The Bluetooth system provides point-to-point or point-to-multipoint communications with no peer-to-peer communication. For peer-to-peer communication, a slave should be able to communicate with other slaves as well as a master. To do this, the master should indirectly forward the packets. However, the end-to-end delay of forwarding packets may be increased because the packets should be forwarded at network layer. Forwarding packets for peer-to-peer communications may also bring about some needless waste of wireless resource. In this paper, we propose the addressing policy for efficient peer-to-peer communications in Bluetooth. We also address the dynamic master selection policy in which a master is dynamically selected in order to minimize the average channel occupancy. To dynamically change master in a piconet, the master-slave switching should be executed as soon as possible. Therefore, we propose the fast master-slave switching mechanism in order to minimize the switching delay. It is observed from the simulations that our proposed policies perform better than the naive Bluetooth specification.

As new applications of THz waves emerge, new active and passive components need to be developed. The efficiency of wave guiding systems can be significantly increased with the use of MEMS approaches as well as with the development of new planar antenna concepts with high bunching properties. Generation of sufficient THz power relies on new active devices like Heterostructure Barrier Varactors and cascaded quantum structures, but also in the optimisation of new generation concepts. One of these is photomixing in non-linear materials with very short carrier lifetimes, like low-temperature-grown GaAs.

This paper describes an experimental study on resonant properties of the plasma-wave field-effect transistors (PW-FET's). The PW-FET is a new type of the electron devices, which utilizes the plasma resonance effect of highly dense two-dimensional conduction electrons in the FET channel. Frequency tunability of plasma-wave resonance in the terahertz range was experimentally investigated for sub 100-nm gate-length GaAs MESFET's by means of laser-photo-mixing terahertz excitation. The measured results, including the first observation of the third-harmonic resonance in the terahertz range, however, fairly deviate from the ideal characteristics expected for an ideal 2-D confined electron systems. The steady-state electronic charge distribution in the MESFET channel under laser illumination was analyzed to study the effect of insufficient carrier confinement on the frequency tunability. The simulated results support the measured results. It was clarified that an ideal heterostructure 2-D electron confinement is essential to assuring smooth, monotonic frequency tunability of plasma-wave resonance.

In this paper, we focus on the problem of secure multicast in dynamic groups. In this problem, a group of users communicate using a shared group key. Due to the dynamic nature of these groups, to preserve secrecy, it is necessary to change the group key whenever the group membership changes. While the group key is being changed, the group communication needs to be interrupted until the rekeying is complete. This interruption is especially necessary if the rekeying is done because a user has left (or is removed). We split the rekeying cost into two parts: the cost of the critical path--where each user receives the new group key, and the cost of the non-critical path--where each user receives any other keys that it needs to obtain. We present a family of algorithms that show the tradeoff between the cost of the critical path and the cost of the non-critical path. Our solutions allow the group controller to choose the appropriate algorithm for key distribution by considering the requirements on critical and non-critical cost. In our solutions, the group controller can dynamically change the algorithm for key distribution to adapt to changing application requirements. Moreover, we argue that our solutions allow the group controller to effectively manage heterogeneous groups where users have different requirements/capabilities.

This paper investigates the use of chaotic pulsewidth modulation (CPWM) scheme for electronic ballasts to eliminate visible striations (appearance of black and white bands along the lamp tube) in fluorescent lamps. As striations can be eliminated by superimposing a small amount of dc current or low frequency ac current to the electrodes to produce composite current waveform through the lamp, the underlying principle of this work is based on the fact that the power spectral density of the lamp current will be rich of low-frequency harmonics at the output of inverters switching with CPWM. Most importantly, the lamp life will not be affected with chaotic switchings, because the lamp current crest factor is found to be similar to the one with standard pulsewidth modulation (PWM) and the lamp current does not have dc component. The effectiveness of eliminating striations is confirmed experimentally with a T8 36W prototype.

A new type of compact one dimension (1-D) microstrip photonic bandgap (PBG) structure for filter is presented. A miniature semiconductor-based structure band-stop filter with four cells is simulated, fabricated, and measured. Agreement between the experimental and simulation results has been achieved. The filter with four proposed PBG structure exhibits deep (about -60 dB) and steep (about 40 dB/GHz) stop-band characteristics. It also has less loss and ripples in the pass-band. The period of the PBG lattice is about 0.2 λe (λe, guiding wavelength at the center frequency of stop-band), or 0.068 λ0 (λ0 wavelength in air), and the filter is very compact and much easier for fabrication and realization in MIC and MMIC.

In this paper we present a new, two-centered electronic voting scheme that is capable of preserving privacy, universal verifiability, and robustness. An interesting property of our scheme is the use of double encryption with additive homomorphic encryption functions. In the two-centered scheme, the first center decrypts the ballots, checks the eligibility of the voters, and multiplies each eligible vote, which is still encrypted in the cryptosystem of the second center. After the deadline is reached, the second center obtains the final tally by decrypting the accumulated votes. As such, both centers cannot know the content of any individual vote, as each vote is hidden in the accumulated result, therefore the privacy of the voters is preserved. Our protocols, together with some existing protocols, allow everyone to verify that all valid votes are correctly counted. We apply the r-th residue cryptosystem as the homomorphic encryption function. Although decryption in the r-th residue cryptosystem requires an exhaustive search for all possible values, based on experiments we show that it is possible to achieve desirable performance for large-scale elections.

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.

In generating Frequency-Hopping (FH) sequences for Frequency Hopping Spread Spectrum Multiple Access (FH-SSMA) applications, binary maximal-length sequences (m-sequences) over GF(2m) have been preferred because of their characteristics of good Hamming correlation property, long period capability and high speed generation in association with simple hardware implementation based on Feedback Shift Registers (FSR). In practice, however, one difficulty of applying such sequences into the FH-SSMA communication systems with a wide bandwidth such as Military Satellite Communication (MilSatCom) is that the number of hopping frequency slots available may be far from a power of 2 in proportion to the spreading bandwidth. In that case, we can not make good use of the spreading bandwidth. In this paper, we propose a construction of some favorable FH sequences which deals effectively with the above difficulty using FSR and some nonlinear logic by introducing a re-mapping method. We show that the resulting sequences satisfy the (almost) uniform symbol distribution in one period and preserve a reasonably good Hamming correlation property so that they are appropriate for FH-SSMA applications.

A shared-TDD scheme has been proposed for accommodation of asymmetric communications between uplink and downlink traffic. The application of shared-TDD scheme to CDMA cellular systems causes inter-link interference because CDMA cellular systems use the same frequency band for all cells. This paper proposes a transmission control scheme for uplink packets to relieve the effect of inter-link interference in CDMA/shared-TDD cellular packet systems. In the proposed scheme, mobile stations select transmission slots based on their location and the status of slot allocations in own and the adjacent cells. Computer simulations show that the proposed scheme relieves the effect of inter-link interference, and thus improves the downlink transmission efficiency.

A Distributed Computing System (DCS) contributes in proper partitioning of the tasks into modules and allocating them to various nodes so as to enable parallel execution of their modules by individual different processing nodes of the system. The scheduling of various modules on particular processing nodes may be preceded by appropriate allocation of modules of the different tasks to various processing nodes and then only the appropriate execution characteristic can be obtained. A number of algorithms have been proposed for allocation of tasks in a DCS. Most of the solutions proposed had simplifying assumptions. The very first assumption has been: consideration of a single task with their corresponding modules only; second, no consideration of the status of processing nodes in terms of the previously allocated modules of various tasks and third, the capacity and capability of the processing nodes. This work proposes algorithms for a realistic situation wherein multiple tasks with their modules compete for execution on a DCS dynamically considering their architectural capability. In this work, we propose two algorithms based on the two well-known A* and GA for the task allocation models. The paper explains the algorithms elaborately by illustrated examples and presents a comparative performance study among our algorithms and the algorithms for task allocation proposed in the various literatures. The results demonstrate that our GA based task allocation algorithm achieves better performance compared with the other algorithms.

Within a few years it will be possible to integrate a billion transistors on a single chip operating at frequency more than 10 GHz. At this integration level, we propose using a multi-level ISA to express fine-grain data parallelism to hardware instead of using a huge transistor budget to dynamically extract it. Since the fundamental data structures for a wide variety of data parallel applications are scalar, vector, and matrix, our proposed Trident processor extends a scalar ISA with vector and matrix instruction sets to effectively process matrix formulated applications. Like vector architectures, the Trident processor consists of a set of parallel lanes (each lane contains a set of vector pipelines and a slice of register file) combined with a fast scalar core. However, Trident processor can effectively process on the parallel lanes not only vector but also matrix data. One key point of our architecture is the local communication within and across lanes to overcome the limitations of the future VLSI technology. Another key point is the effective execution of a mixture of scalar, vector, and matrix operations. This paper describes the architecture of the Trident processor and evaluates its performance on BLAS and on the standard matrix bidiagonalization algorithm. The last one is evaluated as an example of an entire application based on a mixture of scalar, vector, and matrix operations. Our results show that many data parallel applications, such as scientific, engineering, multimedia, etc., can be speeded up on the Trident processor. Besides, the scalability of the Trident processor does not require more fetch, decode, or issue bandwidth, but requires only replication of parallel lanes.

It is shown that bounded impulse action can be combined with usual bang-bang control input to minimize the performance index. Especially for unstable oscillators, the size of controllable region can be increased. We present results on how to minimize the performance index using both ordinary bang-bang control and impulse actions with a recharge constraint on impulse firing. Following the maximum principle and necessary conditions induced from usual perturbation arguments, the mixed control input (bang-bang and impulse actions) is represented in adjoint state and then state variable feedback form. Simulation results show how the switch curves can be used to determine the optimal control value.

Power Line Communication (PLC) is very attractive for achieving high-rate in-home networks. Noise in power lines is modeled as a cyclostationary Gaussian process. In order to achieve reliable communication using power lines, effective measures including error control techniques need to be taken against this particular noise. This paper focuses its attention on an effect of turbo codes on PLC. We adopt two noise environments for examining the effect in terms of BER performance. The result of the examination provides that turbo codes have enough capability to limit the effect of the noise. It also provides that the effect depends on size of a channel interleaver. Since an effective SNR estimation scheme should be required to apply turbo codes to PLC, we also examine the effect of two SNR estimation schemes in terms of BER performance.

In this paper, we first address the current state of broadband services in Korea. Here, we introduce relevant statistics, current access network architectures, and activities of some major carriers. We also briefly introduce Korean government's policies on research and development projects and plans for promoting the country toward an advanced information society. We then introduce a large-scale, collaborative project named "Photonic Access To the Home (PATH)" with five-year period of performance, started in year 2002. The project is under leadership of the government and ETRI in collaboration with universities and industry. We finally provide a rather detailed description of the FTTH (Fiber To The Home) technology based on the wavelength division multiplexing technology, which has been under research in our laboratory as a part of the PATH project. We show some of our achievement including new architectures and networking principles for the FTTH network, analysis of the dynamic allocation of user bandwidth, and the experiment for a low-cost WDM optical source.

Implementation issues on generalized multi-protocol label switching (GMPLS) -based photonic switching networks are experimentally analyzed. A resilient control plane architecture using in-fiber and out-of-fiber control channels is proposed to resolve issues of establishing the control plane in out-of-band networks. The resilient control plane is demonstrated in a photonic cross-connect (PXC) -based GMPLS network involving a 1,000 km transmission line. Fast signaling for provisioning and restoration operation is accomplished by implementing in-fiber control channels as primary, and the out-of-fiber control channels effectively operate as secondary and restore messaging of the control information between neighbors. The control channel protection is initiated by the link management protocol (LMP). Using the test bed, optical layer routing operation is investigated to assess the effects on the signal quality of wavelength paths, and transparent routing of the wavelength paths over one-hop and two-hops route is demonstrated within 1 dB difference regarding the Q factor. Stable operation of loss of light (LOL) -triggered restoration is demonstrated by setting the optical level threshold 5 dB higher than the amplified spontaneous emission (ASE) noise level.

Microstrip antennas on various Uniplane Compact Photonic BandGap (UC-PBG) substrates are investigated. Particularly, anisotropic characteristics of UC-PBG is studied and applied to the design of microstrip diplexer antennas. Moreover, an Embedded UC-PBG (EUC-PBG) scheme is presented to overcome the strong backward radiation caused by the conventional UC-PBG antennas. Such antennas demonstrate the improved radiation properties over the conventional UC-PBG antennas, and the evidence on surface wave suppression is also demonstrated. Experimental results show very good agreement with theoretical predictions.

Recently, diverse multimedia applications with stringent multiple Quality of Service (QoS) requirements have been increasing. In particular, multicast communication has become more popular because of its availability and for efficient use of network resources. Most multicasts are point-to-multipoint, in which a source delivers data to multiple designated recipients, such as for video or audio distribution. In the near future, multipoint-to-multipoint communication services, including multimedia collaborations such as video conferencing and distant-learning, will be developed. However, when a conventional multicast routing algorithm is applied to a multipoint-to-multipoint communication service, it might result in excessive traffic concentration on some links. Therefore, we propose a new multipoint-to-multipoint routing method. It utilizes the Fallback+ algorithm to perform multicast routing for the purpose of satisfying multiple QoS requirements and alleviating traffic concentrations. Simulation experiments show that our method improves traffic load balance and achieves efficient use of network resources.

An IP (Internet Protocol) over WDM network is expected to be an infrastructure for the next-generation Internet by directly carrying IP packets on the WDM-based network. Among several architectures for IP over WDM networks, one promising way is to overlay a logical topology consisting of lightpaths over the physical WDM network so that IP packets are carried on the lightpaths. The conventional methods for designing the logical topology have been focusing on maximizing throughput of the traffic. However, when the WDM network is applied to IP, the end-to-end path provided by the logical topology of the WDM network is not suitable to IP since IP has its own metrics for route selection. In this paper, we propose a new heuristic algorithm to design a logical topology by considering the delay between nodes as an objective metric. This algorithm uses a non-bifurcated flow deviation to obtain a set of routes that IP packets are expected to traverse. Our proposal is then compared with conventional methods in terms of the average packet delays and throughput. It is shown that our method becomes effective when the number of wavelengths is a limited resource.

We present a design and implementation of a QoS control mechanism in an Adaptive Multimedia Communication System (AMCS) using multiagent-based computing technology. In this paper, we first define functional requirements for AMCS. Subsequently we describe the design and implementation of AMCS with a knowledge-based multiagent framework to fulfill the functional requirements. Moreover we evaluate the adaptability of the prototype systems of AMCS with the operational situations observed in its experiments. From the result of the experiments, we conclude that the multiagent-based design and implementation is reasonable for construction of AMCS.