Recently, Dutta and Barua proposed provably secure constant round authenticated group key agreement protocols in dynamic scenario. In this letter, we show that their Leave Protocol does not provide forward secrecy, that is, a leaving user can still obtain the new session key used in subsequent sessions.

In this paper, the relationship between correlation interval (CI) and estimate is investigated. Then a special correlation interval is explored that is adaptive to all levels of signal-to-noise ratio (SNR) and velocity conditions, and the mean square error is deduced. Finally, we propose an iterative algorithm that achieves the special correlation interval and calculates the Doppler spread by increasing the resolution on time-domain iteratively. Simulation results show that compared with conventional schemes, performance of the proposed algorithm is basically independent of velocity variation and less sensitive to SNR, especially in low SNR environments. It achieves high accurate estimation directly without any post-rectification.

This paper investigates the impact of chip duty factor (DF) in DS-UWB system with Rake receiver over AWGN and UWB indoor multipath environment corresponding to system parameters such as spreading bandwidth and chip length. Manipulating DF in DS-UWB system offers several advantages over multipath channel and thus, capable of improving system performance for better quality of communication. Although employing lower DF generally improves performance, in some exceptional cases on the other hand, degradation can be observed despite decreasing DF. Therefore, the objective of this paper is to clarify the relationship between DF and DS-UWB system performance. We discovered that with constant processing gain and spreading bandwidth, performance improvement can be observed at DF lower than 0.17. Additionally, with spreading bandwidth as tradeoff parameter, significant performance improvement can only be observed below DF of 0.85.

This paper presents a semi-blind algorithm for multiuser interference cancellation and fading amplitude estimation for downlink MIMO DS-CDMA systems with multipath fading channels. Taking advantage of the space-time information of the parametric multipath channel, the proposed algorithm first uses a space-time channel decoupler to suppress multiuser interference and then decomposes the channel into a set of parallel subchannels each containing the signal of the desired user on an individual multipath. Two criteria, the complementary orthogonal projection (COP) and the minimum variance distortionless response (MVDR), are employed by the space-time decoupler to achieve interference suppression and signal separation. The fading amplitudes can then be estimated from the eigen space of the output of the space-time channel decoupler. It follows that the signal of interest can be maximally combined in a pathwise manner and then differentially decoded.

In this paper, we propose a novel spatial filtering technique for orthogonal frequency division multiplexing (OFDM) signals called "VIrtual Subcarrier Assignment (VISA)." Here, virtual subcarrier is a subcarrier which is not used for data transmission. When a wireless terminal is equipped with multiple antennas, VISA can easily achieve a space division multiple access (SDMA) by assigning a different spectral position of virtual subcarrier to a different user. To realize VISA in an already-existing OFDM-based wireless local area network (WLAN), we discuss an antenna weight control method in the preamble of a signal burst format designed for the IEEE802.11a standard and evaluate the bit error rate (BER) performance in typical indoor wireless environments.

In this paper, a novel cost effective interconnection network for two-way pipelined SIMD-based reconfigurable computing processor is proposed. Our reconfigurable computing engine is composed of the SIMD-based function units, flexible interconnection networks, and two-bank on-chip memories. In order to connect the function units, the reconfigurable network is proposed to connect all neighbors of each function unit. The proposed interconnection network is a kind of full and bidirectional connection with the data duplication to perform the data-parallelism applications efficiently. Moreover, it is a multistage network to accomplish the high flexibility and low hardware cost.

For mobile visual communications, the development of more robust and efficient video traffic control and transmission techniques remains one of the most important issues. Foveated video originates from visual entropy reduction by removing undetectable high visual frequencies that occur at a distance from the fixation point. In this paper, compression gain is defined and measured to quantify the enhanced performance when the visual throughput of the regions of interest (ROI) is increased over a capacity-limited channel.

Object caching is a common feature in the scalable distributed object systems. Fine-grained replication optimizes the performance and resource utilization in object caching by enabling a remote object-oriented application to be partially and incrementally on-demand replicated in units of cluster. Despite these benefits, the lack of common and simple implementation framework makes the fine-grained replication scheme not extensively used. This paper proposes the novel frameworks for dynamic, transparent, partial and automatically incremental replication of distributed Java objects based on three techniques that are lazy-object creation, proxy and hook. One framework enables the fine-grained replication of server-side stateful in-memory application, and the other framework enables the fine-grained replication of server-side stateless in-memory application, client-side program, or standalone application. The experimental evaluation demonstrates that the efficiency in terms of response time of both frameworks are relatively practical to the extent of a local method invocation.

This letter proposed a linear precoding scheme for the V-BLAST system that requires only knowledge of the statistical CSI; the transmitter does not need the instantaneous CSI. Power allocation on the eigenmodes of the transmit correlation matrix is one way to minimize bit error rate (BER). Simulation results show that the proposed precoding V-BLAST system provides a significant reduction in the BER compared with the conventional V-BLAST systems.

In various applications of signals transmission and processing, there is always a possibility of loss of samples. The iterative algorithm of Papoulis-Gerchberg (PG) is famous for solving the band-limited lost samples recovery problem. Two problems are known in this domain: (1) a band-limited signal practically is difficult to be obtained and (2) the convergence rate is too slow. By inserting a subtraction by a polynomial in the PG algorithm, using boundary-matched concept, a significant increase in performance and speed of its convergence has been achieved. In this paper, we propose an efficient approach to restore lost samples by adding a preprocess which meets the periodic boundary conditions of Fast Fourier transform in the iteration method. The accuracy of lost samples reconstruction by using the PG algorithm can be greatly improved with the aid of mapping the input data sequence of satisfying the boundary conditions. Further, we also developed another approach that force the signal to meet a new critical boundary conditions in Fourier domain that make the parameters of the preprocessing can be easily obtained. The simulation indicates that the mean square error (MSE) of the recovery and the convergence rate with the preprocess concept is better and faster than the one without preprocess concept. Our both proposed approaches can also be applied to other cases of signal restoration, which allow Cadzow's iterative processing method, with more convenience and flexibility.

For broadband wireless networks based on OFDM (Orthogonal Frequency Division Multiplexing), an FRF (Frequency Reuse Factor) of 1 has been highly desirable for more improved channel throughput. However, due to the limited power budget of MSs (Mobile Stations) or the increase in ICI (Inter-Cell Interference), a required QoS (Quality of Service) may not be maintained. This paper addresses an optimal LCRTD (Loading Control based on Region-Time Division) over multi-cell environments for an efficient uplink QoS control. In the LCRTD scheme, a cell is divided into several regions by utilizing an optimization approach under QoS constraints, and users in each region are allowed to send their data at the allocated time slots. In the simulation, it is demonstrated that a decrease of 26% in the transmit power can be obtained.

A multiple-places reservation discipline is studied in a discrete-time priority queueing system. We obtain the joint distribution of system state, from which the delays of high and low priority packets are derived. Comparison is made with the cases of FIFO, single-place reservation discipline and HOL priority.

This paper proposes a new per-test fault diagnosis method based on the X-fault model. The X-fault model can represent all possible faulty behaviors of a physical defect or defects in a gate and/or on its fanout branches by assigning different X symbols assigned to the fanout branches. A partial symbolic fault simulation method is proposed for the X-fault model. Then, a novel technique is proposed for extracting more diagnostic information by analyzing matching details between observed and simulated responses. Furthermore, a unique method is proposed to score the results of fault diagnosis. Experimental results on benchmark circuits demonstrate the superiority of the proposed method over conventional per-test fault diagnosis based on the stuck-at fault model.

Martucci's Zero-tree Entropy (ZTE) coding algorithm exploits the advantages of discrete wavelet coding to improve the video quality of inter-frame coding. In this algorithm the wavelet tree is coded into three different tables, type, valz and valnz. Subsequently these three tables are arithmetic coded. However, the statistical variation of the distribution of the values and types are not considered in this categorization. We propose to decompose the zerotree such that this variation is taken into account. In our representation, values and the types are reorganized into hierarchical structures according to the sub band and the orientation. Our test results show that the proposed algorithm can reduce the bit rate per frame up to 73% over the Martucci's algorithm and performs better than EBCOT at higher bit rates.

In this letter, it is shown that a MAP detector can be employed with differential pulse-position modulation (L-DPPM) in an indoor optical wireless system. The MAP detector error performance is evaluated and compared with that of a hard-decision detector and MLSD over an intersymbol interference channel. It is shown that a MAP detector provides superb performance even in a dispersive channel with high DT.

Recently there are various requirements for LSI testing, such as test compaction, test compression, low power dissipation or increase of defect coverage. If test sequences contain lots of don't cares (Xs), then their flexibility can be used to meet the above requirements. In this paper, we propose methods for finding as many Xs as possible in test sequences for sequential circuits. Given a fully specified test sequence generated by a sequential ATPG, the proposed methods produce a test sequence containing Xs without losing stuck-at fault coverage of the original test sequence. The methods apply an approach based on fault simulation, and they introduce some heuristics for reducing the simulation effort. Experimental results for ISCAS'89 benchmark circuits show the effectiveness of the proposed methods.

We propose a semi-dynamic timing analysis flow applicable to large-scale circuits that takes into account dynamic power-supply drop. Logic delay is accurately estimated in the presence of power-supply noise through timing correction as a function of power-supply voltage during operation, where a time-dependent power-supply noise waveform is derived by way of a vectorless technique. Measurements and analysis of dynamic supply-noise waveforms and associated delay changes were performed on a sub-100-nm CMOS test circuit with embedded on-chip noise detectors and delay monitors. The proposed analysis technique was extended and applied to a test digital circuit with more than 10 million gates and validated toward a multi-10-million-gate CMOS SoC design.

Emerging GMPLS (Generalized Multi-Protocol Label Switching)-based photonic networks are expected to realize the dynamic allocation of network resources for a wide range of applications, such as carriers' backbone networks as well as enterprise core networks and GRID computing. To address diverse reliability requirements corresponding to different application needs, photonic networks have to support various optical path recovery schemes. Thus GMPLS standardization bodies have developed failure recovery protocols for 1+1 protection, 1:N protection and restoration, with support of extra traffic and shared use of back-up resources. Whereas the standardization efforts cover a full spectrum of recovery schemes, there have not been many reports on actual implementations of such functionalities, and none of them included extra traffic. This paper introduces an OXC (Optical Cross Connect) implementation of GMPLS's failure recovery functionalities supporting 1+1 protection, M:N protection and extra path. Here extra path is an extension of GMPLS protection's extra traffic which can partially reuse protected paths' back-up resources. Evaluation of the implementation confirms rapid recovery of protected traffic upon a failure, even when preemption of an extra path is involved. It is also shown that its preemption scheme can resolve the issue of the poor scalability of GMPLS-based preemption when multiple extra paths are preempted upon a failure.

The output limits of the power system stabilizer (PSS) can improve the system damping performance immediately following a large disturbance. Due to non-smooth nonlinearities from the saturation limits, these values cannot be determined by the conventional tuning methods based on linear analysis. Only ad hoc tuning procedures have been used. A nonlinear least squares method, which is the Gauss-Newton optimization algorithm, is used in this paper. The gradient required in the Gauss-Newton method can be computed by applying trajectory sensitivities from the hybrid system model with the differential-algebraic-impulsive-switched (DAIS) structure. The optimal output limits of the PSS tuned by the proposed method are evaluated by time-domain simulation in a multi-machine power system (MMPS).

This paper presents an algorithm-level interpretation of fast adder structures in binary/multiple-valued logic. The key idea is to employ a unified representation of addition algorithms called Counter Tree Diagrams (CTDs). The use of CTDs makes it possible to describe and analyze addition algorithms at various levels of abstraction. A high-level CTD represents a network of coarse-grained components associated with multiple-valued logic devices, while a low-level CTD represents a network of primitive components directly mapped onto binary logic devices. The level of abstraction in circuit representation can be changed by decomposition of CTDs. We can derive possible variations of adder structures by decomposing a high-level CTD into low-level CTDs. This paper demonstrates the interpretation of redundant arithmetic adders based on CTDs. We first introduce an extension of CTDs to represent possible redundant arithmetic adders with limited carry propagation. Using the extended version of CTDs, we can classify the conventional adder structures including those using emerging devices into three types in a systematic way.