The minimum initial marking problem MIM of Petri nets is described as follows: "Given a Petri net and a firing count vector X, find an initial marking M0, with the minimum total token number, for which there is a sequence δ of transitions such that each transition t appears exactly X(t) times in δ, the first transition is enabled at M0 and the rest can be fired one by one subsequently." This paper proposes two heuristic algorithms AAD and AMIM + and shows the following (1) and (2) through experimental results: (1) AAD is more capable than any other known algorithm; (2) AMIM + can produce M0, with a small number of tokens, even if other algorithms are too slow to compute M0 as the size of an input instance gets very large.

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.

This letter introduces a modified multiband orthogonal frequency division multiplexing (MB-OFDM) signal with low peak-to-average power ratio (PAPR). From the presented results, we can see that the modified MB-OFDM signal can be implemented with low PAPR. When MB-OFDM signals is equipped with a partial transmit sequence (PTS) approach, the PAPR of the modified MB-OFDM signals using two partial transmit sequences is almost the same to that of the ordinary MB-OFDM signals using four partial transmit sequences.

In order to judge the goodness of zero correlation zone sequence sets, a new concept, called ZCZ characteristic, is proposed. Then by defining a sequence operation, i.e. correlation product, and establishing its basic properties, a new approach to construct sets of sequences with a large zero correlation zone is presented.

Quality of Service (QoS)-constrained policy has an advantage in that it satisfies QoS requirements requested by users. We propose a Quorum based resource management scheme in Grid and resource reconfiguration algorithm based on temporal execution time estimation for satisfying QoS. We compare and evaluate the processing time and deviation of the resource reconfiguration algorithm using a Heart Hemodynamics analysis.

In this letter, a novel general design method of quasi-orthogonal space-time block codes for four antennae is presented. Comparison with the design method proposed by Jafarkhani, this method enlarges the number of quasi-orthogonal space-time block codes. The performance of these codes is also analyzed and the simulation results show that it is similar to even better than that of the codes proposed by Jafarkhani.

In this paper, three new ultra wideband (UWB) communication systems with quadrature-phase shift keying (QPSK) impulse modulation are proposed. First, direct-sequence (DS) multiple-access scheme is applied. The second proposed system is based on time-hopping (TH) multiple-access scheme. The last proposed system applies TH multiple-access scheme with QPSK impulse modulation and pulse position modulation (PPM). The conventional UWB communications as TH scheme with PPM modulation and DS scheme with binary-phase shift keying (BPSK) are used to compare. The simulation results show that all proposed UWB communication systems can provide obviously better performances compared with the conventional TH-PPM and DS-BPSK UWB communication systems. The comparisons in aspects of transmission bit rate and the number of users are also investigated.

A recursive quadratic programming (RQP) approach is proposed for multiuser detection in multicarrier code-division multiple-access (MC-CDMA) systems. In this approach, the combinatorial problem associated with the optimal maximum likelihood (ML) detection is relaxed to a quadratic programming (QP) problem first and then a recursive approach is developed to improve the detection performance. Computer simulations are presented which demonstrate that the detector developed based on the proposed approach offers close-to-optimal symbol-error rate (SER) performance which outperforms several existing suboptimal detectors.

A robust joint symbol timing and fractional frequency offset estimator for OFDM systems in multipath fading channels is proposed based on cyclic shifting and autocorrelation properties of PN codes. A new timing metric is also introduced by considering the delay spread to improve the robustness of the estimator in the multipath fading channels.

This paper considers the low-frequency scattering by a circular dielectric cylinder and modifies the exact polarizability tensor to extend the valid region of the known low-frequency solution. When compared to the traditional formulation, the proposed solution is shown to be valid for cylinders with a higher dielectric constant and larger radius.

In this paper, we present a new all-digital carrier recovery loop for high-order quadrature amplitude modulation (QAM) signal constellations. The proposed approach is a blind phase-frequency detector structure that consists of a phase detector, a phase offset estimator, a frequency offset estimator, and a digital control oscillator. Compared to previous related approaches, the proposed algorithm provides a wider acquisition range and a more accurate estimation of frequency and phase offsets. These features are demonstrated by simulation results of the DOCSIS (Data-Over-Cable Service Interface Specifications) cable modem system.

Frequency-domain and time-domain novel uniform asymptotic solutions for the scattered fields by an impedance cylinder and a dielectric cylinder, with a radius of curvature sufficiently larger than the wavelength, are presented in this paper. The frequency-domain novel extended UTD and the modified UTD solutions, derived by retaining the higher-order terms in the integrals for the scattered fields, may be applied in the deep shadow region in which the conventional UTD solutions produce the substantial errors. The novel time-domain uniform asymptotic solutions are derived by applying the saddle point technique in evaluating the inverse Fourier transform. We have confirmed the accuracy and validity of the uniform asymptotic solutions both in the frequency-domain and in the time-domain by comparing those solutions with the reference solutions calculated from the eigenfunction expansion (frequency-domain) and from the hybrid eigenfunction expansion and fast Fourier transform (FFT) method (time-domain).

A sampling frequency offset estimation scheme for MB-OFDM UWB systems is proposed based on technical specification and multi-band utilization of the MB-OFDM. An estimation scheme using simple weighting factor based on the received signal power of each sub-channel is also introduced to efficiently combine estimates obtained from all the sub-carriers and to improve the estimation performance.

To take intercarrier interference (ICI) attributed to time variations of the channel into consideration, the time- and frequency-selective (doubly-selective) channel is parameterized by a finite parameter model. By capitalizing on the finite parameter model to approximate the doubly-selective channel, a Kalman filter is developed for channel estimation. The ICI suppressing, reduced-complexity Viterbi-type Maximum Likelihood (RML) equalizer is incorporated into the Kalman filter for recursive channel tracking and equalization to improve the system performance. An enhancement in the channel tracking ability is validated by theoretical analysis, and a significant improvement in BER performance using the channel estimates obtained by the recursive channel estimation method is verified by Monte-Carlo simulations.

In order to simultaneously combat both of the inter-carrier interferences (ICIs) and multiple access interferences (MAIs) to achieve reliable performance in multi-carrier code division multiple access (MC-CDMA) systems, this letter proposes a maximum likelihood based scheme for joint frequency offset estimation and multiuser symbol detection. To reduce the computational complexity called for by the joint decision statistic without extra mechanisms, the genetic algorithm (GA) is employed to solve the nonlinear optimization involved. Due to the robustness of the GA, the joint decision statistic can be efficiently solved, and, as shown by furnished simulation results, the proposed approach can offer satisfactory performance in various scenarios.

This paper describes a multiband vector quantization (VQ) technique based on inner product for wideband speech coding at 16 kb/s. Our approach consists of splitting the input speech into two separate bands and then applying an independent coding scheme for each band. A code excited linear prediction (CELP) coder is used in the lower band while a transform based coding strategy is applied in the higher band. The spectral components in the higher frequency band are represented by a set of modulated lapped transform (MLT) coefficients. The higher frequency band is divided into three subbands, and the MLT coefficients construct a vector for each subband. Specifically, for the VQ of these vectors, an inner product-based distance measure is proposed as a new strategy. The proposed 16 kb/s coder with the inner-product based distortion measure achieves better performance than the 48 kb/s ITU-T G.722 in subjective quality tests.

Missing data which inevitably occurs in observed time series may lead to an erroneous result based on the correlation integral analysis. Effects of data, missing at regular and irregular times, on the analyzed result are estimated. A model estimation is obtained for the Lorenz time series. The effects of the missing data in economic and astronomical time series are estimated using the correlation integral analysis. A convenient method of choosing a time lag is proposed to minimize the effect of regularly missing data.

This letter deals with our investigations into improving the performance of a wireless uplink system when an orthogonal frequency-division multiple access (OFDMA) is used as an access scheme. To do this, the OFDMA-based uplink system adopts a frequency diversity coupled with a cyclic time shift (CTS) at the transmitter, which is named as the FD-OFDMA system with CTS. It is found that the multi-user FD-OFDMA system equipping with CTS can decrease the probability of destroying the orthogonality among the users and provide the MAI-robust reception without decreasing the bandwidth efficiency of the system.

In software defined radio systems, placing the analog-to-digital converter (ADC) near the antenna part in the block diagram of the receiver is desired to improve the flexibility of the system. The radio frequency (RF) sampling method, in which the received signal is sampled at the RF stage, realizes such structure. The undersampling is a potential method to sample the RF signal using the existing consumer ADCs because high speed ADCs are required in the traditional methods, such as Nyquist sampling or the oversampling of the RF signal. This paper presents a technique to determine the minimum sampling frequency to undersample the separated multiple wireless systems simultaneously. In addition, this paper proposes a frequency selecting scheme that enables selection of a lower sampling frequency by receiving at least the desired transmission channels in the wireless system signals. This paper also provides a result of performance analysis of the proposed scheme.

Proportional fair bandwidth allocation in packet switches is a fundamental issue to provide quality of service (QoS) support in IP networks. In input-queued switches, packet-mode scheduling delivers all the segments of a packet contiguously from the input port to the output port, thus greatly simplifying the design of packet reassembly modules and yielding performance advantage over cell-mode scheduling under certain conditions [1]. One of the important issues of packet-mode scheduling is how to achieve fair bandwidth allocation among flows with different packet sizes. This paper presents an algorithm called packet-mode fair scheduling (pFS) that guarantees each flow a bandwidth proportional to its reservation regardless of the packet size distribution and the system load. Simulations show that our approach achieves good fairness as well as high throughput and low packet delay. Compared to algorithms without fairness mechanism, pFS yields significant performance improvement in terms of average packet delay when the traffic is heterogeneous. A hardware implementation is presented to show that the proposed algorithm has low complexity and the computation can be completed in a single clock cycle, which makes pFS applicable to high-speed switches.