The present paper discusses a new construction of UWB pulses within the framework of soft-spectrum adaptation. The employed basis functions are B-splines having the following properties: (i) The B-splines are time-limited piecewise polynomials. (ii) The first-order B-splines are rectangular pulses and they converge band-limited functions at the limit that their order tends to infinity. (iii) There are an analog circuit and a fast digital filter for the generation of B-splines. Simple application of Gram-Schmidt orthonormalization process to the shifted B-splines results in a few basic pulses, which are well time-limited and have a broad band width, but do not comply with the FCC spectral mask. A constrained approximation technique is proposed for adaptively designing pulses so that they approximate target frequency characteristics. At the cost of using eleven shifted B-splines, an example set of four pulses comforting the FCC spectral mask is obtained.

To increase the number of the embedded secrets and to improve the quality of the stego-image in the vector quantization (VQ)-based information hiding scheme, in this paper, we present a novel information-hiding scheme to embed secrets into the side match vector quantization (SMVQ) compressed code. First, a host image is partitioned into non-overlapping blocks. For these seed blocks of the image, VQ is adopted without hiding secrets. Then, for each of the residual blocks, SMVQ or VQ is employed according to the smoothness of the block such that the proper codeword is chosen from the state codebook or the original codebook to compress it. Finally, these compressed codes represent not only the host image but also the secret data. Experimental results show that the performance of the proposed scheme is better than other VQ-based information hiding scheme in terms of the embedding capacity and the image quality. Moreover, in the proposed scheme, the compression rate is better than the compared scheme.

Many routing protocols have been proposed for mobile ad hoc networks. Among these protocols, the on-demand routing protocols are very attractive because they have low routing overhead. However, few of the existing on-demand routing protocols have considered the link heterogeneity, such as the different communication rate, different Packet Error Ratio (PER). As a result, the routes tend to have the shortest hop count and contain weak links, which usually provide low performance and are susceptible to breaks in the presence of mobility. In this paper, we analyze the existing on-demand routing protocols and propose a Link Heterogeneity Aware On-demand Routing (LHAOR) protocol, where the link quality and mobility are considered. Specifically, the Local Update (LU) is proposed and the link metric is inversely related with the Received Signal Strength Indicator (RSSI). By using the LU method and RSSI information, the routes adapt to the topology variation and link quality changes, and reach the local optimum quickly, which contains strong links and has a small metric. Simulation and experiment results show that our LHAOR protocol achieves much higher performance than the classical on-demand routing protocols.

Over the past few years, a considerable number of studies have been conducted on modeling the bargaining game using artificial agents on within-model interaction. However, very few attempts have been made at study on the interaction and co-evolutionary process among heterogeneous artificial agents. Therefore, we present two kinds of artificial agents, based on genetic algorithm (GA) and reinforcement learning (RL), which play a game on between-model interaction. We investigate their co-evolutionary processes and analyze their parameters using the analysis of variance.

Diagonally weighted space-time trellis codes using one-bit feedback of channel information are considered. We derive performance criteria for designing STTC and weighting matrix in perfect feedback channel. A simple modification of conventional STTC using unitary rotation is proposed and some modified STTCs are found through computer search. Simulation results show that the modified STTCs achieve the improved performance over a wide range of feedback channel condition.

This paper introduces the concept of measuring double directional channels in ultra wideband (UWB) systems. Antenna-independent channel data were derived by doing the measurements in a wooden Japanese house. The data were useful for investigating the impact of UWB antennas and analyzing waveform distortion. Up to 100 ray paths were extracted using the SAGE algorithm and they were regarded as being dominant. The paths were then identified in a real environment, in which clusterization analyses were done using the directional information on both sides of the radio link. Propagating power was found to be concentrated around the specular directions of reflection and diffraction. This led to the observation that the spatio-temporal characteristics of extracted paths greatly reflected the structure and size of the environment. The power in the clusters indicated that the estimated 100 paths contained 73% of the total received power, while the rest existed as diffuse scattering, i.e., the accumulation of weaker paths. The practical limits of path extraction with SAGE were also discussed. Finally, we derived the scattering loss and intra-cluster properties for each reflection order, which were crucial for channel reconstrucion based on the deterministic approach.

We study the complexity of the reachability problem for a new subclass of Petri nets called simple-circuit Petri nets, which properly contains several well known subclasses such as conflict-free, BPP, normal Petri nets and more. A new decomposition approach is applied to developing an integer linear programming formulation for characterizing the reachability sets of such Petri nets. Consequently, the reachability problem is shown to be NP-complete. The model checking problem for some temporal logics is also investigated for simple-circuit Petri nets.

This paper presents a new transmission scheme of M-ary biorthogonal pulse position modulation (BPPM) in ultra wideband systems. The proposed scheme incorporates position-wise parity information to improve the probability of symbol detection over multipath channels. A linear filter-based channel modification is also introduced to mitigate multipath degradation and maximize the probability of symbol detection by using parity information. The analytical and numerical results show that the proposed scheme achieves a significant improvement of symbol error rate (SER) with very low computational complexity and no symbol delay.

For a CDMA system with a single carrier, we consider a call control policy at each cell, which gives priority to handoff calls over new calls while meeting the overall call quality. New calls are first under the call control of the threshold type, and then receive services together with the handoff calls but under the outage restriction guaranteeing a pre-specified call quality. An optimization model with such quality-guaranteeing constraints is formulated, which is to determine the threshold value for each cell, minimizing the new call blocking probability. We propose a solution heuristic, with which a number of simulations are conducted under a variety of traffic environments. The computational experiments evaluate the usefulness of our call control scheme in that handoff calls are given an appropriate level of priority while the system capacity is effectively utilized.

In this paper, we propose an agent architecture for a combination of speculative computation and abduction. Speculative computation is a tentative computation when complete information for performing computation is not obtained. We use a default value to complement such incomplete information. Unlike usual default reasoning, the real value for the information can be obtained during the computation and the computation can be revised on the fly. In the previous work, we applied this technique to handling distributed problem solving under incomplete communication environments in the context of multi-agent systems and proposed correct procedures in abductive logic programming in terms of perfect model semantics. In the previous work, however, we regarded assumptions as defaults and used these assumptions for speculative computation. Thus, we could not perform hypothetical reasoning, that is, the original usage of abduction. In this paper, we extend our framework so that speculative computation and abduction can be both performed. As a result, our procedure becomes an extension of the abductive procedure developed by Kakas and Mancarella augmented by dynamic belief revision mechanism about outside world.

The effect of a cavity on the third-order optical nonlinearity, is studied for a two-level system with excitation frequency ω0, as a function of the Q factor, coupling constant g, and longitudinal (γ1) and pure transverse (γ2) damping constants. The largest enhancement is found in the strong-coupling regime with γ1+2γ2=ω0/2Q. Large enhancement is also achieved in the weak-coupling regime satisfying the condition , and the intensity depends on damping constants only. The calculation is based on the cavity QED because the semiclassical treatment of the cavity quasimode leads to incorrect optical nonlinearity.

Dly-ACK scheme in IEEE 802.15.3 MAC is designed to reduce the overhead of the ACK frame in MAC layer and improve the channel utilization. However, how to using the Dly-ACK is open for implementation. In this paper, we propose an adaptive Dly-ACK scheme for both TCP and UDP traffic. We first point out the problems of applying fixed Dly-ACK scheme to these two traffic scenarios and show that the system performance is rather poor and the causes of these problems are presented. Based on our observations, two enhancement mechanisms for fixed Dly-ACK are then proposed. The first one is to request the Dly-ACK frame adaptively or change the burst size of Dly-ACK according to the transmitter queue status. The second is a retransmission counter to enable the destination DEV to deliver the MAC data frames to upper layer timely and orderly. Simulation results show that, with our enhancements, the system performance can be improved significantly compared with the conventional Imm-ACK and fixed Dly-ACK. We also investigate the impacts of some important parameters such as the buffer size on the system performance. Some important guidelines for the Dly-ACK design are given. Finally, it is worth to point out that our Dly-ACK enhancements are compatible with the standard and it is transparent to the upper layer protocols, i.e., either UDP or TCP.

A TMTR code is specified as (=2,=3,k) constraint. In this work, an approach for constructing (=2,=3,k) codes is presented. Based on this construction, a rate 8/9 code with k=7 is found. This code can achieve better timing recovery performance compared to the proposed previously TMTR code with k=11. An enumerating encoder and decoder exist for constructed (=2,=3,k) codes. A look-up table for the encoder/decoder is not required. Simulation results on an E2PRIV recording channel reveal that the TMTR code provides 2.2 dB gain over an uncoded case.

A new simple recovery scheme for transient bit errors in the RAM of a ROM-based embedded system is presented, which exploits the information stored in the ROM. And a new scrubbing technique suitable to the proposed recovery scheme is also presented. With the proposed recovery scheme and scrubbing technique, the reliability of the RAM against transient bit errors can be improved remarkably with no additional extra memory and scrubbing overhead.

The explicit construction of a universal source code for correlated sources is presented. The construction is based on a technique of simulated random coding algorithms [5]. The proposed algorithm simulates the random generation of linear codes. For every pair of correlated sources whose achievable rate region includes a given pair of encoding rates, the decoding error rate of the proposed algorithm goes to zero almost surely as the block length goes to infinity.

This paper presents a low-complexity equalization for M-ary biorthogonal keying based direct sequence ultra wideband (MBOK DS-UWB) systems. We focus on a Viterbi equalizer, which is based on maximum likelihood sequence estimation (MLSE). To reduce the computational complexity of MLSE-based equalizer, we use two strategies. One is the use of delayed-decision feedback sequence estimation (DDFSE), which is a hybrid estimation between MLSE and decision feedback estimation (DFE). And the other is the truncation of state transition in MLSE by considering MBOK pulse mapping. The reduced complexity sequence estimation is named as reduced state (RS)-DDFSE. By the use of RS-DDFSE, the complexity of Viterbi equalizer for MBOK DS-UWB is significantly reduced, by comparison with that of MLSE. The performance of RS-DDFSE based equalizer is evaluated on multipath fading channel models provided by IEEE802.15.3a. An analysis on trellis diagram of RS-DDFSE and simulation results show that the impact on error rate performance generated by the complexity lower is slight.

The frequency estimate for a real sinusoid provided by the periodogram has a bias which is particularly severe for a short observation interval. In this paper, two improvements to the periodogram are proposed to reduce this bias. The first method transforms the real tone to a complex sinusoid while the second algorithm subtracts the negative spectral line from the received signal, prior to applying the periodogram. The performance of the two methods is illustrated by comparing with the periodogram and Quinn's interpolation as well as Cramér-Rao lower bound.

This letter proposes two very-low-complexity maximum-likelihood (ML) detection algorithms based on QR decomposition for the quasi-orthogonal space-time code (QSTBC) with four transmit antennas [3]-[5], called VLCMLDec1 and VLCMLDec2 decoders. The first decoder, VLCMLDec1, can be used to detect transmitted symbols being extracted from finite-size constellations such as phase-shift keying (PSK) or quadrature amplitude modulation (QAM). The second decoder, VLCMLDec2, is an enhanced version of the VLCMLDec1, developed mainly for QAM constellations. Simulation results show that both of the proposed decoders enable the QSTBC to achieve ML performance with significant reduction in computational load.

Unwanted electromagnetic emission occurs due to the common-mode current on the cables entering a PC's metal enclosure and can be treated as wire antennas passing through the apertures of the enclosure. To reduce the emission, a stack of metal rings is suggested to be placed around the cable and external to the aperture, adopting the concept of a Coaxial Band-Stop Filter, for the first time. The influence of this novel structure on the common-mode current is examined in the FDTD-method frame work.

A side-coupled microstrip open-loop resonator is presented for design of harmonic-suppressed bandpass filters with compact size. In geometry, the open-ended microstrip feed line is put in close proximity to the loop resonator at the opposite side of an opened-gap. In design, its length is properly lengthened to establish the orthogonal even- and odd-symmetrical current distributions along the two coupled strip conductors. It thus results in cancellation the 1st parasitic resonance. The two-stage open-loop filter is first constructed and its performance is studied under varied feed line lengths. Furthermore, a four-stage filter block is optimally designed at 2.52 GHz and its circuit sample is fabricated with the overall length less than 60% of one guided wavelength. The measured insertion loss at the 1st harmonic is higher than 30 dB, the stopband covers the range from 2.8 GHz to 7.0 GHz, and the dominant pass bandwidth is about 9.0%.