A simple configuration for millimeter-wave fiber-wireless transmission, with remote local-oscillator (LO) delivery from the central office, both for the uplink and for the downlink, and a simple, cost-effective, base-station solution is proposed. Under the assumption of using commercially available components and a conventional single-mode fiber (with dispersion of 17 ps/nm/km at 1.55 µm), our numerical results show that, with a laser linewidth of 150 MHz, a laser power of 0 dBm and an optical gain of only 6 dB, it is possible to transmit, without repeaters, data rates of 622 Mbit/s across about 18 km at a bit-error-rate of 10-9. By increasing the optical gain to 24 dB, the link length can be increased to approximately 67 km for a laser linewidth of 75 MHz and to 78 km for a laser linewidth 1 MHz.

This paper deals with the wave scattering from a periodic surface with finite extent. Modifying a spectral formalism, we find that the spectral amplitude of the scattered wave can be determined by the surface field on only the corrugated part of the surface. The surface field on such a corrugated part is then expanded into Fourier series with unknown Fourier coefficients. A matrix equation for the Fourier coefficients is obtained and is solved numerically for a sinusoidally corrugated surface. Then, the angular distribution of the scattering, the relative power of each diffraction beam and the optical theorem are calculated and illustrated in figures. Also, the relative powers of diffraction are calculated against the angle of incidence for a periodic surface with infinite extent. By comparing a finite periodic case with an infinite periodic case, it is pointed out that relative powers of diffraction beam are much similar in these of diffraction for the infinite periodic case.

With the advance of high-speed network technologies, availability and popularity of streaming media contents over the Internet has grown rapidly in recent years. Because of their distinct statistical properties and user viewing patterns, traditional delivery and caching schemes for normal web objects such as HTML files or images can not be efficiently applied to streaming media such as audio and video. In this paper, we therefore propose an integrated caching scheme for streaming media with segment-based caching and hierarchically distributed proxies. Firstly, each stream is divided into segments and their caching algorithms are considered to determine how to distribute the segments into different level proxies efficiently. Secondly, by introducing two kinds of segment priorities, segment replacing algorithms are proposed to determine which stream and which segments should be replaced when the cache is full. Finally, a Web-friendly caching scheme is proposed to integrate the streaming caching with the conventional caching of normal web objects. Performance of the proposed algorithms is verified by carrying out simulations.

A reconfigurable network interface called RHiNET-2/NI0 is developed for parallel processing of PCs distributed within one or more floors of a building. Two configurations: the HS (High Speed) configuration with only a high-speed primitive and the DSM (Distributed Shared Memory) configuration which supports sophisticated primitives can be selected by the network requirement. From the empirical evaluation, it appears that the HS configuration markedly improves the latency of data transfer compared with traditional network interfaces. On the other hand, the DSM configuration executes sophisticated primitives for distributed shared memory more than twice as fast as that of software implementation.

Multi-channel arrayed waveguide devices are crucial for WDM optical communication systems. Multi-channel arrayed polymer-based waveguide devices have been important for reducing cost and size. This paper introduces two types of multi-channel arrayed polymer-based waveguide devices. We designed and fabricated a four-channel arrayed 22 thermo-optic switch using a low-loss polymer and a four-channel arrayed electro-optic Mach-Zehnder modulator using an electro-optic polymer. The four-channel arrayed 22 thermo-optic switch has very low power consumption and uniform performance. The switching time of the four-channel arrayed EO Mach-Zehnder modulator operating with just lumped electrodes is less than a few nanoseconds.

WASMII is a virtual hardware system that executes dataflow algorithms using a dynamically reconfigurable multi-context device with a data driven control mechanism. Although the effectiveness of the system has been evaluated through simulations and using an emulator, implementation of WASMII was infeasible due to the unavailability of such a device. However, the first prototype of a practical dynamically reconfigurable multi-context device called DRL has been developed by NEC, and we developed a reconfigurable test bed using four sample DRL chips. On this board, we have implemented and executed some simple applications of WASMII mechanism. Evaluation results show that the performance of the parallel implementation of WASMII is almost twice as that of a PC with a CPU based on the corresponding technology.

Caching web files reduces user response time as well as network traffic. When implementing caches, the file caching problem must be addressed; the problem is how to determine which files should be evicted from a cache when there is insufficient space for storing a new file so that the sum of the mis-hit (fault) file costs is minimized. Greedy-Dual-Size (GDS) is the best online algorithm in terms of competitiveness, i. e. , (k)/(k-h+1)-competitive, where k and h are the storage space of, respectively, GDS and an optimal offline algorithm. GDS performs very well even in trace-driven simulations. The worst-case time taken to service a request is another important measure for online file caching algorithms since slow response times render caching meaningless from the client's view point. This paper proposes a fast randomized (k)/(k-h+1)-competitive algorithm that performs in O(2log ^* k) time per file eviction or insertion, whereas GDS takes O(log k) time, where 2log ^* k is a much slower increasing function than log k. To confirm its practicality, we conduct trace driven simulations. Experimental results show that our algorithm attains only slightly worse byte hit rates and sufficiently large reduced latency in comparison with GDS, and our algorithm is a good candidate for caches requiring high-speed processing such as second-level caches in the large networks.

In recent computer systems, a large portion of energy is consumed by on-chip cache accesses and data movement between cache and off-chip main memory. Reducing these memory system energy is indispensable for future microprocessors because power and thermal issues certainly become a key factor of limiting processor performance. In this paper, we discuss and evaluate how our architecture called SCIMA contributes to energy saving. SCIMA integrates software-controllable memory (SCM) into processor chip. SCIMA can save total memory system energy by using SCM under the support of compiler. The evaluation results reveal that SCIMA can reduce 5-50% of memory system energy and still faster than conventional cache based architecture.

Buffer caching is an integral part of the operating system. In this paper, we propose a scheme that integrates buffer cache management and prefetching via cache partitioning. The scheme, which we call SA-W2R, is simple to implement, making it a feasible solution in real systems. In its basic form, for buffer replacement, it uses the LRU policy. However, its modular design allows for any replacement policy to be incorporated into the scheme. For prefetching, it uses the LRU-One Block Lookahead (LRU-OBL) approach, eliminating any extra burden that is generally necessary in other prefetching approaches. Implementation studies based on the GNU/Linux kernel version 2.2.14 show that the SA-W2R performs better than the scheme currently used, with a maximum increases of 23% for the workloads considered.

In the Internet, flow analysis and network monitoring have been studied by various methods. Some methods try to make TCP (Transport Control Protocol) traces more readable by showing them graphically. Others such as MRTG, NetScope, and NetFlow read the traffic counters of the routers and record the data for traffic engineering. Even if all of the above methods are useful, they are made only to perform a single task. This paper describes an improved TCP Protocol Machine, a multipurpose tool that can be used for flow analysis, intrusion detection and link congestion monitoring. It is developed based on a finite state machine (automaton). The machine separates the flows into two main groups. If a flow can be mapped to a set of input symbols of the automaton, it is valid, otherwise it is invalid. It can be observed that intruders' attacks are easily detected by the use of the protocol machine. Also link congestion can be monitored, by measuring the percentage of valid flows to the total number of flows. We demonstrate the capability of this tool through measurement and working examples.

This paper investigates properties of space-bounded "two-dimensional Turing machines (2-tm's)," whose input tapes are restricted to square ones, with bounded input head reversals in vertical direction. We first investigate a relationship between determinism and nondeterminism for space-bounded and input head reversal-bounded 2-tm's. We then investigate how the number of input head reversals affects the accepting power of sublinearly space-bounded 2-tm's. Finally, we investigate necessary and sufficient spaces for three-way 2-tm's to simulate four-way two-dimensional finite automata with constant input head reversals.

This paper describes a method for assessing the structural integrity of International America's Cup Class (IACC) yachts using a fiber optic distributed strain sensor. IACC yachts are made of advanced composite materials designed for high stiffness and lightness, however, a number of critical accidents have occurred during sailing. So we developed a health monitoring system and applied it to two Japanese IACC yachts to measure the distributed strain by using an optical fiber sensor installed in their hulls. We then estimated the three-dimensional distributed strain and compared the results with simulated data obtained by finite element analysis (FEA) to confirm the designed strength of these yachts.

We propose an enhanced packet access scheme for IMT-2000/UMTS random access channel (RACH). In the proposed scheme, 2-level preamble detection threshold and 2-level message transmission power are used to mitigate the power imbalance in RACH. Simulation results demonstrate that the proposed scheme improves the interference characteristics of the conventional RACH and makes wider range of the detection threshold available.

This paper proposes and investigates a coding and decoding scheme to achieve adaptive channel coding using a Finite State Machine (FSM) for Software Defined Radio (SDR). Adaptive channel coding and decoding systems that can switch between different coding rates and error correcting capabilities in order to adapt to changing applications and environments, are effective for SDR. However, in these systems, a receiver cannot always select the correct decoder which causes decoding errors, usually referred to as Decoder-Selection-Errors (DSE). We propose a trellis encoder estimation scheme that compensates for this problem. This scheme uses the circuit of FSM to limit the encoder transition and the Viterbi algorithm for maximum likelihood trellis encoder estimation. Computer simulations are applied for evaluating the DSE rate, the Bit Error Rate (BER) and Throughput of the proposed scheme in comparison with a conventional scheme.

This paper presents a method for disambiguating word senses in Korean-Japanese machine translation by using a language independent ontology. This ontology stores semantic constraints between concepts and other world knowledge, and enables a natural language processing system to resolve semantic ambiguities by making inferences with the concept network of the ontology. In order to acquire a language-independent and reasonably practical ontology in a limited time and with less manpower, we extend the existing Kadokawa thesaurus by inserting additional semantic relations into its hierarchy, which are classified as case relations and other semantic relations. The former can be obtained by converting valency information and case frames from previously-built electronic dictionaries used in machine translation. The latter can be acquired from concept co-occurrence information, which is extracted automatically from a corpus. In practical machine translation systems, our word sense disambiguation method achieved an improvement of average precision by 6.0% for Japanese analysis and by 9.2% for Korean analysis over the method without using an ontology.

This paper presents a comprehensive investigation of three optical wavelength-division multiplexed (WDM) mesh network protection approaches, namely minimal cost, single link basis and disjoint path approaches. The operation of each approach is described and their performances are extensively evaluated and compared. Key aspects that are taken into the consideration and comparison of the designs include a spare capacity requirement, ease of operation and practical feasibility. A mathematical model based on integer linear programming is introduced to obtain a lower bound on the spare capacity requirement for full protection against all single link failures. Two heuristic algorithms have also been developed to perform wavelength resource allocation under both normal and failure conditions for both systems with and without wavelength conversion capability. It is shown that the minimal cost approach can accomplish the lowest extra cost requirement for protection, but this approach is considered not appropriate for practical applications due to complicated restoration and management. The single link basis scheme is on the other hand more practical and very cost efficient. For the disjoint path technique, the cost for spare capacity is generally slightly greater than that of the single link basis scheme. Its main advantages lie in the simple re-configuration and inherent protection against node failure for in-transit traffic. Finally, a new framework for obtaining a good spare capacity cost estimate of a mesh restorable network is presented.

A procedure to remove redundancies in sequential circuits is proposed using strongly unreachable states, which are the states with no incoming transitions. Test generation is used to find undetectable faults related to two or more strongly unreachable states. Experimental results show the new procedure can find more redundancies of sequential circuits.

Caching of frequently accessed data has been shown to be a useful technique for reducing congestion on the narrow bandwidth of wireless channels. However, traditional client/server strategies for supporting transactional cache consistency, which require extensive communications between a client and a server, are not appropriate in a wireless mobile database. This paper proposes two, simple but effective, transactional cache consistency protocols for mobile read-only transactions by utilizing the broadcast-based solutions for the problem of invalidating caches. The novelty of our approach is that the consistency check on accessed data and the commitment protocol are implemented in a truly distributed fashion as an integral part of cache invalidation process. The applicability of proposed techniques is also examined by an analytical study.

This paper investigates the stochastic property of packet destinations in order to describe Internet access patterns. If we assume a sort of stationary condition for the address generation process, the process is an LRU stack model. Although the LRU stack model gives appropriate descriptions of address generation on a medium/long time-scale, address sequences generated from the LRU stack model do not reproduce Zipf-type distributions, which appear frequently in Internet access patterns. This implies that the address generation behavior on a short time-scale has a strong influence on the shape of the distributions that describe frequency of address appearances. This paper proposes an address generation algorithm that does not meet the stationary condition on the short time-scale, but restores it on the medium/long time-scale, and shows that the proposed algorithm reproduces Zipf-type distributions.

On the basis of generalized theory of system design the behavior of the different design trajectories in the design phase space was analyzed. An additional acceleration effect of the design process has been discovered by the analysis of various design strategies with different initial points. This effect can be understood well on the basis of the elaborated design methodology by means of the different design trajectory analysis. This effect is displayed for all analyzed circuits and it reduces additionally the total computer time for the system design.