The issue of guaranteeing Quality of Services (QoS) in a network has emerged in recent years. The Proportional Delay Differentiated Model has been presented to provide the predictable and controllable queueing delay differentiation for different classes of connections. However, most related works have focused on providing this model for a wired network. This study proposes a novel scheduler to provide proportional delay differentiation in a wireless network that includes a multi-state link. This scheduler, Look-ahead Waiting-Time Priority (LWTP), offers proportional delay differentiation and a low queueing delay, by adapting to the location-dependent capacity of the wireless link and solving the head-of-line (HOL) blocking problem. The simulation results demonstrate that the LWTP scheduler actually achieves delay ratios much closer to the target delay proportion between classes and yields smaller queueing delays than past schedulers.

Diagonal algebraic space time (DAST) block codes was proved to achieve the full transmit diversity over a quasi-static fading channel and to maintain 1 symbol/s/Hz. When the number of transmit antennas employed is larger than 2, DAST codes outperform the codes from orthogonal design with the equivalent spectral efficiency. However, due to the limitation on the signal constellation with complex integer points, no good 3bits/symbol DAST block code was given previously. In this paper, we propose a general form of 8-star-PSK constellations with integer points and present some theoretical results on the performance of the equivalent 8-star-PSK modulations. By using our proposed 8-star-PSKs, we present a searching algorithm to construct DAST codes with 3 bits per symbol under some criteria and investigate their performances over flat Rayleigh fading channels. It is shown that (5,2) 8-star-PSK scheme has a comparable performance to conventional 8PSK over additive white Gaussian noise (AWGN) channel and the corresponding DSAT codes constructed can achieve significant performance gain over flat Rayleigh fading channel.

In this paper, two efficient VLSI architectures for biorthogonal wavelet transform are proposed. One is constructed by the filter bank implementation and another is constructed by the lifting scheme. In the filter bank implementation, due to the symmetric property of biorthogonal wavelet transform, the proposed architecture uses fewer multipliers than the orthogonal wavelet transform. Besides, the polyphase decomposition is adopted to speed up the processing by a factor of 2. In the lifting scheme implementation, the pipeline-scheduling technique is employed to optimize the architecture. Both two architectures are with advantages of lower implementation complexity and higher throughput rate. Moreover, they can also be applied to realize the inverse DWT efficiently. Based on the above properties, the two architectures can be applied to time-critical image compressions, such as JPEG2000. Finally, the architecture constructed by the lifting scheme is implemented into a single chip on 0.35 µm 1P4M CMOS technology, and its area and working performance are 5.005 5.005 mm2 and 50 MHz, respectively.

We consider vector channel estimation for differentially modulated systems with transmit diversity. We propose a blind estimation scheme to yield superior performance to that of the pilot-aided estimation. The proposed scheme utilizes the repeated transmission of space-time coded data symbols. We compare the performance of the proposed blind scheme with the pilot-based estimation scheme via computer simulations.

For network computing on desktop machines, fast execution of Java bytecode programs is essential because these machines are expected to run substantial application programs written in Java. We believe higher Java performance can be achieved by exploiting instruction-level parallelism (ILP) in the context of Java JIT compilation. This paper introduces VLaTTe, a Java JIT compiler for VLIW machines that performs efficient scheduling while doing fast register allocation. It is an extended version of our previous JIT compiler for RISC machines called LaTTe whose translation overhead is low (i.e., consistently taking one or two seconds for SPECJVM98 benchmarks) due to its fast register allocation. VLaTTe adds the scheduling capability onto the same framework of register allocation, with a constraint for precise in-order exception handling which guarantees the same Java exception behavior with the original bytecode program. Our experimental results on the SPECJVM98 benchmarks show that VLaTTe achieves a geometric mean of useful IPC 1.7 (2-ALU), 2.1 (4-ALU), and 2.3 (8-ALU), while the scheduling/allocation overhead is 3.6 times longer than LaTTe's on average, which appears to be reasonable.

The ATM Forum recommends the use of the Generic Cell Rate Algorithm (GCRA) to perform Usage Parameter Control at the User Network Interface of ATM networks. In order to facilitate the Call Admission Control and resource allocation procedure, it is important to investigate the characteristics of the model in which GCRA-enforced sources are merged together by a multiplexer. Such a multiplexer could be the one arranged in front of a switch to concentrate user traffic and reduce the number of required input ports. It may also represent the logical multiplexer at the output port of a switch that collects cells routed from various input ports. Moreover, it may represent the service function of the edge router situated between the integrated-services (IntServ) networks and the backbone networks that provide differentiated-services (DiffServ). In this paper, the environment under discussion is a multiplexer in which every traffic source is enforced by a dual-stage GCRA enforcer before being merged. The worst traffic pattern that maximizes the average waiting time in the multiplexer is found. The maximum average waiting time is deduced and expressed as a function of the GCRA parameters and the number of multiplexed sources. In particular, the analysis considers the speed-up function, which is widely used for ATM multiplexers and switches. The results can also be applied to a GCRA shaper without any modification.

Timing noise of 160 GHz optical pulses has been evaluated over nine decades of Fourier frequency using the optoelectronic harmonic mixing technique. For down-converting the 160 GHz pulse intensity into a low-frequency IF signal, the fourth order modulation sidebands produced by a Mach-Zehnder intensity modulator have been employed. Phase noise power spectral density and timing jitter for 155.552-GHz optical time-division multiplexed pulses and 160.640-GHz passively mode-locked pulses are measured using the time domain demodulation and time interval analysis techniques, respectively.

In this paper, we consider a location management scheme using Limited Pointer forwarding from Commonly visited sites (LPC) strategy for Personal Communication Services (PCS) networks. The Commonly Visited Site (CVS) is defined as a site in which a mobile user is found with high probability. A feature of the strategy is that it skips updating location information of the mobile user, provided that the mobile user moves within its CVSs. Such a strategy is expected to significantly reduce the location update cost. We evaluate the location management cost of the LPC scheme by employing a Continuous-Time Markov Chain (CTMC) model. We show that the LPC scheme can reduce the location management cost of a highly mobile user who is found in its CVS with high probability.

This paper proposes an analytical model to demonstrate the benefit of data service in wireless networks using dynamic multi-channel scheme with channel de-allocation. The performance of a system providing buffers to voice calls to reduce the raised voice blocking probability caused by data contention is investigated. The effect of the cell dwell time and overlap area with adjacent cells on system performance are studied. All free channels are allocated to data users dynamically. For those data users using more than one channel, channels would be de-allocated for new requests, voice or data. Buffers are provided for voice calls to reduce the voice blocking probability caused by data packets contention. Handoff calls are given priority to be queued in the front of the buffer instead of providing guard channels to reduce their dropping probability. Meanwhile, the reneging time for new calls and the handoff dwell time for handoff calls are considered in our analysis to obtain an appropriate amount of buffer to voice. To compensate the blocking probability in data, guard channels are provided for data traffic. Numerical results show that the dynamic multi-channel scheme with possible de-allocation, compared with the single channel scheme, can enhance data traffic performance significantly in terms of the mean transmission time and blocking probability. A system providing an appropriate amount of buffer to voice traffic and giving priority to queued handoff calls can indeed reduce new call blocking probability and handoff call dropping probability. In addition, the proposed scheme can reduce the incomplete transmission probability of data packets.

In this paper, we propose a statistical method of time synchronization for computer clocks that have precisely frequency-synchronized oscillators. This method not only improves the accuracy of time synchronization but also prevents degradation in the frequency stability of the precise oscillators when the errors in the measured time offsets between computer clocks caused by network traffic possess a Gaussian distribution. Improved accuracy of time synchronization is achieved by estimating the confidence interval of the measured time offsets between the clocks. Degradation in frequency stability is prevented by eliminating unnecessary time correction for the computer clock, because time correction generally causes changes in the frequency accuracy and stability of the precise oscillators. To eliminate unnecessary time correction, our method uses an extended hypothesis test of the difference between the current mean and the mean at the last time adjustment to determine whether time correction is needed. Evaluation by simulating changes in the time offset of the existing ISDN clock synchronization system showed that this method achieves accurate time and stable frequency synchronization.

Applications for transforming money or personal information are increasingly common on the Internet and in mobile communications. These applications require user authentication for confirming legal users. One-time password authentication methods change the verifier every time by sending the present verifier along with the next verifier. However, such methods risk attacks because those protocols use two verifiers every session. The SAS (Simple And Secure password authentication protocol) is a one-time password authentication method that the method uses a hash function five times, but it requires high overhead on low spec machines. In this paper, we propose a new method, SAS-2, which reduces overhead of hash function adaptation by 40%. This method has a mutual authentication phase, which maintains synchronous data communications in its authentication procedure. Moreover, SAS-2 can be applied to key-free systems.

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.

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.

Modern spaceborne precision radar altimeters transmit radio signals of a spectrum bandwidth up to 300 MHz, but the bandwidth should be still increased for precise estimation of the roughness of the sea surface. In this research, the influence of the ionosphere on wideband radar signals is investigated and then it is shown that the signals are strongly influenced by the dispersive distortions in the atmosphere of the Earth even in Ku-band. Finally, the allowable bandwidth of a space borne precision radar altimeter signals is estimated, at which we could ignore the presence of these distortions.

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.

We have been developing new cycling environments by using knowledge sharing and speech communication. We have offered multimodal knowledge contents to share knowledge on safe and exciting cycling. We accumulated 140 contents, focused on issues such as riding techniques, trouble shootings, and preparations on cycling. We have also offered a new way of speech communication using an ad-hoc wireless LAN technology for safe cycling. Group cycling requires frequent communication to lead the group safely. Speech communication achieves spontaneous communication between group members without looking around or speaking loudly. Experimental result through actual cycling has shown the effectiveness of sharing multimodal knowledge contents and speech communication. Our new developed environment has an advantage of increasing multimodal knowledge through the accumulation of personal experiences of actual cycling.

In this paper, we propose a method of linear time-varying filtering of discrete time signals. The objective of this method is to derive a component, of an input signal, whose alias-free generalized discrete time-frequency distribution [Jeong & Williams 1992] concentrates on a specific region of a time-frequency plane. The method is essentially realized by computing an orthogonal projection of an input onto a subspace that is spanned by orthonormal signals, whose distributions concentrate on the region. We show that such orthonormal signals can be derived as eigenvectors of a matrix whose components are explicitly expressed by using the kernel of the distribution and the regions. This result shows that we can design such a filter prior to processing of the input if the specific region is given as a priori. This result is a generalization of [Hlawatsch & Kozek 1994], that is originally derived for the continuous Wigner distributions, to the discrete distributions.

A robust watermarking scheme based on the time-spread echo method is proposed in this letter. The embedding process is achieved by subband decomposition of a host signal and by controlling the amount of distortion, i.e., power of watermark, of each subband according to the Signal to Mask Ratio (SMR) calculated from MPEG psychoacoustic model. The decoding performance and robustness of the proposed method were evaluated.

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 article we analyze the performance of a space division output buffered multichannel switch operating in an ATM multimedia environment as follows. Fixed size packets belonging to two classes arrive onto the switch inputs in each time slot. Class-1 packets, representing real time traffic such as live audio and live video communications, are sensitive to delay but insensitive to loss and have their own service time needs. Class-2 packets, representing nonreal time communications such as file transfers, are insensitive to delay but sensitive to loss and have their different service time needs. To respond to the class-1 delay sensitivity, the switch gives class-1 packets higher service priority over class-2. And to respond to the difference in service time needs, the switch operates at two service rates, one for each class. This latter assumption is the major feature of the article, as previous studies have usually assumed that the two classes have the same service needs and thus the same service rate. For the purpose of the analysis, the switch is modelled as a priority, discrete time, batch arrival, multiserver queueing system, with infinite buffer and two geometric service times with two parameters. Performance measures analyzed are system occupancy and packet waiting time.