a simple method for the chromatic dispersion measurement of optical fibers by using bi-directional modulation of a Mach-Zehnder electro-optical modulator embodied in a fiber loop mirror. The detected output of the bi-directionally modulated light, with time difference, creates fading in the RF domain. Dispersion is found by measuring the period of fading at different wavelengths.

This investigation proposes a new multiplication algorithm in the finite field GF(2m) over the polynomial basis, in which the irreducible xm +xn + 1 with gcd(m,n) = 1 generates the field GF(2m). The algorithm involves two steps--the intermediate multiplication and the modulo reduction. In the first step, the intermediate multiplication algorithm permutes a polynomial to construct the full-bit-parallel systolic intermediate multiplier. The circuit is identical of m2 cells, each cell is identical of one 2-input AND gate, one 2-input XOR gate, and four 1-bit latches. In the second step, based on the results of the intermediate multiplication in the first step, the modulo reduction circuit is built using regular and simple reduction operations. The latency of the proposed multiplier requires m + k + 1 clock cycles, where k = + 1. Notably, the latency can be very low if n is in the range 1 n . For the computing multiplication in GF(2m), the novel multiplier exhibits much lower latency than the existing systolic multipliers, and is well suited to VLSI systems due to their regular interconnection pattern, modular structure and fully inherent parallelism.

Recently six conjectures on linear complexities (LC) of some Kronecker sequences of two or three component sequences are proposed by Karkkainen. In, the LC of Kronecker sequences of two component sequences were studied by Uehara and Imamura, their results are true except in the case when eb 2 or when ea = eb = 1. In this paper the LC for Kronecker sequences of two component sequences are determined completely, and it is shown that all the six conjectures are true except in some special cases, which are listed and corrected.

As so many software titles are now being distributed via the Internet, the number of accesses to file servers, such as FTP servers, is rapidly increasing. To prevent the concentration of accesses to the original file server, mirror servers are being introduced that contain the same directories and files as held by the original server. However, inconsistency among the mirror servers and the original server is often observed because of delivery latency, traffic congestion on the network, and management policies of the mirror servers. This inconsistency degrades the value of the mirror servers. Accordingly, we have developed an intermediate FTP proxy server system that guarantees the freshness of the files as well as preventing access concentration on the original FTP server. The system adopts per-file selection of the replicated files; most existing methods are based on per-host or per-directory selection. Therefore it can assure users of a quick, stable, and up-to-date FTP mirroring service even in the face of frequent content updates, which tend to degrade the homogeneity of services. Moreover, it can forward the retrieved files with little overhead. Tests confirmed that our system is comparable to existing systems from the viewpoint of actual retrieval time, required traffic, and load endurance. This technology can assure clients that they will receive the latest version of the file(s) desired. It well supports heterogeneous network environments such as the Internet.

Richardson and Urbanke developed a powerful method density evolution which determines, for various channels, the capacity of irregular low-density parity-check code ensembles. We develop generalized density evolution for minutely represented ensembles and show it includes conventional representation as a special case. Furthermore, we present an example of code ensembles used over binary erasure channel and binary input additive white Gaussian noise channel which have better thresholds than highly optimized ensembles with conventional representation.

As a lot of programs and contents such as movie files are being delivered via the Internet, and copies are often stored in distributed servers in order to reduce the load on the original servers, to ease network congestion, and to decrease response time. To retrieve an object file, existing methods simply select one or more servers. Such methods divide a file into equal pieces whose size is determined a priori. This approach is not practical for networks that offer variable bandwidth. In order to more utilize variable bandwidth, we propose an adaptive downloading method. We evaluate it by experiments conducted on the Internet. The results show that the new method is effective and that it will become an important network control technology for assurance.

In most cases of distributed memory computations, node programs are executed on processors according to the owner computes rule. However, owner computes rule is not best suited for irregular application codes. In irregular application codes, use of indirection in accessing left hand side array makes it difficult to partition the loop iterations, and because of use of indirection in accessing right hand side elements, we may reduce total communication by using heuristics other than owner computes rule. In this paper, we propose a communication cost reduction computes rule for irregular loop partitioning, called least communication computes rule. We partition a loop iteration to a processor on which the minimal communication cost is ensured when executing that iteration. Then, after all iterations are partitioned into various processors, we give global vs. local data transformation rule, indirection arrays remapping and communication optimization methods. The experimental results show that, in most cases, our approaches achieved better performance than other loop partitioning rules.

We propose a scheme for the design of irregular low-density parity-check (LDPC) codes based on Euclidian Geometry using Latin square matrices of random sequence. Our scheme is a deterministic method that allows the easy design of good irregular LDPC codes for any code rate and degree distribution. We optimize the LDPC codes using the Gaussian approximation method. A Euclidean Geometry LDPC code (EG-LDPC) is used as the basis for the construction of an irregular LDPC code. The base EG-LDPC code is extended by splitting rows and columns using a table of Latin square matrices of random sequence to determine the edges along which to split. We provide simulation results for codes constructed in this manner evaluated in terms of bit error rate (BER) performance in AWGN channels. We believe that our scheme is superior in terms of computational requirements and resulting BER performance in comparison to creation of irregular LDPC codes by means of random construction using a search algorithm to exclude cycles of length four.

In this paper, we will show that some families of periodic sequences over Z4 and Z8 with period multiple of 2r-1 generated by r-th degree basic primitive polynomials assorted by the root of each polynomial, and give the exact distribution of sequences for each family. We also point out such an instability as an extreme increase of their linear complexities for the periodic sequences by one-symbol substitution, i.e., from the minimum value to the maximum value, for all the substitutions except one.

We propose a new scheme of indoor optical wireless LAN based on a special CMOS image sensor (CIS), which realizes a low-power compact communication module with large uplink capacity due to space division multiple access. In our scheme, all nodes and a hub utilize the CIS as a photoreceiver as well as a position-sensing device for finding the positions of the communication modules, while a single large photodiode is used in the conventional systems. Although conventional image sensors cannot detect modulated signals because they integrate photocurrents, our CIS has a high-speed readout function for receiving optical data from the specific pixels receiving optical signals. The advantages of the proposed scheme are 1) compact embodiment of the communication module due to no need of the bulky mechanical components for searching the other modules, 2) space division multiple access, which leads to 3) large capacity of uplink, and 4) applicability of simple modulation and coding schemes for optical signals. In our scheme, diffusive and narrow beam lights are complementally used for position detection and communication, respectively, which leads to the advantage 5) low power consumption of both light emitter and receiver circuits. To demonstrate two basic functional modes of our CIS: an IS (image sensor) mode and a COM (communication) mode, we fabricate an 88-pixel CIS by use of a 0.8µm BiCMOS technology. In the experiments, the image of a light source is successfully captured in the IS mode for integration time of 29.6msec and optical power of 1.1nW. After the functional mode of the pixel receiving the light is changed to the COM mode, the eye pattern of the modulated light is obtained from the pixel at frequency of 1MHz. We also fabricate a test pixel circuit with in-pixel amplifier, with which operation speed is improved to 100MHz.

Mirroring of network servers has been considered to be effective for load balancing. However, the cost of setting up new mirror servers is enormously high. In this paper, we propose a dynamic file allocation model with a simple mirroring function for handling significant changes of network traffic in the Internet. According to the load fluctuation, we can dynamically reallocate files using this model. We show that our model accomplishes satisfactory performance and reduces cost by adding a simple mirroring function to all existent servers instead of setting up mirror servers afresh.

We have classified parenchymal echo patterns of cirrhotic liver into four types, according to the size of hypo echoic nodular lesions. The NN (neural network) technique has been applied to the characterization of hepatic parenchymal diseases in ultrasonic B-scan texture. We employed a multilayer feedforward NN utilizing the back-propagation algorithm. We extracted 1616 pixels in the two-dimensional regions. However, when a large area is used, input data becomes large and much time is needed for diagnosis. In this report, we used DCT (discrete cosine transform) for the feature extraction of input data, and compression. As a result, DCT was found to be suitable for compressing ultrasonographic images.

In the Internet, the routing system consists of the Interior-domain and the Inter-domain. Within the Inter-domain routing, Autonomous System (AS) represents the administrative network domain, which is managed by a single institution with its operational policy. ASs exchange the ASs' reachability information to each other. Without the Inter-domain routing scheme, the nodes in the Internet can't communicate across the multiple ASs. The Inter-domain routing is an essential functional element in the global Internet operation. However, due to several reasons such as miss-configuration at the routers, the Inter-domain routing becomes unstable. This occurs that one AS (say AS1) propagates the prefix that has been already assigned to another AS (say AS2) and other peers receive its routing update and inject the misconfigured AS information to their peering routers. Since the routing information associated with AS1 is over written by AS2, AS1 loses the network connectivity. This problem is known as the Conflict Origin AS prefix or the Multiple Origin AS. We recognize that this is a serious problem which degrades the quality of Internet backbone infrastructure. We focus on this problem and propose the mechanism that can detect the Conflict Origin AS prefix automatically using the policy database. Based on the evaluation using the prototype system, we demonstrate that the proposed mechanism can work well with the existing Internet's Inter-domain routing system.

Server performance is a major issue in improving the overall performance of the World Wide Web (WWW). This article introduces a dynamic mirroring-based approach to improve WWW servers' performance. In contrast to static mirroring, where mirror servers are allocated statically, our mirror servers' setup is driven by network traffic measurement. Performance in terms of latency is inferred from a queuing model. According to this model we show that latency of an overloaded server can be tuned by delegating a portion of the load to a cooperative mirror server. Cost is evaluated by the amount of load hosted by the mirror servers. The goal is then to keep the latency within a tolerable threshold, while minimizing the delegated load. This problem is formulated as a constrained optimization problem where the task is to assign a portion of load corresponding to each document to each mirror server. As the result of this work, we will have a balanced load among the servers, and a smoother traffic along the Internet, as well. Empirical results show that this approach can guarantee to maintain the performance while showing a significant decrease in the amount of load transferred to the mirror servers.

Network traffic characteristics impacts directly network performance, and resource allocation policies. In this work, we introduce a multi-agent system, that manages the performance of web servers with minimal cost of mirroring. In our proposed system each web server is viewed as a software agent that perceives its environment by monitoring its traffic. The goal of the agent is to manage the performance, using cooperative mirror servers, while minimizing the cost of mirroring. Communication between the agents enables each web server to decide about its future actions, which is whether to share its load with the cooperative mirror servers, and how much load to assign to them. The architecture of a software agent that is intended to manage the performance of a web server, is elaborated and its different modules are described. Also a set of cooperative agents is defined, that form a multi-agent system and is intended to assure maintaining the performance with minimal cost of mirroring. The experimental results presented in this article illustrates the effectiveness of the proposed system.

In this paper, we consider optimal mirror allocation problems for the purpose of load balancing in network servers. We focus on constructing high-reliability networks and propose the optimal mirror allocation model such that the system reliability is maximized subject to costs and delays, in view of the trade-off between the reliability and cost. This optimization model is capable of dealing with various kinds of network topologies, although for simplicity, we assume the read-only situation. We formulate this optimization problem into a 0-1 integer programming model, and we use an approximate method for numerical analysis in order to analyze more large-scale systems. Our objective is to find the optimal mirror allocation by solving this model, and to show quantitatively the general characteristics of the load balancing and the improvement of the system reliability by the distributed mirror allocation.