We demonstrate, through numerical simulations, the possibility of trans-oceanic single channel transmission at 160 Gbit/s with no active control. This was achieved using short period dispersion management, which supports short pulse propagation at practical map strengths. We demonstrate that through careful selection and optimisation of the system parameters the performance of this system can be extended. We also define the tolerable limits of the system to the residual dispersion slope and polarisation mode dispersion.

The uniform switching system is the family of non-linear n m binary arrays constrained such that all columns are from the constant weight k vectors and all rows have weights divisible by p > 0. For this system, we present a cardinality formula and an enumerative algorithm.

In erbium doped optical fiber amplifiers (EDFAs) used in modern high-capacity wavelength division multiplexing (WDM) systems, the gain flatness of EDFA is very important in wide-band long-haul systems. In the EDFAs using the passive gain equalizers, the gain flatness deteriorates due to gain-tilt when the operating condition of the EDFA changes, while the EDFAs should maintain the gain flatness even if the operating condition has changed. To solve this problem, we have developed an active gain-slope compensation technique of an EDFA using a thulium-doped optical fiber (TDF) as a saturable absorber. The actively gain-slope compensated EDFA with the TDF compensator keeps the gain profile constant for the wide gain dynamic range more than 8 dB with the low noise figure less than 6 dB in the wavelength range of 1539-1564 nm.

In erbium doped optical fiber amplifiers (EDFAs) used in modern high-capacity wavelength division multiplexing (WDM) systems, the gain flatness of EDFA is very important in wide-band long-haul systems. In the EDFAs using the passive gain equalizers, the gain flatness deteriorates due to gain-tilt when the operating condition of the EDFA changes, while the EDFAs should maintain the gain flatness even if the operating condition has changed. To solve this problem, we have developed an active gain-slope compensation technique of an EDFA using a thulium-doped optical fiber (TDF) as a saturable absorber. The actively gain-slope compensated EDFA with the TDF compensator keeps the gain profile constant for the wide gain dynamic range more than 8 dB with the low noise figure less than 6 dB in the wavelength range of 1539-1564 nm.

We consider methods for threshold RSA decryption among distributed agencies without any dealer or trusted party. The first solution is a combination of two techniques by [9] and [7] . It demonstrates the feasibility of combining the distributed key generation and the RSA secure function application. The second solution is another approach making the distributed key distribution simpler and alleviating a burden of each shareholder in comparison with the first scheme. The latter scheme is newly developed technique based on [9] and further inspired by Simmons' protocol-failure of RSA (we believe that it is very interesting that a "protocol failure attack" be turned into a constructive method). Our comparison between these two schemes indicates a new measure of the performance of a distributed cryptographic protocol that consists of multiple stages.

Elliptic curve cryptosystems are based on the elliptic curve discrete logarithm problem (ECDLP). If elliptic curve cryptosystems avoid FR-reduction and anomalous elliptic curve over Fq, then with current knowledge we can construct elliptic curve cryptosystems over a smaller definition field. ECDLP has an interesting property that the security deeply depends on elliptic curve traces rather than definition fields, which does not occur in the case of the discrete logarithm problem (DLP). Therefore it is important to characterize elliptic curve traces explicitly from the security point of view. As for FR-reduction, supersingular elliptic curves or elliptic curve E/Fq with trace 2 have been reported to be vulnerable. However unfortunately these have been only results that characterize elliptic curve traces explicitly for FR- and MOV-reductions. More importantly, the secure trace against FR-reduction has not been reported at all. Elliptic curves with the secure trace means that the reduced extension degree is always higher than a certain level. In this paper, we aim at characterizing elliptic curve traces by FR-reduction and investigate explicit conditions of traces vulnerable or secure against FR-reduction. We show new explicit conditions of elliptic curve traces for FR-reduction. We also present algorithms to construct such elliptic curves, which have relation to famous number theory problems.

In an ideal fiber grating having a uniform refractive index modulation, the reflection or the transmission spectrum is symmetric with equal amount of side lobes on both sides of the resonant wavelength of the fiber grating. It is observed that a long-period fiber grating made by a non-uniform UV laser beam through a uniform amplitude mask has an asymmetric transmission spectrum. The asymmetric characteristic is explained with Mach-Zehnder effect in the long-period fiber grating. The non-uniform UV laser beam makes also a non-uniform index modulation along the fiber core. Therefore, a beam coupled to a cladding mode at a section of the grating can be re-coupled to the core mode after passing a certain distance. The re-coupled beam makes Mach-Zehnder-like interference with the un-coupled core mode. However, it is presented that the asymmetric phenomenon can be overcome by scanning the UV laser beam along the fiber over the mask. The beam scanning method is able to suffer the same fluence of the UV laser beam on the fiber. Finally, a linearly chirped long-period fiber grating was made using the non-uniform UV laser beam. Due to the asymmetricity the chirping effect was not clearly observed. It is also presented that the beam scanning method could remove the asymmetric problem and recover the typical spectrum of the linearly chirped fiber grating.

Arts and Giesl introduced the notion of dependency pairs, which gives effective methods for proving termination of term rewriting systems (TRSs). In this paper, we extend the notion to AC-TRSs, and introduce new methods for effectively proving AC-termination. It is impossible to directly apply the notion of dependency pairs to AC-TRSs. To avoid this difficulty, we introduce the notion of extended dependency pairs. Finally we define the AC-dependency pair and the AC-dependency chain. Furthermore, we propose approximated AC-dependency graphs, which is very useful for proving AC-termination in practice, using the approximation technique based on Ω-reduction and ΩV-reduction.

In order to realize automatic-level-controlled (ALC) erbium doped fiber amplifiers (EDFAs) with both wide dynamic range and good noise performance, we propose EDFAs employing the automatic power control (APC) scheme and a variable attenuation slope compensator (VASC). The VASC consists of two asymmetrical Mach-Zehnder interferometers (MZIs) concatenated in series and thermo optic (TO) heaters are attached to the arms of each MZIs. By adjusting the electric power supplied to the TO heaters, an almost linear attenuation slope can be varied by plus minus 5 dB or more over the operational wavelength band of 30 nm. The EDFA employing the APC scheme and the VASC has exhibited a dynamic range as large as 20 dB with the output power variation as small as 0.7 dB, which is as good as that of the EDFA employing the APC scheme and a variable optical attenuator (VOA). The noise figure (NF) of the EDFA employing the VASC was degraded about 4.1 dB with increasing the input power by 20 dB, while it was degraded about 7.3 dB with increasing the input power by only 15 dB in the EDFA employing the VOA. The EDFA employing the VASC can realize the ALC operation over a wider dynamic range with reduced noise figure degradation. In the EDFA employing the VASC, the power excursion was suppressed to less than 1.1 dB, when the input signal level was changed between -23 dBm/ch and -18 dBm/ch with the rise/fall time of 8 ms.

Highly reliable and high power weakly index guided buried-stripe type 980 nm pump laser diodes developed for undersea applications are reviewed. The 10,000-hour large scale reliability tests of the first generation LD chips shows that 16.7 FIT for the random failure was confirmed at 10C with 60% confidence level at 120 mW output power. We also fabricated a FBG locked co-axial type module using a can-sealed LD with a two-lens system, which showed a stable FBG locked mode oscillation at 980 nm under the temperature range from 5C to 45C. The 5,000-hour heat cycle test of the modules reveals that the cumulative failure rate after 27 years at 10C is expected to be 0.023%. These first generation LD modules were employed in the transoceanic commercial systems such as Pacific Crossing-1 and the Japan-US cable system projects. We have also succeeded in developing the 980 nm LD for higher output operation with optimizing waveguide design. The 1000 µm long LD showed CW kink-free operation up to 545 mW optical output and a maximum output power of over 650 mW, which was limited by thermal rollover. In addition, a preliminary aging test at 350 mW optical output power at 50C has shown stable operation up to 2,300 h. We also confirmed 300 mW kink-free fiber output power with a co-axial type module with the improved coupling efficiency of approximately 78%. These figures are the highest reported operation levels for 980-nm co-axial type modules.

We propose middleware which works on widely-used commercial off-the-shelf platforms (UDP/IP, FastEthernet, and Windows NT or commercial real-time kernels) to realize real-time distributed services for plant monitoring and control systems. It is not suitable to use TCP/IP for the systems because of its unpredictable re-transmission, while, as well known, UDP/IP does not guarantee certain arrivals of packets and it is also not acceptable for the systems. With UDP/IP, packets are lost mainly because of collisions in a network and buffer overflows. To avoid these packet losses, the middleware controls scheduling of all the packets transmitted between the nodes in a distributed system and prevents excessive collisions and buffer overflows. The middleware provides a necessary set of functions for plant monitoring and control applications. The middleware on each node in a distributed system consists of library functions and run-time modules. An application program on the node is required to use these library functions according to the rules the middleware provides. In this way the middleware can manage all the traffic among the nodes in the system. Receiving requests from the application via library functions, the run-time module of the middleware schedules transmission of messages to other nodes, avoiding unexpected delivery delays or buffer overflows. The module also guarantees application-to-application quality of service (QoS), such as transmission period and delivery deadline, required by the applications. This is achieved by assigning the resources not shared by other services to each distributed service and scheduling these resources so as not to violate the assignment. Here, resources include maximum numbers of packets which a node can receive or send in a specific period (20 msec, for example). We show implementation of the middleware to make it clear how to guarantee application-to-application QoS with some application examples.

This paper proposes a new satellite communication system that enables high-speed communication in a mobile environment. The system configuration combines a terrestrial mobile network and an existing satellite system, and includes a tracking antenna that was newly developed to receive 30 Mbit/s signals from commercial communication satellites. A prototype system comprising the mobile network, the satellite system and a vehicle in which the tracking antenna is installed was constructed for purposes of evaluation and demonstration. A LAN system was incorporated in the experimental vehicle by using the tracking antenna, a satellite router and a Personal Digital Cellular phone. The validity of the proposed system was verified by the tracking antenna driving tests, system UDP tests and FTP throughput tests in a mobile environment.

This paper proposes an adaptive zone selection (AZS) scheme with adaptive modulation for wireless packet transmission systems to achieve high throughput and low delay performances even under non-uniform traffic conditions. In the proposed system, based on the measurement of the propagation path characteristics to each access point (AP) as well as broadcasted blocking probability information from each AP, a terminal autonomously selects an AP and modulation parameters that give the minimum transmission failure probability determined by both the call blocking rate due to lack of radio resource and packet error rate due to severe channel conditions. Computer simulation confirms that the proposed scheme greatly improves throughput and delay performances especially under non-uniform traffic conditions.

In this paper, we describe statistical properties of timing jitter of symbol timing recovery circuit for carrierless amplitude/phase modulation (CAP)-based very high-rate digital subscriber line (VDSL) system. Analytical expressions of the timing jitter for envelope-based timing recovery system, such as squarer-based timing recovery (S-TR) and absolute-value-based timing recovery (A-TR) schemes, are derived in the presence of additive white Gaussian noise (AWGN) or far-end crosstalk (FEXT). In particular, the analytical and simulation results of the timing jitter performance are presented and compared for a 51.84 Mb/s 16-CAP VDSL system. The A-TR system implemented digitally meets the DAVIC's VDSL system requirement, which specifies the maximum peak-to-peak jitter value of 1.5 nsec and the acquisition time of 20 msec.

In any ill-conditioned information-transfer system, as in long-distance communication, we often must construct feedback confirmation channels, in order to confirm that informations received at destinations are correct. Unfortunately, for such systems, undesirable uncertain fluctuations may be induced not only into forward communication channels but also into feedback confirmation channels, and it is such difficult that transmitters always confirm correct communications. In this paper, two fuzzy-set-valued mappings are introduced into both the forward communication channel and the feedback confirmation channel, separately, and overall system-behaviors are discussed from the standpoint of functional analysis, by means of fixed point theorem for a system of generalized equations on fuzzy-set-valued mappings. As a result, a good mathematical condition is successfully obtained, for such information-transfer systems, and fine-textured estimations of solutions are obtained, at arbitrary levels of values of membership functions.

In this paper, we propose a new filesystem named Ad-hoc Filesystem which targets ad-hoc wireless networks. Ad-hoc Filesystem is a serverless filesystem which automatically generates temporary shared space among multiple mobile machines when they gather in a communicable range. The generated space is freely available for participating machines and can be used for any temporary work there. The design of Ad-hoc Filesystem is strongly motivated by the recent wireless network technologies and advances of ad-hoc network techniques. However, targeting such an unstable network forces us a completely different design from existing filesystems. We have designed an initial prototype of Ad-hoc Filesystem and have evaluated the simulation results. Our design is strongly based on an assumption such that people who wish to work together would form a stable group in a range, and replicating data on two different machines would be enough to provide a proper level of availability. Hence, Ad-hoc Filesystem distributes files among multiple machines and duplicates them, in order to keep the files available even if some of participating machines arbitrarily leave the communication range. The directory entries are kept as a soft-state mechanism maintained by exchanging broadcast packets. The simulation results show that using broadcast to maintain system state hardly affects the overall system performance, and optimizations such that delaying replies with broadcast and sensing other packets promiscuously during the delay reduce the overhead significantly. Also the result indicates that our strategy that keeps two replicas for each data is promising to provide availability. Although further investigation based on real implementation remains important work, we believe that the prototype has a contribution to realize the possibility of ad-hoc filesystem by synthesizing number of previous works in areas such as network filesystems, server replication and ad-hoc wireless networks.

This paper proposes a very small on-chip multimedia real-time OS for embedded system LSIs, and demonstrates its usefulness on MPEG-2 multimedia applications. The real-time OS, which has a conditional cyclic task with suspend and resume for interacting hardware (HW) / software (SW) of embedded system LSIs, implements the minimum set of task, interrupt, and semaphore managements on the basis of an analysis of embedded software requirements. It requires only about 2.5 Kbytes memory on run-time, reduces redundant conventional cyclic task execution steps to about 1/2 for HW/SW interactions, and provides sufficient performance in real-time through implementing two typical embedded softwares for practical multimedia system LSIs: an MPEG-2 system protocol LSI and an MPEG-2 video encoder LSI. This on-chip multimedia real-time OS with 2.5 Kbyte memory will be acceptable for future multimedia embedded system LSIs.

We propose a new conditional linearization based on left-right separated conditional term rewriting systems, in which the left-hand side and the right-hand side of a rewrite rule have separate variables. By developing a concept of weight decreasing joinability we first present a sufficient condition for the Church-Rosser property of left-right separated conditional term rewriting systems. Applying this result to conditional linearization, we next show sufficient conditions for the unique normal form property and the Church-Rosser property of non-duplicating (unconditional) term rewriting systems even if they are non-left-linear or overlapping.

Understanding traffic characteristics in mobile communications is invaluable for planning, designing, and operating cellular networks, and various mobility models have therefore come to be developed to predict traffic characteristics. In this paper, cell-dwell-time distribution and transition probability in a virtual cellular system are first estimated from the results of measuring taxi motion using the Global Positioning System (GPS) for large-city and small-city ranges of motion. Then, on the basis of simulations using these estimations, traffic characteristics like handoff rate and channel blocking probability in a cellular system are evaluated. It was found that a difference between large and small cities could be observed in speed distribution and direction-of-travel probability, but only a slight difference in cell-dwell-time distribution.

FDMA/TDMA non-geostationary earth orbit satellite systems (Non-GEOS) generally require a pre-planned pool of radio resource, i.e., frequency and time slot plan (FTSP), for each gateway earth station (GES) prior to the real-time channel assignment by the multiple GES's sharing the resources harmoniously. The time-variant nature of those systems implies that a dynamic FTSP planning method is crucial to the operation to cope with the time-variant traffic demand and the inter-beam interference condition. This paper proposes and compares three algorithms (Serial-numbering, DP-based, and Greedy algorithms) mixed with two strategies (concentrated- and spread-types) for the resource allocation. The numerical evaluation demonstrates that Greedy algorithm with the spread-type strategy is very effective and promising with feasible calculation time for the FTSP generation.