In this letter we present steady-state analyses of a gradient algorithm (GA) for second-order adaptive infinite impulse response (IIR) notch filters. A method for deriving more accurate estimation mean square error (MSE) expressions than the recently proposed method is presented. The method is based on the estimation error power spectral density (PSD). Moreover, an expression for the estimation bias for the adaptive IIR notch filter with constrained poles and zeros is shown to be obtained from the estimation MSE expression. Simulations are presented to confirm the validity of the analyses.

In this paper we propose a chip-level receiver for optical frequency hopping code-division multiple-access (FH-OCDMA) systems. The proposed chip-level receiver for FH-OCDMA consists of an arrayed waveguide grating (AWG), and photo-detector (PD) for each mark chip, and uses the principles of the chip-level receiver. We analyze the error rate performance of the FH-OCDMA system with the proposed chip-level receiver with treating APD noise, thermal noise, and multi-user interference (MUI) using a Gaussian approximation. We compare the performance of the proposed chip-level receiver to that of the conventional correlation receiver. We show that the proposed chip-level receiver has a better bit error probability and can accommodate more users than the conventional correlation receiver.

We investigated performance improvement in a cellular system by introducing direct communication between terminals. Previous research has indicated that direct communication efficiently uses channels; however, this is not always so. We studied two factors that affect how much efficiency improves. One is the distribution of terminals. We defined some typical distributions with localization of terminals and analyzed how the difference between the distributions affected the performance improvement by direct communication. Another factor is the mobility of terminals, because mobility shortens the length of time during which terminals are directly connected. We analyzed how mobility affected performance improvement by direct communication. For the analyses, we used some theoretical techniques.

In order to improve the forward link capacity of cdma2000 HRPD (High Rate Packet Data) or CDMA2000 1xEV-DO, it is significant to overcome multi-path interference. This paper focuses on FDE (Frequency Domain Equalization) with MMSE (Minimum Mean Square Error) criterion. On top of that, backward compatibility with HRPD should be maintained, in other words common channels such as the pilot channel should not be changed. Thus, the PN (Pseudo Noise) spread pilot block without CP (Cyclic Prefix) signals has to be dealt with for FDE. However, this will cause the conventional channel estimation accuracy to deteriorate. In order to improve the estimation accuracy of the conventional method, this paper presents a MRC (Maximal Ratio Combining) spectrum estimator, IPI (Inter-Path Interference) canceller, and path searcher. The results obtained from computer simulations reveal that the proposed method can improve the PER (Packet Error Rate) performance significantly. If compared with Rake combiner and TDE (Time Domain Equalization) with NLMS (Normalized Least Mean Square) scheme, the maximum data rates at a fixed PER of 1% can be increased by 5 to 8 times and 1.25 to 2.67 times, respectively.

A distributed denial-of-service (DDoS) attack presents a very serious threat to the stability of the Internet. In a typical DDoS attack, a large number of compromised hosts are amassed to send useless packets to jam a victim or its Internet connection, or both. Defense against DDoS attacks as well as identification of their sources comprise demanding challenges in the realm of Internet security studies. In this paper, effective measures are proposed for detecting attacks in routers through the use of queuing models, which help detect attacks closer to the attack sources. Utilizing these measures, an effective DDoS attack detection and packet-filtering scheme is proposed. The suggested approach is a cooperative technique among routers intended to protect the network from persistent and severe congestion arising from a rapid increase in attack traffic. Through computer simulations, it is shown that the proposed scheme can trace attacks near to the attack sources, and can effectively filter attack packets.

The EDD connection admission control scheme has been proposed for supporting real-time communication in packet-switched networks. In the scheme, when a connection establishment request occurs, the worst-case link delay in each link along the connection is calculated to determine whether the request can be accepted or not. In order to calculate the worst-case link delay, we must perform a check called the point schedulability check for each of some discrete time instants (checkpoints). Therefore when there are many checkpoints, the worst-case link delay calculation is time-consuming. We have proposed a high-speed calculation method. The method finds some checkpoints for which the point schedulability check need not be performed and removes such unnecessary checkpoints in advance before a connection establishment request occurs, and the check is performed for each of the remaining checkpoints after the request occurs. However, the method is not so effective under the situation that the maximum packet length in networks is large, because the method can find few unnecessary checkpoints under the situation. This paper proposes a new high-speed calculation method. We relax the condition which determines whether or not the point schedulability check need not be performed for each checkpoint in our previous method and derive a new condition for finding unnecessary checkpoints. Using the proposed method based on the new condition, we can increase the number of unnecessary checkpoints compared to our previous method. Numerical examples which are obtained by extensive simulation show that the proposed method can attain as much as about 50 times speedup.

An atmospheric visibility measurement system capable of quantifying the most common operating range of onboard exteroceptive sensors is a key parameter in the creation of driving assistance systems. This information is then utilized to adapt sensor operations and processing or to alert the driver that the onboard assistance system is momentarily inoperative. Moreover, a system capable of either detecting the presence of fog or estimating visibility distances constitutes in itself a driving aid. In this paper, we first present a review of different optical sensors likely to measure the visibility distance. We then present our stereovision based technique to estimate what we call the "mobilized visibility distance". This is the distance to the most distant object on the road surface having a contrast above 5%. In fact, this definition is very close to the definition of the meteorological visibility distance proposed by the International Commission on Illumination (CIE). The method combines the computation of both a depth map of the vehicle environment using the "v-disparity" approach and of local contrasts above 5%. Both methods are described separately. Then, their combination is detailed. A qualitative evaluation is done using different video sequences. Finally, a static quantitative evaluation is also performed thanks to reference targets installed on a dedicated test site.

We present room temperature current voltage characteristics from SiGe interband tunneling diodes epitaxially grown on highly resistive Si(001) substrates. In this case, a maximum peak to valley current ratio (PVCR) of 5.65 was obtained. The possible integration of a SiGe tunnel diode with a strained Si transistor lead us to investigate the growth of SiGe interband tunneling diodes on Si0.7Ge0.3 virtual substrates. A careful optimization of the layer structure leads to a maximum PVCR of 1.36 at room temperature. The latter value can be further increased to 2.26 at 3.7 K. Our results demonstrate that high quality SiGe interband tunneling diodes can be realized, which is of great interest for future memory and high speed applications.

This paper proposes a novel image processing method based on a percolation model. The percolation model is used to represent the natural phenomenon of the permeation of liquid. The percolation takes into account the connectivity among the neighborhoods. In the proposed method, a cluster formation by the percolation process is performed first. Then, feature extraction from the cluster is carried out. Therefore, this method is a type of scalable window processing for realizing a robust and flexible feature extraction. The effectiveness of proposed method was verified by experiments on crack detection, noise reduction, and edge detection.

In order to reduce the traffic load and improve the system's lifetime, a cluster-based routing protocol has attracted more attention. In cluster-based sensor networks, energy can be conserved by combining redundant data from nearby sensors into cluster head nodes before forwarding the data to the destination. The lifespan of the whole network can also be expanded by the clustering of sensor nodes and through data aggregation. In this paper, we propose a cluster-based routing protocol which uses the location information of sensors to assist in network clustering. Our protocol partitions the entire network into several clusters by a particle swarm optimization (PSO) clustering algorithm. In each cluster, a cluster head is selected to deal with data aggregation or compression of nearby sensor nodes. For this clustering technique, the correct selection of the number of clusters is challenging and important. To cope with this issue, an energy dissipation model is used in our protocol to automatically estimate the optimal number of clusters. Several variations of PSO-clustering algorithm are proposed to improve the performance of our protocol. Simulation results show that the performance of our protocol is better than other protocols.

This letter proposes a peak power reduction method that optimizes sub-carrier phases of an OFDM signal. The proposed method doesn't require side information transmission and original signal regeneration, which are required in conventional peak power reduction methods with phase optimization, since the optimized phases are distributed as jitter around the original phases before optimization. The iterative PTS (partial transmit sequences) algorithm with a restricted phase control range is used for the jitter injection: the phase optimization process is repeated with widening the control range. A computer simulation is carried out to estimate the proposed method performance. The results show that the proposed method can reduce the peak power by 4 dB when the power penalty caused by phase jitter is only 0.2 dB.

In order to efficiently mitigate emissions radiated from electrical equipment, emission source visualization methods need to be studied. In this paper, we propose a new macroscopic visualization method based on an optimization process which uses only cylindrically-scanned electric field amplitude data from an EMI test facility as specified by CISPR, and so does not need a special measurement system. The presented method divides the visualization space into three-dimensional rectangular cells, and estimated current values through the optimization process are sorted into each corresponding cell. By displaying the summed value of every cell, the emission source can be visualized. For this study, the spatial resolution was evaluated by computer simulation, with a result of around 0.2 m using a cell size of 0.1 m. With subsequent experimental verification using a comb generator in a semi-anechoic chamber, the visualization deviation was found to be less than 0.1 m in a frequency range of 100 MHz to 800 MHz. When two spherical dipole antennas were used, the deviation was less than 0.15 m. Finally, visualization results from a facsimile unit and a PC as real EUTs were shown and basic applicability of this method demonstrated.

Experimental result and theoretical analysis are reported for bias-voltage dependence of oscillation frequency in resonant tunneling diodes (RTDs) integrated with slot antennas. Frequency change of 18 GHz is obtained experimentally for a device with the central oscillation frequency of 470 GHz. The observed frequency change is attributed to the bias-voltage dependence of the transit time of electrons across the RTD layers, which results in a voltage-dependent capacitance added to RTD. Theoretical analysis taking into account this transit time is in reasonable agreement with the observed results. Voltage-controlled RTD oscillators in the terahertz range are expected from the theoretical results. A structure suitable for large frequency change is also discussed briefly.

An active integrated antenna (AIA) oscillator consisting of an active circuit and planar antenna on the same substrate can be used as a high-performance, low-cost, small component for millimeter-to-sub-millimeter wave applications. We describe a highly extended, finite-difference-time-domain full-wave analysis method for designing AIA circuits precisely. It treats active devices as distributed elements. Using this method and 0.1-µm-gate InP-based HEMTs, we fabricated W-band AIA oscillators with an oscillation frequency of 111 GHz.

In this letter, a method estimating the intercell carrier frequency-offset (CFO) in orthogonal frequency division multiplexing (OFDM)-based cellular systems is proposed for the user's equipment (UE), especially at the cell boundary, in downlink channels. After describing a new method of deriving the intercell CFO from the signals received by adjacent base stations (BSs), we propose a cell-searching method using the estimated CFOs. It is shown by computer simulation that the proposed methods can uniquely estimate the intercell CFOs and identify the target BS with a high detection probability at the UE.

In an effort to reduce switch cost, we present the optimum numbers of tunable wavelength converters (TWCs) and internal wavelengths required for contention resolution of asynchronous and variable length packets, in the optical packet switch (OPS) with the shared fiber delay line (FDL) buffer. To optimize TWCs and internal wavelengths related to OPS design cost, we proposed a scheduling algorithm for the limited TWCs and internal wavelengths. For three TWC alternatives (not shared, partially shared, and fully shared cases), the optimum numbers of TWCs and internal wavelengths to guarantee minimum packet loss are evaluated to prevent resource waste. Under a given load, TWCs and internal wavelengths could be significantly reduced, guaranteeing the same packet loss as the performance of an OPS with full TWCs and internal wavelengths.

A novel dual band transmitter module for 2.4 GHz and 5.8 GHz wireless LAN applications with adaptive digital predistortion linearization is presented. The module operates either as a power amplifier for 2.4 GHz or frequency doubler for 5.8 GHz band. Amplification gain is 12.9 dB at 2.4 GHz and multiplication gain is 3.3 dB at 5.8 GHz. At 2.4 GHz band, the second harmonic is about 36.5 dB lower than the fundamental, and the 2.9 GHz fundamental signal is 20.3 dB lower than the second harmonic output at 5.8 GHz operation. An adaptive digital predistortion scheme is proposed to linearize the 2.4 GHz amplifier, and to get the proper 5.8 GHz band wireless LAN signal. The 2.4 GHz amplifier with predistortion satisfies the ACPR mask requirement for the input 1 dB compression power of 5 dBm and the linearized frequency doubler shows 26 dB ACPR improvement at 11 MHz offset from center frequency by using the proposed predistortion linearization. The frequency doubler output spectrum with predistortion does meet the IEEE standard Tx mask.

Experimental investigations on detection of terahertz radiation are presented. We used plasma wave instability phenomenon in nanometer Silicon field effect transistor. A 30 nm gate length transistor was illuminated by THz radiation at room temperature. We observe a maximum signal near to the threshold voltage. This result clearly demonstrates the possibility of plasma wave THz operation of these nanometer scale devices. The response was attributed to a non resonant detection. We also demonstrate the possibility to observe a resonant detection on the same devices.

Point pattern matching (PPM) arises in areas such as pattern recognition, digital video processing and computer vision. In this study, a novel Genetic Algorithm (GA) based method for matching affine-related point sets is described. Most common techniques for solving the PPM problem, consist in determining the correspondence between points localized spatially within two sets and then find the proper transformation parameters, using a set of equations. In this paper, we use this fact that the correspondence and transformation matrices are two unitary polar factors of Grammian matrices. We estimate one of these factors by the GA's population and then evaluate this estimation by computing an error function using another factor. This approach is an easily implemented one and because of using the GA in it, its computational complexity is lower than other known methods. Simulation results on synthetic and real point patterns with varying amount of noise, confirm that the algorithm is very effective.

In this paper, a new stereo line segment matching algorithm is presented. The main purpose of this algorithm is to increase efficiency, i.e. increasing the number of correctly matched lines while avoiding the increase of mismatches. In this regard, the reasons for the elimination of correct matches as well as the existence of the erroneous ones in some existing algorithms have been investigated. An attempt was also made to make efficient uses of the photometric, geometric and structural information through the introduction of new constraints, criteria, and procedures. Hence, in the candidate determination stage of the designed algorithm two new constraints, in addition to the reliable epipolar, maximum and minimum disparity and orientation similarity constraints were employed. In the process of disambiguation and final matches selection, being the main problem of the matching issue, regarding the employed constraints, criterion function and its optimization, it is a completely new development. The algorithm was applied to the images of several indoor scenes and its high efficiency illustrated by correct matching of 96% of the line segments with no mismatches.