Voice over Internet protocol (VoIP) is to transfer voice packets over IP networks, while voice signal is processed by using digital signal processing technology before being transmitted. VoIP quality cannot be expected, because it is hard to predict the influence of delay, packet loss rate, packet error, etc. It is difficult to rebuild the voice wave form, if a large amount of voice packets are lost. This paper mainly studies on how to maintain a better voice quality over hybrid fiber/coaxial (HFC) networks, if it is inevitable to drop packets. We particularly consider the data over cable service interface specification (DOCSIS) version 1.1 with the unsolicited grant service with activity detection (UGS/AD) for VoIP services. We propose a smallest successive times first (SSTF) scheduling algorithm to schedule VoIP packets for cable modem termination system (CMTS), which can support fair transmission and long-term transmission continuity for VoIP connections. We analyze voice quality about continuity of the transmitted VoIP packets, consecutive clipping times, and VoIP packet drop rate for all connections. Performance measurement shows excellent results for the proposed algorithm by simulation experiments and objective evaluation.

In this paper, we consider a blind channel estimation and equalization for single input multiple output (SIMO) channels. It is based on the one-step forward multichannel linear prediction error method. The derivation of the existing method is based on the noiseless assumption, however, we analyze the effects of additive noise at the output of the one-step forward multichannel linear prediction error filters. Moreover, we derive analytical results for the error in the blind channel estimation and equalization using linear prediction.

Direct digital frequency synthesizers (DDFS) provide fast frequency switching with high spectral purity and are widely used in modern spread spectrum wireless communication systems. ROM-based DDFS uses a ROM lookup table to store the amplitude of a sine wave. A large ROM table is required for high spectral purity. However, a larger ROM uses more area and consumes more power. Several ROM compression methods, including Sunderland technique based on simple trigonometric identities and quantization & error compensation techniques, have been reported. In this paper, we suggest several new techniques to reduce the ROM size. One new technique uses more number of hierarchical levels in ROM structures. Another technique uses simple interpolation techniques combined with hierarchical ROM structures. Experimental results show that the new proposed techniques can reduce the required ROM size up to 24%, when compared to that of a resent approach.

This paper provides a computational method to construct a Lyapunov function to prove a stability of hybrid automata that can have nonlinear vector fields. Algebraic inequalities and equations are formulated, which are solved via LMI optimization. Numerical examples are presented to illustrate the proposed method.

Some conventional beamformers require the direction of the desired signal. The performance of such beamformers can substantially be degraded even in the presence of small error on the directional information. In this letter, we propose a prefilter-type beamforming scheme robust to directional error by employing a simple compensator. The performance of the proposed scheme is verified by computer simulation.

This paper presents circuit techniques using pulse-width and pulse-phase modulation (PWM/PPM) approaches for VLSI implementation of nonlinear dynamical systems. The proposed circuits implement discrete-time continuous-state dynamics by means of analog processing in a time domain, and also approximately implement continuous-time dynamics. Arbitrary nonlinear transformation functions are generated by the process in which a PPM signal samples a voltage or current source whose waveform in the time domain has the same shape as the desired transformation function. Because a shared arbitrary nonlinear voltage or current waveform generator can be constructed by digital circuits and D/A converters, high flexibility and real-time controllability are achieved. By using one of these new techniques, we have designed and fabricated a CMOS chaos circuit with arbitrary 1-D maps using a 0.6 µm CMOS process, and demonstrate from the experimental results that the new chaos circuit successfully generated various chaos with 7.5-7.8 bit precision by using logistic, tent and chaotic-neuron maps.

In this paper we study the large deviation property for chaotic binary sequences generated by one-dimensional maps displaying chaos and thresholds functions. We deal with the case when nonlinear maps are the r-adic maps. The large deviation theory for dynamical systems is useful for investigating this problem.

This paper presents a simple learning algorithm for network formation. The algorithm is based on self-organizing maps with growing cell structures and can adapt input data which correspond to nodes of the network. In basic numerical experiments, as a parameter is selected suitably, our algorithm can generate network having small-world-like structure. Such network structure appears in some natural networks and has advantages in practical systems.

This paper proposes a bandwidth allocation algorithm and a demand accommodation algorithm guaranteeing utility max-min fairness under bandwidth constraints. We prove that the proposed algorithms can fairly split network resources among connections and achieve call admission control considering the fairness among different types of applications. We then formulate three different network design problems to maximize the total utility of all customers, the number of users accommodated in the network, and the average utility of the customers accommodated in the network. To solve the problems, we extend the conventional network design algorithms considering utility max-min fair share, and numerically evaluate and compare their performance. Finally, we summarize the best algorithms to design the utility max-min fair share networks considering the operation policy of network providers.

This paper presents a new template matching method based on marker-controlled watershed segmentation (TMCWS). It is applied to recognize numbers on special metal plates in production lines where traditional image recognition methods do not work well. TMCWS is a shape based matching method that uses different pattern images and their corresponding marker images as probes to explore a gradient space of an unknown image to determine which pattern best matches a target object in it. Different from other matching algorithms, TMCWS firstly creates a marker image for each pattern, and then takes both the pattern image and its corresponding marker image as a template window and shifts this window across a gradient space pixel by pixel to do a search. At each position, the marker image is used to try to extract the contour of the target object with the help of marker-controlled watershed segmentation, and the pattern image is employed to evaluate the extracted shape in each trial. All of the pattern images and their corresponding marker images are tried and the pattern that best matches the target object is the recognition result. TMCWS contains shape extraction procedures and it is a high-level template matching method. Experiments are performed with this method on nearly 400 images of metal plates and the test results show its effectiveness in recognizing numbers in noisy images.

This paper proposes and theoretically evaluates two different schemes of code acquisition for pulse-position modulation (PPM) and overlapping PPM (OPPM) fiber-optic code-division multiple-access (CDMA) systems, namely threshold-based and demodulator-based code acquisition. Single-dwell detector and serial-search algorithm are employed for both schemes. Theoretical analysis is carried out for shot-noise-limited photon-counting receiver. Discussions upon effects of various parameter settings on the performance of code acquisition for PPM/OPPM fiber-optic CDMA systems, such as index of overlap, PPM/OPPM multiplicity, average photon counts per information nat, and darkcurrents, are presented. It is shown that when the threshold is properly selected, the threshold-based code acquisition system offers better performance, in terms of mean number of training frames, than the demodulator-based one.

We investigate the effects of DoS (Denial of Service) attacks in wireless ad hoc networks using simulations, concentrating on the problem of energy availability. Our results show that the damages due to the DoS attack may quite different with those in wired networks: First, the nodes along the transmission route mostly suffer damages rather than the victim node itself. Second, if the mobile nodes are crowded and close together, the damage becomes more severe. Lastly, if the nodes have random mobility, the attacker itself consumes more energy.

We design a DAB system using space-time coding for reliable transmission in the multipath fading channel. This letter assess the performance evaluation of space-time coded DAB system. For channel estimation in the space-time coded DAB system, we introduce two training sequences and derive the mean square error of each training sequence. We then represent the average symbol error rate of the space-time coded DAB system for the specific cases of two, three, four transmit antennas.

We have proposed and theoretically verified a 2R (reshaping and regeneration) limiter circuit using continuous wave (CW) holding beam for cross-gain modulation (XGM) wavelength converter, through simulation. The gain clamping effect of semiconductor optical amplifier (SOA), which is caused by CW holding beam injected into SOA, was used to obtain the accurate optical gain and phase conditions for SOA's in 2R limiter circuit. XGM wavelength converter with the proposed 2R limiter circuit provides higher extinction ratio (ER) as well as more enhanced operation speed than any other wavelength converter. Our numerical results show that after the wavelength-converted signal from XGM wavelength converter passed the 2R limiter circuit, it was re-inverted with the improved ER of 30 dB at 5 Gb/s. In case of high-speed operation, great enhancement to decrease power penalty of about 12 dB was shown at 10 Gb/s.

In mobile cellular networks it is crucial to be able to use the available radio spectrum as efficiently as possible while providing a certain level of Quality of Service (QoS) for the users. Emergence of miscellaneous services has dramatically increased the complexity of this problem by creating a heterogeneous traffic environment. In this paper an efficient resource allocation scheme between two real-time services with different bandwidth requirements has been proposed for cellular networks with multimedia offered traffic and highly mobile users, which combines classical intera-cell resource borrowing concept with a novel inter-cell resource-sharing scheme between diverse classes of traffic. By assuming the heterogeneous offered traffic to be a combination of audio and video traffic types, through extensive simulations it will be shown that HCBA-UCB is capable of significantly improving audio teletraffic performance of the system while preserving fairness in service provision, i.e. without imposing additional expenses upon video QoS performance.

We show that the necessary and sufficient condition for the existence of a balanced bowtie decomposition of the symmetric complete multi-digraph is n 5 and λ(n-1) 0 (mod 6). Decomposition algorithms are also given.

This paper proposes a method to detect buildings and houses whose walls are not parallel to Synthetic Aperture Radar (SAR) flight path. Experimental observations show that it is difficult to detect these targets because of small backscattering characteristics. The detection method is based on the correlation coefficient in the circular polarization basis, taking full advantage of Polarimetric SAR (POLSAR) data. Since the correlation coefficient is real-valued for natural distributed targets with reflection symmetry and for non-natural targets orthogonal to illumination direction, and it becomes a complex number for non-natural targets aligned not orthogonal to radar Line-Of-Sight (LOS), the value seems to be an effective index for detection of obliquely aligned non-natural targets. The detection results are shown using the X-band Polarimetric and Interferometric SAR (Pi-SAR) single-path data set in conjunction with other polarimetric indices.

In this paper, a novel CMOS defuzzification circuit using dual-output current conveyors (DO-CCII) is introduced. The behaviour of the proposed circuit has been verified with PSPICE using the models for 1.2 µm MIETEC CMOS process. The proposed circuit offers high-speed operation and high accuracy because of using second generation current conveyors (CCII). The designed circuit is suitable for fuzzy logic controllers using center of gravity (COG) defuzzification method.

This paper theoretically evaluates the performance of overlapping pulse-position modulation (OPPM) fiber-optic code-division multiple-access (FO-CDMA) systems in the presence of code synchronization errors. The analysis is carried out with a constraint on throughput-pulsewidth product. Discussions on effects of various system parameters, such as timing offset, index of overlap, number of users, are presented. The results show that the OPPM FO-CDMA systems with high index of overlaps have better resistance against imperfect synchronization. In fact, the acceptable performance could be maintained even with timing offsets of up to 30% of chip pulsewidth. On the other hand, strict code synchronization is necessarily required, preferably within a half code chip pulsewidth.

Let G be an undirected graph and let Γ be its drawing on a plane. Each vertex in G has a label with a specified size. In this paper, we consider the problem of placing the maximum number of vertex labels in Γ in such a way that they do not overlap any vertices, edges or other labels. By refining several portions of the Kakoulis-Tollis algorithm for labeling graphical features, we present a heuristic algorithm for this problem. Experimental results show that our algorithm can place more labels than previous algorithms.