In cellular systems, a code division multiple access (CDMA) technology with array antennas can significantly reduce interferences by taking advantage of the combination of spreading spectrum and spatial filtering. We investigate performance of cellular CDMA systems through adopting two types of array antennas, switched beam forming (SBF) and tracking beam forming (TBF) in the base station. Through Monte-Carlo simulations, we evaluate average bit-error-rate (BER) and outage probability of the systems under log-normal shadowing channels with multi-cell environment. When we consider 2 beams and 4 beams per sector for the SBF method, it is observed that the TBF method gives at least 10% and 30% capacity improvement over the SBF method in aspects of 10-3 BER and 1% outage probability, respectively.

In recent years, interruption of services large-scale business sites and Root Name Servers caused by Denial-of-Service (DoS) attacks or Distributed DoS (DDoS) attacks has become an issue. Techniques for specifying attackers are, thus important. On the other hand, since information on attackers' source IP addresses are generally spoofed, tracing techniques are required for DoS attacks. In this paper, we predict network traffic volume at observation points on the network, and detect DoS attacks by carefully examining the difference between predicted traffic volume and actual traffic volume. Moreover, we assume that the duration time of an attack is the same at every observation point the attack traffic passes, and propose a tracing method that uses attack duration time as a parameter. We show that our proposed method is effective in tracing DDoS attacks.

Iterative multiuser detection and space-time coding are two promising techniques to increase the capacity and performance of coded multiuser systems in wireless channels. In this paper, a low-complexity iterative multiuser receiver is proposed using combined group multiuser detection and interference cancellation for space-time block coded MC-CDMA system. Turbo code is used for outer channel coding with log-MAP decoding. In each group, consisting of smaller number of users, multiuser likelihood ratios can be computed by employing MAP-based approach by taking into account of all possible transmitted symbols within each STBC time slot for these users. Moreover, once decoding information of all users are available after the first iteration, soft interference cancellation can be used instead of groupwise MAP-based detection for lower complexity, without sacrificing the performance significantly. Simulation results are presented in a Rayleigh multipath fading environment. The proposed receiver offers performance very close to that of single user system within a few iterations of joint detection and decoding.

In this paper, a test architecture optimization for system-on-a-chip under floorplanning constraints is proposed. The models of previous test architecture optimizations were too ideal to be applied to industrial SOCs. To make matters worse, they couldn't treat topological locality of cores, that is, floorplanning constraints. The optimization proposed in this paper can avoid long wires for TAMs in consideration of floorplanning constraints and finish optimizing test architectures within reasonable computation time.

This paper presents a performance comparison between carrier interferometry coded OFDM (CI/COFDM) and typical coded OFDM (COFDM) using multiple receive antennas. The feature of CI/COFDM with diversity reception is to combine the time diversity benefit introduced by channel coding with the frequency and space diversity benefits created by frequency-domain equalization (FDE). Simulation results for QPSK showed that, at the perfect channel estimation, CI/COFDM outperforms COFDM under frequency and time selective fading channels because of the powerful time diversity benefit introduced by channel coding with time interleaving. However, at the imperfect channel estimation, this advantage of CI/COFDM over COFDM becomes very limited.

In this paper, the bit error rate (BER) and the outage probability are presented for a maximal ratio combining (MRC) two-dimensional (2D)-RAKE receiver operating in a correlated frequency-selective Nakagami-m fading environment with multiple access interference. A simple approximated probability distribution function of the signal-to-interference-plus-noise ratio (SINR) is derived for the receiver with multiple correlated antennas and RAKE branches in arbitrary fading environments. The combined effects of spatial and temporal diversity order, average received signal-to-noise ratio, the number of multiple access interference, angular spread, antennae spacing and multi-path Nakagami-m fading environment on the system performance are illustrated. Numerical results indicate that the performance of the 2D-RAKE receiver depends highly on the operating environment and antenna array configuration. The performance can be improved by increasing the spatio-temporal diversity gains and antenna spacing.

In this paper, we investigate a low-power architecture for designs modeled as an Extended Finite State Machine (EFSM). It is based on the general dynamic power management concept, in which the redundant computation can be dynamically disabled to reduce the overall power dissipation. The contribution of this paper is mainly a systematic procedure to identify almost maximal amount of redundant computation in a design given as an EFSM. There are two levels of redundant computation to be exploited--one is based on the machine state information, while the other is based on the transition information. After the extraction of the redundant computation, a low-power architecture using input gating is proposed to synthesize the final circuit. We tested the technique on a design computing a number's modulo inverse. Experimental results show that 31% power reduction can be achieved at the costs of 2% timing penalty and 16% area overhead.

The notion of effective bandwidth provides an elegant and powerful mathematical basis for the provision of QoS-assured services over IP networks. In this paper, we propose a semi-parametric estimator of effective bandwidth, called Gaussian estimator using buffer masurement, for superposition of sources in IP networks. In contrast to most existing proposals concerning the effective bandwidth estimator, our proposal works based on a small set of measurements of the workload in the buffer of a router. We analytically show the property of the proposed estimator with respect to the dependence on the service rate. We provide numerical results to show that our proposed estimator is more accurate than estimators that rely only on the amount of traffic from sources.

Phase performance in a temperature sensor using a conventional single-mode step-index fiber is studied. Two modes are excited in a so called single-mode fiber when the wavelength of a laser source is shorter than the one suggested by the specification of a fiber. The phase shift due to the temperature change of a step-index fiber is analyzed. The intensity fluctuation by the interference of two modes is observed in the experiment and estimated in the computer simulation.

In this letter, a generalized extension of the linear Z4 space time (ST) code of [1] is conducted to obtain a linear Zw structure that can be flexibly used for various numbers of transmitter antennas, number of states, and modulation types. Additionally, the corresponding recursive systematic (RS) code structure is presented. The optimal code of the quadrature phase shift keying (QPSK) and 8 phase shift keying (PSK) modulation with 2 transmit antenna case is obtained from a code search and analyzed in comparison to the codes of [5]. Additionally, the structure for the 8, 32, and other number of states that were not provided in are [1] presented in this paper.

The multiple space-time trellis codes (M-STTC) structure is one of the Multiple Input Multiple output (MIMO) schemes providing high transmission rate and diversity and coding gain without bandwidth expansion. In this paper, an M-STTC system is proposed wherein the transmitter employs a multiple space-time TCM for the fast fading channel and the receiver has a decoding order block, several whitening processors, STTC decoders, and interference cancellers. The proposed layered receiver adopts a whitening process instead of a minimum mean squared error (MMSE) estimator, which is widely used in the BLAST type receiver. An optimum decoding order scheme is also planned since it gives at least a 2 dB gain in the proposed system in the fast flat Rayleigh fading channel of fd Tc = 1/3 at the FER of 10-2. For an M-STTC system employing two STTCs with four transmit and receive antennas, the layered receiver with whitening process obtains a 5 dB gain over the coded layered space-time processing in the fast flat Rayleigh fading channel at the FER of 10-2.

In this paper, we propose an autonomously distributed QoS control method for MPEG video streaming in a wide area network. The capacity of the links and the characteristics of video streams change dynamically. However, managing the condition of all the links and streams in the network is difficult. In the proposed method, the routers in the network monitor the conditions of the links and streams locally and control the transmission rate of the stream server. Picture-quality oriented fairness is achieved by reducing the transmission rate of the streams with the higher PSNR in the bottleneck link. The computer simulation results show that the proposed method can be applied to a wide area network.

This paper presents a dual-frequency microstrip antenna for both 2 GHz and 5 GHz for a dual-band receiver. For a simple structure and low cost design, the microstrip feed circuit is designed on the same substrate as the antenna elements. Each antenna element is directly fed by the microstrip line, and the open stubs are loaded on the feed line of 2 GHz to suppress the higher order mode resonances between 2 GHz and 5 GHz. The feed line length of each antenna is adjusted so as to change it to the open condition at the other element frequency at the feed point. In addition, we propose the antenna structure in which two antenna elements for 2 GHz are split and placed at either sides of the 5 GHz antenna to coincide with the center positions of each antenna element. We investigate the proposed antenna by calculations and measurements to show the combiner free design for the dual band antenna.

This paper introduces an efficient affine projection algorithm (APA) using iterative hyperplane projection. The inherent effectiveness against the rank deficient problem has led APA to be the preferred algorithm to be employed for various applications over other variety of fast converging adaptation algorithms. However, the amount of complexity of the conventional APA could not be negligible because of the accomplishment of sample matrix inversion (SMI). Another issue is that the "shifting invariance property," which is typically exploited for single channel case, does not hold ground for space-time decision-directed equalizer (STDE) application deployed in single-input-multi-output (SIMO) systems. Therefore, fast adaptation schemes, such as fast traversal filter based APA (FTF-APA), becomes impossible to utilize. The motivation of this paper deliberates on finding an effective algorithm on the basis of APA, which yields low complexity while sustaining fast convergence as well as excellent tracking ability. The performance of the proposed method is evaluated under wireless SIMO channel in respect to bit error rate (BER) behavior and computational complexity, and upon completion, the validity is confirmed. The performance of the proposed method is evaluated under wireless SIMO channel in respect to bit error rate (BER) behavior and computational complexity, and upon completion, the validity is confirmed.

Some plants have air purification ability. This purification ability of plants is considered a promising method for indoor air purification because of the low cost and high purification performance. Therefore, several studies have been carried out to investigate the relationship between the air purification ability of plants and environmental conditions. Nevertheless, the purification mechanism and process have not been clarified yet. In this paper, we investigated the air purification process in plants by bioelectrical potential analysis using linear and nonlinear analysis methods. First, we showed that two types of plants have a high air purification ability; Schefflera and Boston fern. Next, we measured AC bioelectrical potential during the purifying process of plants for pollutant gas. Then, we evaluated the power spectra of time series data of the bioelectrical potential. We found that the power spectra shifted to a lower level after gas injection over all frequencies. Thus, the higher power spectrum came from possible higher physiological activities of the plant. Finally, we introduced a nonlinear analysis method from the dynamical system theory. We transformed the time series data of the potential to a higher dimensional state space using a delay coordinate, which is often used in the field of nonlinear time series analysis. The results show that the orbits in the reconstructed state space have a large variation in gas injection. These experimental results suggest that the measurement of bioelectrical potential could become a useful method for evaluating the air purification ability of plants.

With the need and adoption of link aggregation where multiple links exist between two adjacent nodes in order to increase transmission capacity between them, there arise the problems of service guarantee and fair sharing of multiple servers. Although a lot of significant work has been done for single-server scheduling disciplines in the past years, not much work is available for multi-server scheduling disciplines. In this paper, we present and investigate two round robin based multi-server scheduling disciplines, which are Multi-Server Uniform Round Robin (MS-URR) and Multi-Server Deficit Round Robin (MS-DRR). In particular, we analyze their service guarantees and fairness bounds. In addition, we discuss the misordering problem with MS-DRR and present a bound for its misordering probability.

This letter describes the current mechanism for IP address configuration in the wireless Internet and examines its drawbacks, and suggests a new mechanism of address configuration which provides a reduced message exchange for address configuration in the wireless Internet over the current 4-way message exchange when performing address configuration through DHCP. Analytic performance evaluation and comparison have shown that the proposed mechanism is faster in terms of delay than the existing mechanism including reduced packet loss when in motion.

An adaptive interpolated FIR (IFIR) echo canceller was recently proposed for xDSL applications. This canceller consists of an FIR filter, an IFIR filter, and a tap-weight overlapping and nulling scheme. The FIR filter is used to cancel the short and rapidly changing head echo while the IFIR filter is used to cancel the long and slowly decaying tail echo. This echo canceller, which inherits the stable characteristics of the conventional FIR filter, requires low computational complexity. It is well known that the interpolation filter for an IFIR filter has great influence on the interpolated result. In this paper, a least-squares method is proposed to obtain optimal interpolation filters such that the performance of the IFIR echo canceller can be further improved. Simulations with a wide variety of loop topologies show that the optimal IFIR echo canceller can effectively cancel the echo up to 73.0 dB (for an SHDSL system). About 57% complexity reduction can be achieved compared to a conventional FIR filter.

The effects of air-intake format of forced-air-cooled equipment on the efficiency of air conditioning systems are studied. A modern data center features a large number of information-processing devices to provide telecommunication services. These devices generate considerable heat, and the equipment that houses these devices often employs "forced air cooling" in which a cooling effect is achieved by sucking in large amounts of room air. An air conditioning system used for a machine room filled with such equipment therefore requires high fan driving power resulting in significantly low air conditioning efficiency. In this study, we first performed mockup-based experiments to obtain a quantitative understanding of how different air-intake formats for equipment affect the temperature at various room locations such as equipment intake. We then created a model for predicting the temperature at various locations, and on the basis of this model, we analyzed the factors affecting intake temperature and examined how intake temperature affects air conditioning efficiency. It was found that placing air inlets in the lower 1/3 portion of forced-air-cooled equipment could prevent the equipment from reabsorbing the hot air that it blows out and therefore improve air conditioning efficiency.

Discrete-time queueing models have been studied for many years because of their direct applicability in the performance evaluation of digital communication system and networks, where buffers are used to temporarily store information packets which cannot be transmitted instantaneously. In this paper, we investigate the behavior of a discrete-time multiserver buffer system with infinite buffer size. Packets arrive in the system according to a two-state correlated arrival process. The service times of the packets are assumed to be independent and identically distributed according to a geometric distribution. We present an analytical technique, based on the use of generating functions, for the analysis of the system. Explicit expressions are obtained for the mean values, the variances and the tail distributions of the system contents and the packet delay. The influence of the various model parameters on the behavior of the system is shown by means of some numerical examples.