In the letter we extend our previous work, which applies genetic programming to passive filter synthesis tasks. The extended method deals with the tolerance design considerations. Experimental results show that our method can effectively generate filters which outperform those generated by traditional methods. In addition, it provides filter designers with an effective CAD tool to manage the trade-off between manufacturing yield and circuit cost.

In this paper, we propose a voltage controlled oscillator (VCO) with up mode type Miller-integrator. The controlled voltage of this VCO can continuously change 0 V center in the positive and negative bidirection. Also, the relationship between control voltage and oscillating frequency shows the good linearity, and the calculated and the measured values agree well.

This paper proposes two different packet schedulers for IEEE 802.16e type time division duplex - orthogonal frequency division multiple access (TDD-OFDMA), which are the weighted fair scheduling (WFS) and the throughput guarantee scheduling (TGS). The performance of proposed schedulers is compared to those of some of conventional schedulers such as round robin (RR), proportional fair (PF), fast fair throughput (FFTH), and fair throughput (FTH) in terms of service coverage, effective throughput and fairness at 64 kbps and 128 kbps minimum user throughput requirements. For a relatively smaller throughput (64 kbps) requirement, the proposed schedulers increase the number of users per sector within 95% service coverage while satisfying the 1xEV-DV fairness criterion. For a relatively larger throughput (128 kbps) requirement, the proposed schedulers provide higher coverage than the PF scheduler while maintaining the same effective aggregate throughput.

In this paper, we propose a parametric model checking algorithm for a subclass of Timed Automata called Parametric Time-Interval Automata (PTIA). In a PTIA, we can specify upper- and lower-bounds of the execution time (time-interval) of each transition using parameter variables. The proposed algorithm takes two inputs, a model described in a PTIA and a property described in a PTIA accepting all invalid infinite/finite runs (called a never claim), or valid finite runs of the model. In the proposed algorithm, firstly we determinize and complement the given property PTIA if it accepts valid finite runs. Secondly, we accelerate the given model, that is, we regard all the actions that are not appeared in the given property PTIA as invisible actions and eliminate them from the model while preserving the set of visible traces and their timings. Thirdly, we construct a parallel composition of the model and the property PTIAs which is accepting all invalid runs that are accepted by the model. Finally, we perform the extension of Double Depth First Search (DDFS), which is used in the automata-theoretic approach to Linear-time Temporal Logic (LTL) model checking, to derive the weakest parameter condition in order that the given model never executes the invalid runs specified by the given property.

Recently, it has been shown that the received signal in the orthogonal frequency-division multiplexing (OFDM) systems can be viewed as the synchronous code-division multiple access (SCDMA) signal in receiver after some mathematical manipulation, and the ICI term in the OFDM system is equivalent to the multiple access interference (MAI) term in SCDMA system. They proposed a successive interference cancellation multicarrier detector and it performs better than the conventional single-carrier detection schemes. To further improve the performance of OFDM systems in the presence of ICI, we propose to use a soft-in soft-out (SISO) multicarrier detector and a SISO convolutional decoder in an iterative (turbo) way. Note that full-complexity turbo multicarrier detector and turbo decoder are not used to strike a balance between performance and complexity of OFDM systems. And the transmitter structure of OFDM systems is unchanged. The simulation results show that the first iteration of the proposed scheme demonstrates 2-3 dB gain compared to the previous multicarrier detection schemes. The second and third iterations improve the performance further.

This paper proposes a new detection ordering scheme, which minimizes average error rate of the MIMO system with per antenna rate control. This paper shows an optimal scheme minimizing average error rate expressed by the Q function, and simplifies the optimal scheme by using the minimum equivalent SINR scaled by modulation indices, based on approximated error rate. In spite of reduced complexity, the simplified scheme demonstrates the almost same performance as the optimal scheme. Owing to the diversity of detection ordering, the proposed scheme has over 2 dB higher SNR gain at the BER of 10-3 than the existing ordering schemes in balanced array size systems.

This paper presents a Fault-Tolerant Object Group (FTOG) model that provides the group management service and the fault-tolerance service for consistency maintenance and state transparency. Through Intelligent Home Network Simulator, we verify that FTOG model supports both of reliability and the stability of the distributed system.

In this letter, a joint estimation algorithm of Doppler spread and frequency offset for OFDM systems in Rayleigh fading channels is proposed based on the autocorrelation function between the last part of the received OFDM signal and its copy in guard interval. It is shown by computer simulations that the proposed algorithm performs well for different Doppler spread values and carrier frequency offsets.

Congestion control in the Internet consists of two main components: the TCP Additive-Increase Multiplicative-Decrease (AIMD) mechanism on sending windows implemented by end-users, and the Active Queue Management (AQM) scheme implemented in the routers which improves the effectiveness of congestion control. TCP connection is regarded as a feedback control system. Comparably, AQM is classified as a flow controller. There are several kinds of time delays in the network, such as propagation delay, queuing delay in the buffer of the router, etc. The time delays cause degradation of performance and instability of the network. A Smith Predictor is commonly used in feedback control of plants with significant time delays to implement effective compensation. In this paper, a Smith Predictor-based PI-controller for AQM (SPPA) is proposed, which uses a TCP reference model and an average Round-Trip Time (RTT) to reduce unfavorable effects of time delays in TCP networks. The drop probability is calculated by a Proportional-Integral (PI) controller based on the prediction error. When a mismatch exists in between the actual model of the TCP process and the reference model employed by the SPPA, we demonstrate conditions under which the network is stable. The performance, robustness and effectiveness of the proposed SPPA are all evaluated using simulations. The performance of the SPPA is compared with some typical AQMs, such as the Adaptive RED, the PI-controller, and the Proportional-Differential (PD) controller.

This paper deals with new fuzzy controller for handling systems having large dead time and nonlinearities, via approximations of large rule fuzzy logic controller by simplest fuzzy controller (4 rules). The error between large rule fuzzy controller and simplest fuzzy controller are compensated by proposed compensating factors. These compensating factors are modified to handle large dead time and nonlinear systems. Features of proposed approximations are discussed. The concept of variation of nonlinearity factor of fuzzy controller is also discussed. Various processes from different literatures are utilized to demonstrate the proposed methodology. After doing many simulations it has been found that with proper tuning, overall system handles large dead time and nonlinearity which may be difficult by conventional methods. The processes are also simulated for load disturbances and change of operating point (set point) and it has been found that proposed scheme is robust for long dead times.

We propose a new class of binary nonlinear codes of constant weights derived from a permutation representation of a group that is given by a combinatorial definition such as Cayley graphs of a group. These codes are constructed by the following direct interpretation method from a group: (1) take one discrete group whose elements are defined by generators and their relations, such as those in the form of Cayley graphs; and (2) embedding the group into a binary space using some of their permutation representations by providing the generators with realization of permutations of some terms. The proposed codes are endowed with some good characteristics as follows: (a) we can easily learn information about the distances of the obtained codes, and moreover, (b) we can establish a decoding method for them that can correct random errors whose distances from code words are less than half of the minimum distances achieved using only parity checking procedures.

In this paper we are concerned with designing an extremum seeking control law for nonlinear systems. This is a modification of a standard extremum seeking controller. It is equipped with an accelerator to the original one aimed at achieving the maximum operating point more rapidly. This accelerator is designed by making use of a polynomial identification of an uncertain output map, the Butterworth filter to smoothen the control, and analog-digital converters. Numerical experiments show how this modified approach can be well in control of the Monod model of bioreactors.

In this paper, we propose a broadband 3-dB rat-race ring coupler that uses tightly coupled lines. An aperture compensation technique that can simplify the fabrication of tightly coupled lines, is also discussed here. The effective bandwidth of the proposed rat-race coupler with a return loss better than -20 dB can be increased by 14.3%, in comparison with that of March's. Its isolation is always below -20 dB and the phase shift errors less than 6.

We propose and demonstrate a novel ladder interferometric filter that exhibits flat-topped spectral response for use in wavelength-division-multiplexing (WDM) based photonic networks. We numerically analyze the flattened spectral response in a ladder-type filter by modifying the transfer matrix of ladder interferometer. Conventional parabolic-shaped and flat-topped-designed ladder interferometric filters are fabricated, and characterized. We demonstrate a flat-topped filter response in the fabricated device. The shape factor, which is defined by the ratio of -1 dB bandwidth to -10 dB bandwidth, is improved from 0.32 to 0.54. The tunability and the increase in filter extinction ratio of the proposed device are also discussed.

Faults in computer systems can occur due to a variety of reasons. These include internal effects such as coupling and external effects such as alpha particles. As we move towards smaller manufacturing technologies, the probability of errors for a single transistor is likely to increase. Even if this probability remains the same, the probability of a fault in a processor will increase linearly with the boost in the number of transistors per chip. In many systems, an error has a binary effect, i.e., the output is either correct or erroneous. However, networking systems exhibit different properties. For example, although a portion of the code behaves incorrectly due to a fault, the application can still work correctly. Therefore, measuring the effects of faults on the network processor applications require new measurement metrics to be developed. Particularly, hardware faults need to be measured in the context of their effect on the application behavior. In this paper, we highlight essential application properties and data structures that can be used to measure the error behavior of network processors. Using these metrics, we study the error behavior of seven representative networking applications under different cache access fault probabilities. With this study, we hope to bridge the gap between the circuit-level phenomena and their impact on the application behavior.

Direction-of-arrival (DOA) estimation based on subspace methods has collected much interest over a few decades, and adaptive DOA estimation with rapidly changing parameters will be necessary for wireless communications. This paper is concerned with a new subspace tracking scheme by using an accelerated LMS and RLS algorithms for time-varying parameters. The proposed accelerated adaptive algorithms are based on the internal model principle by approximately expressing the changing parameters by an expansion of polynomial time functions. Thus its application to DOA estimation based on the MUSIC and MODE schemes is presented and the effectiveness is validated in numerical simulations.

The emergence of intelligent and sophisticated attack techniques makes web services more vulnerable than ever which are becoming an important business tool in e-commerce. Many techniques have been proposed to remove the security vulnerabilities, yet have limitations. This paper proposes an adaptive mechanism for a web-server intrusion-tolerant system (WITS) to prevent unknown patterns of attacks by adapting known attack patterns. SYN flooding attacks and their adaptive defense mechanisms are simulated as a case study to evaluate the performance of the proposed adaptation mechanism.

In this paper, we propose a novel array antenna-assisted adaptive modulation scheme for fast fading environments. Although adaptive modulation is an efficient technique capable of establishing high bit-rate digital transmission in a multi-path fading environment, it is sensitive to the fast time variation of the channel because of difficulties in tracking the channel state. To resolve this problem, an array antenna-based Doppler spread compensator was applied to the adaptive modulation scheme. Computer simulation results indicated that the proposed scheme can markedly improve the bit error rate and throughput performance for the region in which the maximum Doppler frequency normalized by the packet length is up to 0.1.

This paper proposes an adaptive noise canceller (ANC) with low signal-distortion for human-robot communication. The proposed ANC has two sets of adaptive filters for noise and crosstalk; namely, main filters (MFs) and subfilters (SFs) connected in parallel thereto. To reduce signal-distortion in the output, the stepsizes for coefficient adaptation in the MFs are controlled according to estimated signal-to-noise ratios (SNRs) of the input signals. This SNR estimation is carried out using SF output signals. The stepsizes in the SFs are determined based on the ratio of the primary and the reference input signals to cope with a wider range of SNRs. This ratio is used as a rough estimate of the input signal SNR at the primary input. Computer simulation results using TV sound and human voice recorded in a carpeted room show that the proposed ANC reduces both residual noise and signal-distortion by as much as 20 dB compared to the conventional ANC. Evaluation in speech recognition with this ANC reveals that with a realistic TV sound level, as good recognition rate as in the noise-free condition is achieved.

This paper describes two way satellite system environments on geostationary orbit (GEO) and performance enhancement mechanisms which reduces round trip time (RTT) and supports real-time services. We use performance enhancing proxy (PEP) for reducing round trip time and user-level real-time scheduler for reducing deadline violation tasks. The user-level real-time scheduling method classifies priority of user process into four types and those are reflected in kernel. With these dual performance enhancement mechanisms, we can improve quality of service (QoS) of end-user who connects to the DVB-RCS system.