We clarify the effectiveness of receiver-side compensation in offsetting fiber Bragg grating (FBG) dispersion induced-electrical signal-to-noise ratio (SNR) degradation in a 10 Gb/s 8-channel wavelength-division multiplexing (WDM) 6,400 km transmission system. The receiver-side compensation greatly improves the SNR degradation. The allowable accumulated FBG dispersion is -400 1000ps/nm for the worst arrangement, a single FBG at the transmitter, which is about half the accumulated fiber dispersion permissible with receiver-side compensation.

Studies of cellular automata (CA) based random number generators (RNGs) have focused mainly upon symmetrically connected networks with neighborhood sizes of three or five. Popular field programmable gate array configurations feature a four-input (i.e., 16-row) lookup table. Full utilization of the four-input lookup table leads to the potential for asymmetrically connected cellular automata networks with a neighborhood size of four. From each of various 1-d, 2-d, and 3-d networks with periodic boundary conditions, the 1000 highest entropy CA RNGs were selected from the set of 65,536 possible uniform (all CA truth tables the same) implementations. Each set of 1000 high-entropy CA was then submitted to Marsaglia's DIEHARD suite of random number tests. A number of 64-bit, neighbor-of-four CA-based RNGs have been discovered that pass all tests in DIEHARD without resorting to either site spacing or time spacing to improve the RNG quality.

This paper presents the transmission performance of a class-IV partial-response signaling SSB system and proposes a method that can improve its power efficiency. A line code that has no dc component has been used in the SSB transmission of digital signals. The type of line code, such as a partial-response signaling, increases the modulation states, and as a result, decreases the power efficiency. To overcome this obstacle, a new demodulation method called "re-filtering and combining" is proposed on the assumption of orthogonal phase detection. The demodulated quadrature channel is re-filtered by a Hilbert filter and is combined with the in-phase channel. It is confirmed by computer simulations that the new demodulation method improves the BER performance and a 3 dB improvement of the power efficiency is obtained.

An algorithm for augmenting a binary linear code is presented. The input to the code augmenting algorithm is (n,k,d) code C and the output is an (n,k*,d) augmented code C (k* k) satisfying C C and the Gilbert bound. The algorithm can be considered as an efficient implementation of the proof of Gilbert bound; for a given binary linear code C, the algorithm first finds a coset leader with the largest weight. If the weight of the coset leader is greater than or equal to the minimum distance of C, the coset leader is included to the basis of C.

We propose a new adaptive FEC scheme combined with ELN (Explicit Loss Notification) that was proposed for improving TCP performance in wireless cellular networks. In our method, transmission errors on the wireless link are measured at the packet level and the error status is notified the TCP sender with ELN. According to this information, an appropriate FEC code is determined in order to maximize the TCP performance. We first compare the TCP performance using Snoop Protocol, ELN and the fixed FEC, through which we find the appropriate FEC code against given BER (bit error ratio). We then show how the adaptive FEC can be realized using our solution, and also examine the appropriate observation period of measuring BER enough for the fading speed on the noisy wireless link. We finally demonstrate that our method can achieve better performance than the conventional fixed FEC by using the Gilbert model as a wireless error model.

A performance comparison is developed between a chaotic communication system and a spread spectrum system with similar features in terms of bandwidth and transceiver structure but based on more conventional Gold sequences. Comparison is made in the presence of noise and multipath contributions which degrade the channel quality. It is shown that, because of its more favourable correlation properties, the chaotic scheme exhibits lower error rates, at a parity of the bandwidth expansion factor. The same favourable correlation properties are also used to explain and show, through a numerical example, the benefits of chaotic segments in a multi-user environment.

Since any suggestion to regional services are not described in Kerberos, authentication between regions can be performed via PKINIT (Public Key Cryptography for Initial Authentication) presented by IETF (Internet Engineering Task Force) CAT working group. In this paper, an efficient Kerberos authentication mechanism associated with X.509 and Domain Name system (DNS) is presented by employing the two distinct key management systems - asymmetric and symmetric methods. A new protocol is better than the authentication mechanism proposed by IETF CAT Working group in terms of communication complexity.

This paper presents a new operation and maintenance system for PON (Passive Optical Network) subscriber loops and an assessment of its feasibility through experiments. This system adopts a broadband continuous wave light source as a testing signal and a fiber grating filter as a reflective component. The fiber grating filter is inserted somewhere in each subscriber loop for reflection of the testing signal. Our results show that the proposed system operates well for the purposes of quick decision of loop state and easy testing for PON subscriber loops.

Algorithms are presented for the four elementary arithmetic operations, to perform reliable floating-point arithmetic operations. These arithmetic operations can be achieved by applying residue techniques to the weighted number systems and performed with no accuracy lost in the process of the computing. The arithmetic operations presented can be used as elementary tools (on many existing architectures) to ensure the reliability of numerical computations. Simulation results especially for the solutions of ill-conditioned problems are given with emphasis on the practical usability of the tools.

Adaptive optimization of the notch bandwidth of a lattice-based adaptive infinite impulse response (IIR) notch filter is presented in this paper. The filter is used to improve the performance of a direct sequence spread spectrum (DSSS) binary phase shift keying (BPSK) communication system by suppressing a narrow-band interference at the receiver. A least mean square (LMS) algorithm used to adapt the notch bandwidth coefficient to its optimum value which corresponds to the maximum signal to noise ratio (SNR) improvement factor is derived. Bit error rate (BER) improvement gained by the DSSS communication system using the filter with the optimized notch bandwidth is also shown. Computer simulation results are compared with those obtained analytically to demonstrate the validity of theoretical predictions for various received signal parameters.

This paper suggests that a watermarking technique based on the number theoretic transform (NTT) may effectively be employed for detecting alterations on lossless digital master images. Due to its fragility, the NTT-based technique is sensitive to detecting alterations, compared with that based on the discrete Fourier transform (DFT).

Hypercomplex coefficient digital filters provide several attractive advantages such as compact realization with reduced system order, inherent parallelism. However, they also possess a drawback in that a multiplier requires a large amount of computations. This paper proposes a computationally efficient implementation of digital filters whose coefficient is a type of hypercomplex number; a bicomplex number. By decomposing a bicomplex multiplier into two parallel complex multipliers, we show that hypercomplex digital filters can be implemented as two parallel complex digital filters. The proposed implementation offers more than a 60% reduction in the count of real multipliers.

Reactive near field reflection characteristics of commercial RF absorbers are investigated to determine the minimum size of a reactive-field anechoic box necessary for measuring the reactive near field of an ESPAR antenna. The reflectivity of the absorber placed in close proximity to an antenna is inversely proportional to the distance between the antenna and the absorber. For carbon filled urethane foam tapered absorbers, we find that the backscattered reflection characteristics mainly depend on their tapered height rather than the thickness of absorber base. As a result, we show that carbon filled urethane foam pyramidal and wave surface shaped absorbers can be used to make reactive-field anechoic boxes. A prototype of a reactive-field anechoic box is presented and the distance from the absorber to the antenna is reduced to a wavelength. The prototype is verified by comparing its performance with that obtained from a large anechoic chamber.

We consider bandwidth-efficient modulation schemes for use on non-linear channels, such as that due to a non-linear high power amplifier (HPA) in a wireless system. Continuous Phase Modulation (CPM) schemes are known to perform well on such channels, because they have constant amplitude, but their bandwidth efficiency is low. N-MSK improves this by superposing two or more such signals, but this results in a non-constant amplitude. In this paper we investigate the performance of N-MSK on a non-linear channel, modelled using a travelling wave tube (TWT) non-linearity. We first consider the spectrum and the BER performance of N-MSK on a non-linear channel, making use of the Euclidean distance spectrum of the modulated signal. We then consider the effect of non-linear amplification on these properties. Signal spectrum was determined by simulation, since no closed-form expression is available when the effect of AM-PM conversion are included. We find that the spectrum is remarkably little affected, being only slightly broadened. BER is also evaluated by direct simulation, as well as from the Euclidean distance spectrum. The latter now exhibits a series of clusters, instead of discrete lines, and we find that at least the whole of the first cluster must be considered in calculating the BER, not just the minimum distance or the centroid of the cluster. The detector used in the simulation applies an inverse distortion function, then uses maximum-likelihood sequence estimation (MLSE) set up for the linear channel. This is no longer optimum, because the noise is distorted, and therefore it is also compared with a true MLSE detector. We find that the BER performance is, however, somewhat degraded compared to the linear channel. We determine back-off levels from saturation to optimise overall power efficiency.

In this paper a low-complexity and high-resolution algorithm to estimate the magnitude of complex numbers is presented. Starting from a review of previous art, the new algorithm has been derived to improve precision performance without any penalty in hardware complexity. As a case example, a semi-custom VLSI implementation for 10 bit 2's complement input data has been performed. A mean square error and mean error performance improvement of nearly one order of magnitude has been demonstrated for an hardware complexity increase of roughly 34% with respect to previously presented solutions.

In this paper, we propose a new coded orthogonal frequency division multiplex (COFDM)-based ubiquitous antenna system, which is composed of multiple radio base stations (RBSs) deployed over the service area and Radio-on-Fiber (RoF) link that connects RBSs to the central control station (CCS). The proposed system is capable of receiving multiple mobile terminals simultaneously operating at the same frequency by making effective use of joint detection. However, the propagation delay due to the RoF link could be a major problem for realizing the ubiquitous antenna system. In order to overcome this delay problem, we assume that the guard interval of COFDM is longer than the delay difference. Furthermore, in order to improve BER performance in a multipath Rayleigh fading channel, we also propose the MSE normalization scheme followed by the use of an MMSE-based joint detector. Computer simulation results show that the proposed system can improve the frequency utilization efficiency of the broadband wireless access system.

In this paper, we study the following problem: given two graphs G, H and an isomorphism φ between an induced subgraph of G and an induced subgraph of H, compute the number of isomorphisms between G and H that do not contradict φ. We show that this problem can be solved in O(((k+1)(k+1)!)2n3) time when the input graphs are restricted to chordal graphs with clique number at most k+1. To prove this, we first show that the tree model of a chordal graph can be uniquely constructed in O(n3) time except for the ordering of children of each node. Then, we show that the number of φ-isomorphisms between G and H can be efficiently computed by use of the tree model.

Many researches have been conducted on the recognition of Thai characters. Different approaches, such as neural network, syntactic, and structural methods, have been proposed. However, the success in recognizing Thai characters is still limited, compared to English characters. This paper proposes an approach to recognize the printed Thai characters using the hybrid of global feature, local features, fuzzy membership function and the neural network. The global feature classifies all characters into seven main groups. Then the local features and the neural network are applied to identify the characters.

A uni-traveling-carrier refracting-facet photodiode, a short-stab bias circuit, and a patch antenna are monolithically integrated to make a compact and low-cost photonic millimeter-wave emitter for fiber-radio applications. The device emits the maximum effective radiation power of 173 dBm at 60 GHz including a directive gain of the patch antenna.

We propose a subchannel power control scheme in the OFDM system, which transmits data with a variable power level for each subchannel based on the received SNR. The OFDM system, employing the D-QPSK modulation and the proposed subchannel power control with a grouping coefficient equal to 3, gives about 2.3 dB gain in Eb/N0 comparing with the conventional OFDM system, under the two-ray multipath channel with the mean value of the second-ray's attenuation coefficient equal to 0.25, for the required BER equal to 10-5.