This paper proposes a credit-based congestion control scheme for multicast communication which employs application-specific processing at intermediate network nodes. The control scheme was designed not only to take advantage of credit-based flow control for unicast communication, but also to achieve flexibility supported by active network technology. The resultant active multicast congestion control scheme is able to meet the different requirements of various multicast applications in terms of reliability and end-to-end latency. The performance of the proposed control scheme was evaluated using both discrete-event simulations and experiments on a prototype active network implementation. The results show that the proposed scheme performs very well in terms of fairness, responsiveness, and scalability. The implementation experiences also confirmed the feasibility of the scheme in practice.

In this article we present the subject of wideband channel modeling and simulation, stressing the method of orthogonalization. We compare the performance of this simulation method using Karhunen-Loeve, Wavelets and other basis over radio channels represented via the Input-Delay Spread Bello Function.

The electronically steerable passive array radiator (ESPAR) antenna performs analog aerial beamforming that has only a single-port output and none of the signals on its passive elements can be observed. This fact and one that is more important--the highly nonlinear dependence of the output of the antenna from adjustable reactances--makes the problem substantially new and not resolvable by means of conventional adaptive array beamforming techniques. A novel approach based on stochastic approximation theory is proposed for the adaptive beamforming of the ESPAR antenna as a nonlinear spatial filter by variable parameters, thus forming both beam and nulls. Our theoretic study, simulation results and performance analysis show that the ESPAR antenna can be controlled effectively, has strong potential for use in mobile terminals and seems to be very perspective.

It is of considerable interest to study the vortex behavior of a multiply connected superconductor for potential applications of vortex devices. Our sample is made of a type-I superconductor Pb and a capillary plate. The nominal sizes are 1-µm in hole diameter and 1.8-µm in lattice pitch. The microholes form triangular lattice while a superconducting network consists of a honeycomb lattice. When each hole accommodates a single vortex 0, an applied magnetic field becomes a nominal matching field (7.83 G). We measure the magnetization curve of sample by means of a SQUID (superconducting quantum interference device) magnetometer in the accurate small fields on the order of Gauss. We find a sharp magnetization peak at 8.2 G at temperatures near the critical temperature Tc.

The measurement sensitivity of microwave surface resistance, Rs, of high temperature superconducting (HTS) thin films using half-wavelength microstrip resonator with copper and HTS ground plane is analyzed for fundamental and higher order modes of the resonator. The estimated sensitivity of Rs-measurement is at least an order of magnitude greater at fundamental resonant frequency compared to when measured using higher order harmonic modes.

We have fabricated ramp-type Josephson junctions in trilayer structures. A bilayer of YBa2Cu3O7-x (YBCO)/CeO2 was deposited on a SrTiO3 (100) substrate. Then, circle patterns with a diameter of 2 µm were etched on the bilayer surface using standard photolithography process. During the Ar ion milling with an incident angle of 45 degrees to the bilayer surface, the sample was rotated. This process led to upside-down conical formations. After the ramp-edge surface was modified, another YBCO film was deposited for the top electrode. The junctions showed the I-V characteristics between resistively shunted junction and flux-flow types.

Iterative schemes for demodulating M-ary orthogonal signaling formats in direct-sequence code-division multiple access (DS-CDMA) systems are proposed and compared with the standard noncoherent matched filter receiver. Interference cancellation, i.e., (approximative) removal of the multiple access interference (MAI) by means of subtraction is studied. The considered system is similar to the uplink (reverse link) of an IS-95 system. Hence, the received signals from the concurrent users are asynchronous, and no pilot signals are available for channel estimation. A decision-directed algorithm is proposed for estimating the time-varying complex channel gains of a multipath channel. The receivers are evaluated on Rayleigh-fading channels and are shown to provide large capacity gains compared with the conventional receiver.

This paper proposes a maneuvering target tracking algorithm using multiple model filters. This filtering algorithm is discussed in terms of tracking performance, tracking success rate and tracking accuracies for short sampling interval as compared with other conventional methodology. Through several simulations, validity of this algorithm has been confirmed.

This article addresses the problem of designing and implementing multigigabit post-detection filters for application in optical communication systems using optical soliton pulses. The designed filters have the main advantages of full integration, electrically adjustable frequency response and active input and output impedance match.

A new low-voltage, all-in-one ESD (electrostatic discharging) protection circuit was designed. One such ESD protection unit is enough to protect each I/O pad against ESD stresses of all modes, i.e., from I/O to power supply and ground positively and negatively. This novel ESD circuit features adjustable trigger-voltage, i.e., 5 V to 60 V, with low turn-on threshold down to 5 V, symmetric active discharging channels in all directions, fast response time of 0.1 to 0.3 ns, and high ESD performance/area ratio of greater than 80 V per micrometer width. It was implemented in commercial BiCMOS technologies and achieved 14 kV human body model (HBM) and 15 kV air-gap IEC ESD protection levels. This compact ESD structure can not only provide adequate ESD protection, but also minimize the ESD-induced parasitic effects, which makes it a suitable ESD protection solution for mixed-signal and RF ICs in very deep sub-micron regime.

In this paper, we discuss an IF image rejection system with variable bandwidth and center frequency. The system is consists of a pair of frequency mixers multiplied by the complex sinusoid and a complex analog filter. By employing the complex leapfrog structure using OTA-C configuration and the frequency transformation from the normalized LPF, the proposed system is capable of variable bandwidth and center frequency characteristics. SPICE simulations result more than 43 [dB] image rejection is achieved for 6 [kHz] and 12 [kHz] bandwidths at 50 [kHz] IF.

We consider to design approximation algorithms for the survivable network design problem in hypergraphs (SNDPHG) based on algorithms developed for the survivable network design problem in graphs (SNDP) or the element connectivity problem in graphs (ECP). Given an instance of the SNDPHG, by replacing each hyperedge e={v1,,vk} with a new vertex we and k edges {we, v1},, {we, vk}, we define an SNDP or ECP in the resulting graph. We show that by approximately solving the SNDP or ECP defined in this way, several approximation algorithms for the SNDPHG can be obtained. One of our results is a dmax+-approximation algorithm for the SNDPHG with dmax 3, where dmax (resp. dmax+) is the maximum degree of hyperedges (resp. hyperedges with positive cost). Another is a dmax+(rmax)-approximation algorithm for the SNDPHG, where (i)=j=1i(1/j) is the harmonic function and rmax is the maximum connectivity requirement.

The mobile computing system is a set of functions on a distributed environment organized to support mobile hosts. In this environment, mobile hosts should be able to move without any constraints and should remain connected to the network even while moving. Also, they should be able to get necessary information regardless of their current location and time. Distributed mutual exclusion methods for supporting distributed algorithms have hitherto been designed for networks only with static hosts. However, with the emergence of mobile computing environments, a new distributed mutual exclusion method needs to be developed for integrating mobile hosts with underlying distributed systems. In the sense, many issues that should be considered stem from three essential properties of mobile computing system such as wireless communication, portability, and mobility. Thus far, distributed mutual exclusion methods for mobile computing environments were designed based on a token ring structure, which has the drawback of requiring high costs in order to locate mobile hosts. In this paper, we propose not only a distributed mutual exclusion method that can reduce such costs by structuring the entire system as a tree-based logical structure but also recovery schemes that can be applied when a node failure occurs. Finally, we evaluate the operation costs for the mutual exclusion scheme and the recovery scheme.

A new logic-in-memory circuit is proposed for a fine-grain pipelined VLSI system. Dynamic-storage elements are distributed over a logic-circuit plane. A functional pass gate is a key component, where a linear summation and threshold function are merged compactly using charge-storage and charge-coupling effect with a DRAM-cell-based circuit structure. The use of dynamic logic based on pass-transistor network using functional pass gates makes it possible to realize any logic circuits compactly with small power dissipation. As a typical example, a 54-bit pipelined multiplier is implemented by using the proposed circuit technology. Its power dissipation and chip area are reduced to about 63 percent and 72 percent, respectively, in comparison with those of a corresponding binary CMOS implementation under 0.35-µm CMOS technology.

The stateless-based cache invalidation schemes for wireless environments can be categorized into either asynchronous or synchronous cache invalidation according to the broadcasting way of invalidation report. However, if the asynchronous cache invalidation scheme attempts to support local processing of read-only transaction, a critical problem may occur; the asynchronous invalidation reports provide no guarantee of waiting time for mobile transactions requesting commit. To solve this problem, the server in our approaches broadcasts two kind of messages, asynchronous invalidation report to reduce transaction latency and periodic guide message to avoid the uncertainty of waiting time for the next invalidation report. This paper presents a simulation-based analysis on the performance of the suggesting algorithms. The simulation experiments show that the local processing algorithms of read-only transaction based on asynchronous cache invalidation scheme get better response time than the algorithm based on synchronous cache invalidation scheme.

In this letter, sampling and quantizer design for the Gaussian detection problem are considered. A constraint on the transmission rate from the remote sensor to the optimal discrete detector is assumed. The trade-off between sampling rate and the number of quantization levels is studied and illustrated by means of an example.

A 1-V 2-GHz receiver that exhibits an image rejection of 49 dB is described. It consists of a low-noise amplifier, a quadrature mixer and on-chip polyphase filters, and was fabricated by 0.2-µm fully depleted CMOS/SIMOX technology. The quadrature mixer employs an LC-tuned folded structure with a common RF input for I and Q channels. This enables 1-V operation, suppresses phase errors in LO signals, and improves the image-rejection performance by about 15-dB compared to a conventional quadrature architecture. The current source of the single-to-balance converter at the mixer input consists of a transistor and an LC tank in a cascode configuration. This enhances its output impedance and improves its common-mode-rejection ratio (CMRR) and the IIP2 characteristics of the receiver. The chip consumes 12 mW with 1-V power supply. The receiver provides an NF of 10 dB with an IIP3 of -15.8 dBm and IIP2 of 12.3 dBm.

A fully on-chip active guard band circuit is proposed. The proposed circuit is mainly composed of current mirrors and based on a DC bias technique. HSPICE simulations and experiment results confirm the validity of the proposed active guard band circuit.

This paper describes an innovative, high-speed optical backboard bus composed of an optical star coupler, optical-transmitter modules, optical-receiver modules, and optical multi-mode glass fibers. A highly efficient optical coupling structure with an aspherical lens and a laser diode was designed to achieve a coupling efficiency of 90%, enabling distribution of optical signals at up to 1 Gb/s to 50 function boards. Embedded optical fibers in a printed circuit board were used to achieve precise control of the optical propagation delay times and permit a high packaging density. We developed small laser-diode and photo-diode modules suitable for optical coupling with the embedded fibers. A fabricated prototype optical backboard bus controlled by a controller IC mounted on a function board was able to successfully distribute high-speed optical signals to function boards with a high packaging density.

In this paper, we propose an activity-based estimation scheme to determine the received signal power disparity, that enhances the BER performance of the SIC scheme in a DS/CDMA system considering a practical voice activity factor, and compare BER performance with those of other schemes with or without estimation. Numerical analysis results show that the SIC scheme with the proposed activity-based estimation improves the BER performance compared with that without considering voice activity, and it approaches to that of the ideal estimation as the total number of concurrent users increases. In addition, the higher becomes the maximum attainable SNR, the better becomes the BER performance of the proposed activity-based estimation scheme.