The Internet and mobile communication systems are being developed, and related applications for managing personal information require user authentication for confirming legitimate users. One-time password authentication methods secure user's authorities by changing the verifier every time. The S/Key is a famous one-time password authentication scheme, which is based on Lamport's scheme. T.-C. Yeh et al. have point out security problems of the S/Key scheme and have proposed a variant of the S/Key scheme, which can be applied to smart cards. However, this method risks certain attacks, too. Those two proposed schemes use counter value, which can easily be modified by an attacker. Herein we discuss security problems of the S/Key and Yeh-Shen-Hwang's password authentication schemes using forgery attacks and stolen-verifier attacks.

In this paper, we consider QoS-guaranteed wavelength allocation for WDM networks with limited-range wavelength conversion. In the wavelength allocation, the pre-determined number of wavelengths are allocated to each QoS class depending on the required loss probability. Moreover, we consider two wavelength selection rules and three combinations of the rules. We analyze the connection loss probability of each QoS class for a single link using continuous-time Markov chain. We also investigate the connection loss probability for a uni-directional ring network by simulation. In numerical examples, we compare connection loss probabilities for three combinations of selection rules and show how each combination of selection rules affects the connection loss probability of each QoS class. Furthermore, we show how wavelength conversion capability affects the connection loss probability. It is shown that the proposed allocation with appropriate wavelength selection rule is effective for QoS provisioning when the number of wavelengths is large. We also show the effective combination of wavelength selection rules for the case with small wavelength conversion capability.

This paper proposed a watermarking algorithm for image, which assumed an image compression based on DWT (Discrete Wavelet Transform). To reduce the amount of computation, this algorithm selects the watermarking positions by a threshold table which is statistically established from computing the energy correlation of the corresponding wavelet coefficients. The proposed algorithm can operate in a real-time if the image compression process operates in a real-time because the watermarking process was designed to operate in parallel with the compression process. Also it improves the property of losing the watermak and reducing the compresson ratio by the quantization and Huffman coding steps. It was done by considering the sign of the coefficients and the change in the value for watermarking. Visually recognizable pattern such as a binary image were used as the watermark. The experimental results showed that the proposed algorithm satisfied the properties of robustness and imperceptibility that are the major conditions of watermarking.

The unpredictable behavior of cache memory makes it difficult to statically analyze the worst-case performance of real-time systems. This problem is further exacerbated in the case of preemptive multitask systems because of inter-task cache interference, called Cache-Related Preemption Delay (CRPD). This paper proposes an approach to analyzing the tight upper bound on CRPD which a task might impose on lower-priority tasks. Our method finds the program execution path which requires the maximum number of cache blocks using an integer linear programming technique. Experimental results show that our approach provides up to 69% tighter bounds on CRPD than a conservative approach.

The relative window method provides quantitative crosstalk delay degradation for the post-layout timing analysis in deep sub-micron VLSI design. However, to the best of our knowledge, the relative window method has not been applied to the crosstalk minimization in gridded channel routing problem. Most conventional crosstalk optimizers only use the coupling length to estimate the crosstalk. In this paper, we present a post-layout timing driven crosstalk optimizer based on the relative window method. According to the relative signal arrival time and the coupling length, we define a delay degradation graph to describe the crosstalks between nets in a routing solution. Our optimization goal is to maximize the time slack by iteratively improving the delay degradation graph without increasing the channel height. Benchmark data consistently show that our post-layout timing driven crosstalk optimizer can further improve the routing solution obtained by a conventional crosstalk optimizer.

Evaluation of cyclic transitions in the discrete-time neural networks with antisymmetric and circular interconnection weights has been derived in an asymptotic mathematical form. The type and the number of limit cycles generated by circular networks, in which each neuron is connected only to its nearest neurons, have been investigated through analytical method. The results show that the estimated numbers of state vectors generating n- or 2n-periodic limit cycles are an exponential function of (1.6)n for a large number of neuron, n. The sufficient conditions for state vectors to generate limit cycles of period n or 2n are also given.

This paper describes a new speech enhancement system that employs a microphone array with post-processing based on minimum mean-square error short-time spectral amplitude (MMSE-STSA) estimator. To get more accurate MMSE-STSA estimator in a microphone array, modification and refinement procedure are carried out from each microphone output. Performance of the proposed system is compared with that of other methods using a microphone array. Noise removal experiments for white and pink noises demonstrate the superiority of the proposed speech enhancement system to others with a microphone array in average output SNRs and cepstral distance measures.

Ad Hoc Networks are transmission networks in the structure of wireless networks that consist of many mobile hosts. They do so without the support from other communication infrastructures like Base Stations, and directly use wireless networks for data-transmission. This paper provides a general explanation of related protocols for setting up routes and their possible problems. In addition, related researches are described with their method of solving problems and reducing the possibility of problems occurring. Then, a novel constructive protocol called Partition-Timing Routing Protocol (PTR) is presented. If any covered node needs to transmit data to others outside the scope, it has to be managed by a core node. This protocol is able to adjust neighboring nodes covered in the scope, to select certain nodes to be their own core node. In addition, the timing for updating and adjusting the data of the covered scope is different from other methods, and at the same time it reduces the load of the entire network and makes it more flexible.

This letter evaluates the peak-to-average power ratio (PAR) performance in a space-time block coded (STBC) multicode CDMA (MC-CDMA) system using a selected mapping (SLM) approach. The ordinary method is to apply the SLM scheme for each transmit antenna individually, while the investigated SLM-based STBC MC-CDMA system selects the transmitted sequence with the lowest average PAR over all transmit antennas concurrently. SLM-based STBC MC-CDMA system retrieves the side information very accurately at the expense of a slight degradation of the PAR performance, which can improve the overall detection performance of the STBC MC-CDMA system in the presence of erroneous side information compared to the ordinary SLM approach.

A band-pass delta-sigma modulator (BPDSM) is a key building block to implement a digital intermediate frequency (IF) receiver in a wireless communication system. This paper proposes a time-interleaved (TI) switched-capacitor (SC) BPDSM architecture that consists of 5-stage TI blocks with recursive loop. The proposed TI BPDSM provides reduction in the clock frequency requirement by a factor of 5 and relaxes the settling time requirement to one-fourth of conventional approach. The test chip was designed and fabricated for a 30-MHz IF system with a 0.35-µm CMOS process. The measured peak SNR for a 200-kHz bandwidth is 63 dB while dissipating 75 mW from a 3.3-V supply and occupying 1.3 mm2.

Band Division MC-CDM (BD-MC-CDM) has been proposed for high quality wireless communications and has been investigated in terms of link level performance. In this paper, we investigate frequency band and time slot selection technique from the viewpoint of system level performance in order to realize the efficient BD-MC-CDM system under cellular environments. Then a downlink frequency band and time slot selection scheme is proposed for cellular BD-MC-CDM systems. The proposed scheme selects transmission frequency band according to the signal-to-interference ratio (SIR) estimated by using the pilot signal at mobile stations and also selects transmission time slot by using the SIR threshold. Simulation results show that the proposed scheme improves the downlink throughput but degrades delay performance and it has a trade off between throughput and delay performance. By selecting suitable control parameters, the proposed scheme achieves the throughput improvement without sacrificing the delay performance.

We propose Max-Plus Linear (MPL) systems with selective parameters that can describe a certain class of Timed Petri nets (TPN). In this class, selector and joint places are incorporated with Single-Input and Single-Output Timed Event Graph (SISO TEG) subnets. We confirm that the proposed controller effectively works taking into account practical constraints through a numerical example.

Transitional fundamental frequency (F0) characteristics comprise a crucial part of F0 dynamics in singing. This paper examines the F0 characteristics during the note transition period. An analysis of the singing voice of a professional baritone strongly suggests that asymmetries exist in the mechanisms used for controlling rising and falling. Specifically, the F0 contour in rising transitions can be modeled as a step response from a critically-damped second-order linear system with fixed average/maximum speed of change, whereas that in falling transitions can be modeled as a step response from an underdamped second-order linear system with fixed transition time. The validity of the model is examined through auditory experiments using synthesized singing voice.

In communication systems such as mobile telecommunication systems and the Internet, resource sharing among coexisting real-time and non-real-time services is extremely important to provide multimedia services. This paper analytically investigates the performance of the packet data control algorithm proposed in. This algorithm efficiently uses radio resources by utilizing the remaining capacity that is not used by real-time services. The state probability vectors and transition probability matrices of both the real-time and non-real-time services are first derived and then the delay characteristics, the outage probability of voice users, and the outage probability of data users are evaluated. A performance analysis with high bit-rate non-real-time services is also presented.

We present a new space-time successive interference cancellation (ST-SIC) scheme with multiple transceiver antennas for direct-sequence code division multiple access (DS-CDMA) systems. The proposed scheme is computationally very efficient, while maintains the performance close to the previous space-time multiuser detection (ST-MUD) scheme. The bit error rate (BER) performance of the ST-SIC scheme for coherent phase shift keying (PSK) modulation is analytically examined in Rayleigh fading channels, and its validity and usefulness are demonstrated by computer simulations.

We study the user reneging behavior in a hybrid Multimedia-on-Demand (MoD) system, which provides both interactive and batch services. Reneging happens when users become reluctant to wait for a batch service and quit the service. They will either join the interactive service or quit the system. In this letter, the analytical model for the MoD system with user reneging behavior is provided. Numerical results show that the reneging behavior has a significant impact on system performance. Therefore, careful consideration on reneging behavior should be made for designing a MoD system.

A variety of real-time multicast applications such as video conferences, remote lectures, and video-on-demand have become in commonplace with the expansion of broadband Internet services. Due to nontrivial problems in the IP multicast technology, the peer-to-peer multicast technology (P2P-multicast) has emerged as a practical implementation, although its network resource utilization is less efficient. A multihome network has the potential of alleviating this inefficiency by providing flexibility in communication path selections for each host with multiple gateways to the Internet. This paper has first formulated the P2P-multicast routing problem in the multihome network, and has proved the NP-completeness of its decision problem. Then, a two-stage heuristic algorithm called P2PMM_router has been presented for this P2P Multicast Multihome-network routing problem. The first stage constructs an initial multicast routing tree from an optimum spanning tree by Prim algorithm, through satisfying the constraints. The second stage improves the tree by repeating partial modifications and constraint satisfactions. The extensive simulation results using random network instances support the effectiveness of our P2PMM_router.

This paper considers Quasi-Reduced ordered Multi-valued Decision Diagrams with k bits (QRMDD(k)s) to represent binary logic functions. Experimental results show relations between the values of k and the numbers of nodes, the memory sizes, the numbers of memory accesses, and area-time complexity for QRMDD(k). For many benchmark functions, the numbers of nodes and memory accesses for QRMDD(k)s are nearly equal to of the corresponding Quasi-Reduced ordered Binary Decision Diagrams (QRBDDs), and the memory sizes and the area-time complexities for QRMDD(k)s are minimum when k = 2 and k = 3-6, respectively.

IP multicast is seen as an efficient way of encouraging multimedia services such as Internet TV and Videoconferencing because it can deliver packets to multiple users while efficiently using network resources. Source Specific Multicast (SSM) is suggested as the IP multicast routing protocol and it can construct multicast trees efficiently. However it increases multicast forwarding table entries and fails to handle source mobility. This paper proposes the Unicast Extension Multicast Protocol (UMP) to solve these problems. In the protocol, only the routers that act as branching points keep multicast forwarding table entries, and packets are delivered between these routers using IP unicast. This prevents the multicast forwarding table entries from burdening other non-branch routers. Additionally, UMP supports source mobility by using the recursive join messages to prevent the creation of redundant paths while supporting source mobility.

In this letter, we propose a packet scheduling algorithm to support both real-time voice and video traffic for wireless multimedia data service in orthogonal frequency division multiple access (OFDMA) system. Our design objective is to maximize the number of real-time service users that can be supported in the system subject to QoS requirement of packet loss rate (PLR). Both time slots and subcarriers are taken into account as the basic resource allocation unit in OFDMA/FDD system. The simulation results show that our proposed algorithm can dramatically increase the number of users satisfying the underlying QoS requirement for the real-time service, as compared to the existing algorithm.