Although all-optical gate switches based on the intersubband absorption in nitride quantum wells are predicted to operate at 1 Tb/s, realization of strong intersubband absorption at the optical communication wavelength is still difficult. An alternative approach is an interferometer-type gate switch utilizing refractive index change due to the intersubband absorption of a control pulse at a longer wavelength. Feasibility of Mach-Zehnder interferometer (MZI) gate switches, in which 1.55-µm pulses are controlled by 1.85-µm pulses, was theoretically investigated by finite-difference time-domain (FDTD) simulator. Although the effective phase shift does not reach π, 22.5% of the signal pulse energy was predicted to be gated by a 10-pJ control pulse in the MZI switch. Even 1.3-µm pulses can be controlled by 1.85-µm pulses at the expense of the switching energy. This approach provides a way to process signal pulses at the optical communication wavelength utilizing strong intersubband absorption at a longer wavelength.

A fully on-chip open-drain CMOS output driver was designed for high bandwidth DRAMs, such that its output voltage swing was insensitive to the variations of temperature and supply voltage. An auto refresh signal was used to update the contents of the current control register, which determined the transistors to be turned-on among the six binary-weighted transistors of an output driver. Because the auto refresh signal is available in DRAM chips, the output driver of this work does not require any external signals to update the current control register. During the time interval while the update is in progress, a negative feedback loop is formed to maintain the low level output voltage (VOL) to be equal to the reference voltage (VOL.ref) which is generated by a low-voltage bandgap reference circuit. Test results showed the successful operation at the data rate up to 1 Gb/s. The worst-case variations of VOL.ref and VOL of the proposed output driver were measured to be 2.5% and 7.5% respectively within a temperature range of 20 to 90 and a supply voltage range of 2.25 V to 2.75 V, while the worst-case variation of VOL of the conventional output driver was measured to be 24% within the same ranges of temperature and supply voltage.

In this paper we addresses the problem of finding feasible solutions for the Group Multicast Routing Problem (GMRP). This problem is a generalization of the multicast routing problem whereby every member of the group is allowed to multicast messages to other members from the same group. The routing problem involves the construction of a set of low cost multicast trees with bandwidth requirements for all the group members in the network. We first prove that the problem of finding feasible solutions to GMRP is NP-complete. Following that we propose a new heuristic algorithm for constructing feasible solutions for GMRP. Simulation results show that our proposed algorithm is able to achieve good performance in terms of its ability of finding feasible solutions whenever one exist.

In this paper, we present several unitary transform-domain filtering techniques based on Karhaunen-Loeve Transform (KLT) for narrow-band interference rejection in CDMA communication systems. The reason for selecting the KLT is that it is an optimum unitary transform in the sense of packing the energy of the narrow-band interference. As a result after applying this transform, a small portion of the transformed signal would be interfered by the narrow-band interference, and thus must be set to zero. Due to unavailability of the optimum transform (KLT), several sub-optimum transforms are presented and their performances are compared with the well-known conventional transform methods such as Discrete Fourier Transform (DFT) and Discrete Cosine Transform (DCT) in the presence of both Auto Regressive (AR) and sinusoidal narrow-band interference. Our simulation results show that the proposed transform methods significantly outperform the conventional methods.

Grouping multiple voice frames into a single IP packet ("frame grouping") is a commonly mentioned approach to saving bandwidth in IP telephony. But little is known as to when, how, and how much frame grouping should be done in Internet environment. This paper explores the feasibility and the methods of frame grouping based on Internet delay measurement. Specifically, we propose an adaptive frame grouping method that minimizes the delay violation while reducing the bandwidth usage by as much as a factor of two under real Internet delay fluctuations. The performance of the method is evaluated as it is used against a single voice stream and then against multiple voice streams.

We investigate the engineering of the impurity bands in photonic crystals (PCs) for realizing high-efficiency wave guiding, all-optical switching and optical delay for ultrashort optical pulses. It is found that quasi-flat impurity bands suitable for the transmission of ultrashort pulses can be achieved by properly controlling the configuration of coupled cavity waveguides (CCWs). At sharp corners, high bending efficiency is obtained over the entire impurity band. All-optical switching can be realized by creating a dynamical band gap at the center of an impurity band. The concentration of electromagnetic wave at defect regions leads to high switching efficiency while the tunable feature of PC defects makes all-optical control possible. It is also revealed that CCWs with quasi-flat impurity bands provide efficient group delay for ultrashort pulses with negligible attenuation and distortion. From the viewpoint of practical fabrication, the effect of disorder on the transmission property of impurity bands is discussed and the criterion for localization transition is determined.

Phase-based methods for estimating the frequency of a sinusoid have typically suffered from a threshold effect, where for signal to noise ratio (SNR) below the threshold, the mean squared error of the estimate rapidly increases. Furthermore, it is a significant problem that the threshold is considerably high and strongly depends on frequency. To overcome the difficulties, a Kalman-based sinusoidal estimator bank (KSEB) is proposed. In the derivation of the KSEB, a four-channel filter bank and decimation technique are effectively used. The computer simulation also demonstrates the superiority of the KSEB to the other frequency estimators.

Recently, demand on class-of-service (CoS) has known a great increase thanks to a set of real-time applications such as Internet Telephony service. Class-Based Queuing (CBQ) is considered as an efficient queuing mechanism to guarantee CoS. ALTQ is a widely used platform for realizing CBQ. In this paper, we verify through experiments that bandwidth control of CBQ/ALTQ contains overhead for fluctuating traffic. To avoid such an overhead, we introduce dynamic bandwidth allocation scheme for real-time traffic fluctuating within fixed ranges. In the light of the limited network resources, it quickly becomes obvious that when the traffic rate exceeds the maximum available bandwidth, arriving packets will be accumulated in the router queue. As a result, the traffic delay increases and the quality of real-time applications is degraded. To cope with such a problem, we revise the RED algorithm for a large amount of traffic and propose a new packet discard algorithm that uses bandwidth as a trigger. Experiment results show that our proposal outperforms the already existing packet discard algorithms (RED, DropTail) in providing lower delay/jitter services. We show the efficiency of our proposal using a real system.

Transmission and distribution systems are investigated for application in future fiber optic super-broadband and super-multi-channel subscriber loops. Gradual upgrading is considered so that future systems can keep compatibility with existing systems. First, time frame and strategies for subscriber loop upgrade are overviewed and assumptions for evolution of broadband multimedia distribution systems are discussed. It is suggested that upgrading to super-high definition (SHD) quality multimedia is desirable. Next, some examples of extra-auxiliary picture (EAP) formats are discussed to show the possibility of improving upgradability and compatibility by using extra-channels. Then multiplexing and channel selecting systems are investigated for economical realization of super-multi-channel distribution and flexible channel selection, and hybrid multiplexing (HMUX) and a trans-selector (T-SEL) are proposed. Finally, the efficiencies of HMUX and T-SEL are discussed by using numerical examples. Although broadband down streams are mainly considered, other streams such as IP traffics can be accommodated in the distribution systems investigated in this paper.

Surging capacity demand triggered by the increasingly mobile-oriented and exponentially growing Internet has accelerated convergence of networking technologies. In the core network side, IP and photonics have been the two key driving factors of technical innovations. Amid this technical turmoil, Generalized MPLS (GMPLS) in IETF has recently attracted sizable attentions, as it offers potential for "Grand Unification Theory" for network technology convergence. Despite its prospects, however, the proposal is still missing comparable structures in management plane, which is in dire need for carrier-class, reliable operations. Among many industry proposals and standards, TINA vision on connection management architecture (CMA) is the one offering practical and deployable architecture for the converged photonic IP network. TINA IP Control and Management (IPCM) WG was established during TINA phase II (1998-2000), to study IP control and management issues using the architecture basis of TINA-CMA. Latest activities in TINA IPCM WG, compiling experience at Sprint, Telia, Telecom Italia Lab., and Fujitsu, have resulted in a specification for connectivity provider reference points, namely ConS, ConC, and FCon. Use of TINA CMA as building blocks for the IP photonic network convergence is illustrated. An overview of a ConS reference point specification for managed IP connectivity service, named ConS-IPCM, is explained.

The VHF broadband radio interferometry operated from 25 MHz to 250 MHz has been developed for observing lightning discharge progression. The lightning images are derived by sensing the electromagnetic-waves which are radiated during the discharges. The perpendicular baseline geometry provides the angular locations (azimuth and elevation) of lightning radiation sources. The lightning observations have been conducted in the Hokuriku District in 1999. The station consisted of three broadband antennas and an electric field antenna as well as a GPS receiver. The system was able to reconstruct lightning discharge channels in two-spatial dimensions and in time sequence. As one of the observation results, an upward negative cloud-to-ground lightning flash will be presented.

In this paper, the statistical characteristics of rain attenuation in the equatorial zone are investigated. A more reasonable LMS channel model incorporating weather impairments is proposed and compared to the weather-affected Ka-band land mobile satellite (LMS) channel model suggested by Loo. The proposed LMS model uses Lutz's LMS channel model as its basis. The PDF of the received signal and BER performance derived from Loo's model and the proposed channel model are quantified and compared to verify the effectiveness of the proposed model. Finally, the influence of weather impairments on the BER performance is evaluated under various weather conditions, which clearly shows the superiority of the proposed model.

In this paper, we present a design for an optical video transmission system employing a super wide-band FM modulation scheme. We focus on the design of optical transmitters and receivers, especially a wide-band electrical-to-optical converter and optical-to-electrical converter. With this system, it is important to develop optical and microwave devices which have a wide frequency response combined with flat group delay characteristics in order to improve the quality of the video signals after transmission. We also analyze theoretically the hybrid transmission capacity of AM analog video signals and 64QAM signals for digital video and data, and show the FM modulation parameters needed to realize high quality transmission. An experimental evaluation shows that our designed optical transmitter and receiver achieve high quality for the various channel plans for AM/64QAM hybrid transmission. The system has high received optical sensitivity and a wide optical dynamic range, allowing it to distribute analog video, digital video, and Internet data to many users over a wide area.

This paper proposes a non-linear adaptive algorithm, the amplitude banded RLS (ABRLS) algorithm, as an adaptation procedure for time variant channel equalizers. In the ABRLS algorithm, a coefficient matrix is updated based on the amplitude level of the received sequence. To enhance the capability of tracking for the ABRLS algorithm, a parallel adaptation scheme is utilized which involves the structures of decision feedback equalizer (DFE). Computer simulations demonstrate that the novel ABRLS based equalizer provides a significant improvement relative to the conventional RLS DFE on a rapidly time variant communication channel.

The IETF Differentiated Services (DiffServ) framework achieves scalability by (1) aggregating traffic flows with coarse grain QoS on the data plane, and (2) allocating network resources with a bandwidth broker (BB) on the control plane. However, there are many issues that need to be addressed under such framework. First, it has been shown that the concatenation of strict priority (SP) scheduler of class-based queues (CBQ) can cause delay jitter unbounded under certain utilization, which is not acceptable to support the premium service (PS). Furthermore, it is not clear how such a DiffServ network can support traffic flows requiring the guaranteed service (GS), which is a desirable feature of the future Internet. This paper presents architecture and mechanisms to support multiple QoS under the DiffServ paradigm. On the data plane, we present a node architecture based on the virtual time reference system (VTRS). The key building block of our node architecture is the core-stateless virtual clock (CSVC) scheduling algorithm, which, in terms of providing delay guarantee, has the same expressive power as a stateful weighted fair queueing (WFQ) scheduler. With the CSVC scheduler as our building block, we design a node architecture that is capable of supporting integrated transport of the GS, the PS, the assured service (AS), and the traditional best effort (BE) service. On the control plane, we present a BB architecture to provide flexible resource allocation and QoS provisioning. Simulation results demonstrate that our architecture and mechanisms can provide scalable and flexible transport of integrated traffic of the GS, the PS, the AS, and the BE services.

Rectangular/circular-to-radial waveguide tra-nsformers through a ring slot have been proposed for the feeder of radial line slot antennas (RLSAs) in millimeter wave application. Rotating electric modes are excited by a set of ring slot and perturbation dog bone slot. Basic operation is observed in 12 GHz band. Concentric array radial line slot antennas fed by these transformers are fabricated and the antenna gain of 26.9 dBi with the efficiency more than 60% is measured. The applicability for millimeter wave is verified for 38 GHz band RLSA fed by the rectangular waveguide. The measured gain of the antenna is 22.5 dBi with the efficiency of 53% with the diameter of 46mm and 26.4 dBi with 61% with the diameter of 66mm.

The authors have developed V-band high electron mobility transistor (HEMT) MMICs adopting benzo-cyclo-butene (BCB) thin-film layers on GaAs substrates. Since the BCB thin-film layers, which can change the thickness of arbitrary parts on a circuit, are used for these MMICs, both a thin-film microstrip (TFMS) line, offering the advantages of great flexibility in layout and small size, and a coplanar waveguide (CPW), offering the advantage of low loss, can be used according to the purpose of the MMIC. Here we introduce the four types of V-band MMICs that we fabricated: low noise amplifier (LNA), mixer, voltage controlled oscillator (VCO), and power amplifier (PA). The optimum transmission lines were chosen from the TFMS line and the CPW for these MMICs. Miniaturization of the LNA MMIC and the mixer MMIC were attained by adopting the TFMS line, whereas adoption of the CPW enabled the VCO MMIC to achieve high performance. These results indicate that it is important to choose the optimum transmission line according to the purpose of the circuit function for each MMIC. It was confirmed that these newly developed MMICs using the BCB thin-film dielectric layers are attractive for millimeter-wave applications.

Using a point matching method, we have numerically analyzed resonance frequencies and unloaded Q factor of whispering gallery modes in a millimeter wave region that are well known as an intrinsic mode of a dielectric disk resonator. We express field distributions of the resonance modes by a summation of spherical waves. Tangential electromagnetic fields inside the disk are matched to those outside the disk at appropriate matching points on a boundary. As the result, a 4N 4N (N; number of matching points) determinant is derived as an eigenvalue equation of the disk resonator. Since elements of the determinant are complex numbers, a complex angular frequency is introduced to make a value of the determinant zero. For a location of the matching points, we also introduce a new technique which is derived from a field expression of the whispering gallery modes. Since an azimuthal angle dependence of the field distributions with a resonance mode number m is presented by the associated Legendre function Pnm(cos θ), we define abscissas θi of the matching points as solutions of Pm+2N-1m (cos θ) = 0. Considering the field symmetry, we also modify the eigenvalue equation to a new eigenvalue equation which is expressed (4N - 2) (4N - 2) determinant. From the results of our numerical analysis, we can find that the resonance frequencies and unloaded Q factor well converge for number of matching points N. A comparison of numerical results and experimental ones, in a millimeter wave band (50 - 100 GHz), shows a good agreement with each other. It is found that our analysis is effective for practical use in the same wave band.

Power supply rejection ratio (PSRR) characteristics of a switched capacitor filter (SCF) is improved when using an equal level diagram design of a leapfrog type filter. By using this design method, it is shown that PSRR of a SCF measured is improved about 20 dB.

A method is described that can allocate bandwidth to each user flow fairly in a scalable network architecture such as differentiated services architecture. As promising queueing techniques for providing differentiated services, class-based packet scheduling and selective packet discarding have been attracting attention. However, if we consider that bandwidth should be allocated to each flow in a weighted manner, the parameters used in these methods such as the weight assigned to each class queue should be pre-determined appropriately based on an assumption about the number of flows in each class. Thus, when the actual traffic pattern differs from the assumed one, they may not work well. Instead of assuming the traffic conditions, our method estimates the number of active flows in each class by simple traffic measurement and dynamically changes the weight assigned to each class queue based on the estimated number. Our method does not need to maintain the per-flow state, which gives it scalability. Simulation showed that this method is effective under various patterns of the number of active flows.