A novel error detection method based on coded block pattern (CBP) information verification is proposed for error concealment of inter-coded video frames transmitted in wireless channel. This method firstly modifies the original video stream structure by the aggregation of certain important information, and then inserts some error verification bits into the video stream for each encoded macro block (MB), these bits can be used as reference information to determine whether each encoded MB is corrupted. Experimental results on additive Gauss white noise simulation wireless channel and H.263+ baseline codec show that the proposed method can outperform other reference approaches on error detection performance. In addition, it can preserve the original video quality with a small coding overhead increase.

In recent works [1],[4], it has been shown that the damping of a linear time invariant system relates to the so-called characteristic ratios (αk, k=1,…, n-1) which are defined by coefficients of the denominator of the transfer function. However, the exact relations are not yet fully understood. For the purpose of exploring the issue, this paper presents the analysis of time response sensitivity to the characteristic ratio change. We begin with the sensitivity of output to the perturbations of coefficients of the system denominator and then the first order approximation of the αk perturbation effect is computed by an explicit transfer function. The results are extended to all-pole systems in order to investigate which characteristic ratios act dominantly on step response. The same analysis is also performed to a special class of systems whose denominator is composed of so called K-polynomial. Finally, some illustrative examples are given.

New service concepts involving mobile devices with a diverse range of embedded sensors are emerging that share contexts supporting communication on a wireless network infrastructure. To promote these services in mobile devices, we propose a method that can efficiently detect a context provider by partitioning the location, time, speed, and discovery sensitivities.

A parallel notch filter (PNF) for eliminating a sinusoidal signal whose frequency and phase are unknown, has been proposed previously. The PNF achieves both fast convergence and high estimation accuracy when the step-size for adaptation is appropriately determined. However, there has been no discussion of how to determine the appropriate step-size. In this paper, we derive the convergence condition on the step-size, and propose an adaptive algorithm with variable step-size so that convergence of the PNF is automatically satisfied. Moreover, we present a new filtering structure of the PNF that increases the convergence speed while keeping the estimation accuracy. We also derive a variable step-size scheme for the new PNF to guarantee the convergence. Simulation results show the effectiveness of the proposed method.

The concept of grid computing emerged with the appearance of high-speed network. Effective grid worker (i.e., computing resource) selection mechanism is important to achieve reliable grid computing system since each worker participate in grid computing is heterogeneous. In this paper, we suggest a credible worker selection mechanism that maximizes grid computing performance by allocating appropriate tasks to each grid worker. Diverse workers can be used efficiently by grid applications through the ranking process of worker's credibility. Initially, the rank of each grid worker's credibility is decided considering static information only such as CPU speed, RAM size, storage capacity and network bandwidth. And then, the rank is refined by using dynamic information such as failure rate, turn around time provided after the task is completed, and correctness of the return value. In the experiments, we find that the proposed mechanism provides improved grid computing performance with high credibility.

An FRPA (frequency reuse power allocation) technique by employing the frequency reuse notion as a strategy for overcoming the ICI (intercell interference) and maintaining the QoS (quality of service) at the cell boundary is described for broadband cellular networks. In the scheme, the total bandwidth is divided into sub-bands and two different power levels are then allocated to sub-bands based on the frequency reuse for forward-link cell planning. In order to prove the effectiveness of the proposed algorithm, a Monte Carlo simulation was performed based on the Chernoff upper bound. The simulation shows that this technique can achieve a high channel throughput while maintaining the required QoS at the cell boundary.

In this letter, we study the capacity of fading channels with perfect channel side information (CSI) at the receiver and quantized CSI at the transmitter. We present a general algorithm for the joint design of optimal quantization and power control for maximizing the forward link capacity over flat fading channels. Numerical results for Rayleigh fading are given.

We report on the design and experimental results of a fix-tuned Superconductor-Insulator-Superconductor (SIS) mixer for Atacama Large Millimeter/submillimeter Array (ALMA) band 8 (385-500 GHz) receivers. Nb-based SIS junctions of a current density of 10 kA/cm2 and one micrometer size (fabricated with a two-step lift-off process) are employed to accomplish the ALMA receiver specification, which requires wide frequency coverage as well as low noise temperature. A parallel-connected twin-junction (PCTJ) is designed to resonate at the band center to tune out the junction geometric capacitance. A waveguide-microstrip probe is optimized to have nearly frequency-independent impedance at the probe's feed point, thereby making it easy to match the low-impedance PCTJ over a wide frequency band. The RF embedding impedance is retrieved by fitting the measured pumped I-V curves to confirm good matching between PCTJ and signal source. We demonstrate here a minimum double-sideband receiver noise temperature of 3 times of quantum limits for an intermediate-frequency range of 4-8 GHz. The mixers were measured in band 8 cartridge with a sideband separation scheme. Single-sideband receiver noise below ALMA specification was achieved over the whole band.

A chordal graph is a graph which contains no chordless cycle of at least four edges as an induced subgraph. The class of chordal graphs contains many famous graph classes such as trees, interval graphs, and split graphs, and is also a subclass of perfect graphs. In this paper, we address the problem of enumerating all labeled chordal graphs included in a given graph. We think of some variations of this problem. First we introduce an algorithm to enumerate all connected labeled chordal graphs in a complete graph of n vertices. Next, we extend the algorithm to an algorithm to enumerate all labeled chordal graphs in a n-vertices complete graph. Then, we show that we can use, with small changes, these algorithms to generate all (connected or not necessarily connected) labeled chordal graphs in arbitrary graph. All our algorithms are based on reverse search method, and time complexities to generate a chordal graph are O(1), and also O(1) delay. Additionally, we present an algorithm to generate every clique of a given chordal graph in constant time. Using these algorithms we obtain combinatorial Gray code like sequences for these graph structures in which the differences between two consecutive graphs are bounded by a constant size.

The Navigational Programming (NavP) methodology is based on the principle of self-migrating computations. It is a truly incremental methodology for developing parallel programs: each step represents a functioning program, and each intermediate program is an improvement over its predecessor. The transformations are mechanical and straightforward to apply. We illustrate our methodology in the context of matrix multiplication, showing how the transformations lead from a sequential program to a fully parallel program. The NavP methodology is conducive to new ways of thinking that lead to ease of programming and high performance. Even though our parallel algorithm was derived using a sequence of mechanical transformations, it displays certain performance advantages over the classical handcrafted Gentleman's Algorithm.

Resource management for infrastructure-based two-hop fixed relay systems which are applicable to TDD-FH-OFDMA based cellular systems with sectorization is proposed in this paper. The severe interference problem caused by both inter-sector and inter-cell can be tackled by employing 6-sector directional antennas combined with the resource allocation. The simulation results demonstrate that at the outer-region of the cell, the high data rate service coverage can be extended.

Flash bulk files downloading in style of P2P through perpendicular pattern becomes more popular recently. Many peers download different pieces of shared files from the source in parallel. They try to reconstruct complete files by exchanging needed pieces with other downloading peers. The throughput of entire downloading community, as well as the perceived downloading rate of each peer, greatly depends on uploading bandwidth contributed by every individual peer. Unfortunately, without proper built-in incentive mechanism, peers inherently tend to relentlessly download while intentionally limiting their uploading bandwidth. In this paper, we propose a both effective and efficient incentive approach--Reciprocity, which is only based on end-to-end measurement and reaction: a peer caps uploading rate to each of its peers at the rate that is proportional to its downloading rate from that one. It requires no centralized control, or electronic monetary payment, or certification. Preliminary experiments' results reveal that this approach offers favorable performance for cooperative peers, while effectively punishing defective ones.

We fabricated Josephson vortex flow transistors (JVFTs) with a parallel array of Josephson junctions that were prepared using c-axis-oriented 100-nm-thick YBa2Cu3O7-δ (YBCO) thin films grown on 24bicrystal MgO (100) substrates. We observed clear modulations of the critical current and the flow voltage with DC current input to the control line that was inductively coupled to the array of junctions. From the results, we estimated the parameters of the device, e.g., the mutual inductance and the self-inductance, and calculated the operation frequency at which the device potentially exhibited these parameters. Moreover, the current gain and the transresistance were evaluated and found to be 0.5 and 0.15 Ω, respectively. In addition, we observed the high-frequency responses of the JVFT to the input AC current of the sine wave or the square pulse wave. A clear oscillation of the output voltage could be observed with a 1 MHz sine wave and 250 kHz square pulse wave. We also discussed the feasibility of higher frequency operation by using it as an input interface for a single flux quantum (SFQ) logic circuit.

This paper describes a high-speed MT connector assembly method. This technique uses adhesive with a short hardening time, is highly reliable and does not require a polishing process, thus reducing the connector assembly time. First, we investigated an alpha-cyanoacrylate adhesive that hardens quickly and whose adhesive strength does not decrease under high humidity and high temperature conditions, thus ensuring its excellent reliability for outside use. In addition, we investigated variations in the position of the fiber endface on the ferrule endface with a view to obtaining a low insertion loss. Based on the results, we assembled an MT connector using our proposed high-speed assembly method. We confirmed that the assembly time could be reduced to less than 70% of the time required with the conventional method. MT connectors assembled using this technique have a low insertion loss and stable environmental characteristics.

We consider a network, where a special data called certificate is issued between two users, and all certificates issued by the users in the network can be represented by a directed graph. For any two users u and v, when u needs to send a message to v securely, v's public-key is needed. The user u can obtain v's public-key using the certificates stored in u and v. We need to disperse the certificates to the users such that when a user wants to send a message to the other user securely, there are enough certificates in them to get the reliable public-key. In this paper, when a certificate graph and a set of communication requests are given, we consider the problem to disperse the certificates among the nodes in the network, such that the communication requests are satisfied and the total number of certificates stored in the nodes is minimized. We formulate this problem as MINIMUM CERTIFICATE DISPERSAL (MCD for short). We show that MCD is NP-Complete, even if its input graph is restricted to a strongly connected graph. We also present a polynomial-time 2-approximation algorithm MinPivot for strongly connected graphs, when the communication requests satisfy some restrictions. We introduce some graph classes for which MinPivot can compute optimal dispersals, such as trees, rings, and some Cartesian products of graphs.

The guard channel scheme in wireless mobile networks has attracted and is still drawing research interest owing to easy implementation and flexible control. Dynamic guard channel schemes have already been proposed in the literature to adapt to varying traffic load. This paper presents a novel control-theoretic approach to dynamically reserve guard channels called PI-Guard Channel (PI-GC) controller that maintains the handoff blocking probability (HBP) to a predefined value; while it still improves the channel resource utilization.

The 2-vertex-connectivity augmentation problem for a specified set of vertices of a graph with degree constraints, 2VCA-SV-DC, is defined as follows: "Given an undirected graph G = (V,E), a specified set of vertices S ⊆V with |S|3 and a function g:V→Z+∪{∞}, find a smallest set E' of edges such that (V,E ∪E') has at least two internally-disjoint paths between any pair of vertices in S and such that vertex-degree increase of each v ∈V by the addition of E' to G is at most g(v), where Z+ is the set of nonnegative integers." This paper shows a linear time algorithm for 2VCA-SV-DC.

In this paper, we present Blueweb, a new Bluetooth-based multihop network with an efficient scatternet formation algorithm and a hybrid routing protocol. The Blueweb is designed from the original idea of Bluetree. Blueweb's scatternet formation uses two mechanisms. One is the role exchange mechanism in which only slave nodes serve as the role of relay through the whole scatternet. The other one is the return connection mechanism in which we convert the scatternet from a tree-shaped to a web-shaped topology. Meanwhile, a modified source routing protocol is designed for Blueweb in which we combine the proactive method with the reactive method to discover the optimal path for packet transmission. Furthermore, using computer simulations we compared the system performance of Blueweb and Bluetree with both a static model and a uniform traffic model. With the static model we evaluate the scatternet performance and with the uniform traffic model we evaluate the transmission performance. Our simulation results show that Blueweb achieves superior system performance than Bluetree on both scatternet performance and transmission performance.

The belief propagation (BP) algorithm is a tool with which one can calculate beliefs, marginal probabilities, of probabilistic networks without loops (e.g., Bayesian networks) in a time proportional to the number of nodes. For networks with loops, it may not converge and, even if it converges, beliefs may not be equal to exact marginal probabilities although its application is known to give remarkably good results such as in the coding theory. Tatikonda and Jordan show a theoretical result on the convergence of the algorithm for probabilistic networks with loops in terms of the theory of Markov random fields on trees and give a sufficient condition of the convergence of the algorithm. In this paper, we discuss the "impatient" update rule as well as the "lazy" update rule discussed in Tatikonda and Jordan. In the viewpoint of the theory of Markov random fields, it is shown that the rule for updating both gives essentially the same results and the impatient update rule is expected to converge faster than the lazy one. Numerical experiments are also given.

In 2000, Sandirigama, Shimizu, and Noda proposed a simple password authentication scheme, SAS. However, SAS was later found to be flawed. Recently, Chen, Lee, Horng proposed two SAS-like schemes, which were claimed to be more secure than similar schemes. Herein, we show that both their schemes are still vulnerable to denial-of-service attacks. Additionally, Chen-Lee-Horng's second scheme is not easily reparable.