Design and performance of BICM-ID systems with hypercube constellations

This paper introduces new mappings of QPSK symbols, viewed as a multi-dimensional hypercube, to improve the performance of bit-interleaved coded modulation with iterative decoding (BICM-ID). By evaluating the upper bound of the bit error rate performance of BICM-ID, a condition to find the best mapping of a hypercube constellation in terms of the asymptotic performance under different channel models is established. A general and simple algorithm to construct the best mapping of a hypercube is then proposed. Analytical and simulation results show that the use of the proposed mappings together with very simple convolutional codes can offer significant coding gains over the conventional BICM-ID systems for all the channel models considered. Such coding gains are achieved without bandwidth or power expansion and with a very small increase in the system complexity.     

多维映射BICM-ID系统的简化MD-LSD解映射算法

将二维映射下的软输入软输出解映射MAX-LOG-MAP算法扩展到多维映射比特交织编码调制及迭代译码(BICM-ID)系统,并首次结合多天线系统下的列表球形译码,提出一种简化MD-LSD(multi-dimensional list sphere decoding)算法.新算法大幅降低了多维解映射的计算复杂度.仿真结果表明,列表长度满足一定范围时,采用简化MD-LSD算法解映射算法的性能损失可以忽略.     

Improving the climbing/descent performance of stair-climbing mobility systems confronting architectural barriers with geometric disturbances

This paper presents a new study on the obstacle-climbing ability of Stair-Climbing Mobility Systems (SCMSs), taking into account the effects related to the presence of geometric disturbances on the obstacles. In this research, we use an SCMS that combines two different locomotion mechanisms to climb up and down stairs: one based on wheels and the other based on Sliding Supports. The combination of these mechanisms allows stairs of different sizes, and even stairs with geometric disturbances such as stairs with irregular or uneven treads, to be surpassed. However, the difficulty of the obstacle-climbing problem increases if the stair height is either large or its geometry is altered, in which case the obstacle climbing ability, and consequently the user’s safety may be highly compromised. In order to increase its adaptability to large-sized stairs and to reduce the effect of geometric disturbances, two important improvements have been made to the previous SCMS. One of these has been achieved by incorporating appropriate drive systems and redesigning the mechanisms that control the wheels. Thanks to this, the proposed SCMS is more lightweight and easy to control, and is above all more robust to geometric disturbances on the obstacles. The other concerns the trajectory planning, which has been improved by using a strategy that allows the size and shape of the stair to be estimated and accordingly allows a smooth and accurate reference trajectory to be tracked. This strategy is based on information obtained from laser distance sensors. This second improvement simplifies the control problem, reduces the time needed to surpass stairs and improves the user’s safety and comfort. Experimental results demonstrate the effectiveness of the proposed improvements when the SCMS climbs/descends staircases when both considering and not considering the effects of geometric disturbances on the steps.     

Improving the performance of fuzzy classifier systems for patternclassification problems with continuous attributes

In this paper, various methods are introduced for improving the ability of fuzzy classifier systems to automatically generate fuzzy if-then rules for pattern classification problems with continuous attributes. First, we describe a simple fuzzy classifier system where a randomly generated initial population of fuzzy if-then rules is evolved by typical genetic operations, such as selection, crossover, and mutation. By computer simulations on a real-world pattern classification problem with many continuous attributes, we show that the search ability of such a simple fuzzy classifier system is not high. Next, we examine the search ability of a hybrid algorithm where a learning procedure of fuzzy if-then rules is combined with the fuzzy classifier system. Then, we introduce two heuristic procedures for improving the performance of the fuzzy classifier system. One is a heuristic rule generation procedure for an initial population where initial fuzzy if-then rules are directly generated from training patterns. The other is a heuristic population update procedure where new fuzzy if-then rules are generated from misclassified and rejected training patterns, as well as from existing fuzzy if-then rules by genetic operations. By computer simulations, we demonstrate that these two heuristic procedures drastically improve the search ability of the fuzzy classifier system. We also examine a variant of the fuzzy classifier system where the population size (i.e., the number of fuzzy if-then rules) varies depending on the classification performance of fuzzy if-then rules in the current population     

Improving performance of multi-user OFDM systems using bit-wiseinterleaver

A new bit-wise interleaver is introduced for multi-user orthogonal frequency division multiplexing systems using frequency hopping. In addition to placing adjacent bits (belonging to one complex I/Q symbol) onto different subcarriers, they can be placed at different timeslots or different blocks. Furthermore, the interleaver can be adjusted adaptively based on the corresponding hopping pattern. The performance gain is investigated by simulations     

Network covert timing channel with distribution matching

Network covert timing channel is a communication fashion that modifies the timing properties of network traffic to transfer secret information. It is designed to carry out the reliable and undetectable transmission. In this paper, a simple and secure covert timing channel method with distribution matching is proposed. The approach treats the network traffic as the flow with the fixed-length fragment, and calculates the histogram of the packet delays in each fragment. The message bits are modulated into the delays by the binary coding method, and the histogram is kept almost unchanged by assigning the matched distribution. The bit error rates are analyzed and two detection experiments are performed. The results show the proposed method is reliable and undetectable.     

New layout strategies with improved matching performance

In this paper, the systematic mismatch error in integrated circuits due to gradient effects is modeled and analyzed. Three layout strategies with improved matching performance are reviewed and summarized. The hexagonal tessellation pattern can cancel quadratic gradient errors with only 3 units for each device and has high area-efficiency when extended. Both the Nth-order circular symmetry patterns and Nth-order central symmetry patterns can cancel up to Nth-order gradient effects between two devices using 2^N unit cells for each one. Among these three techniques, the central symmetry patterns have the best-reported matching performance for Manhattan structures; the circular-symmetry patterns have the best theoretical matching performance; and the hexagonal tessellation pattern has high density and high structural stability. The Nth-order central symmetry technique is compatible to all IC fabrication processes requiring no special design rules. Simulation results of these proposed techniques show better matching characteristics than other existing layout techniques under nonlinear gradient effects. Specifically, two pairs of P-poly resistors using 2nd and 3rd-order central symmetry patterns were fabricated and tested. Less than 0.04% mismatch and less than 0.002% mismatch were achieved for the 2nd and the 3rd-order structures, respectively. Chengming He was born in YiWu, China in 1976. He received his B.S. in 1999 in Electronic Engineering department and his M.S. degree in the institute of Microelectronics in 2001 at Tsinghua University, Beijing. He started to work toward his PhD in Iowa State University since August 2001. Since June 2004 he started to work as a design engineer in Silicon Laboratories, Inc., Austin, TX. He studied and designed LNA, band-pass filter and on-chip power management blocks as well as matching-enhanced layout patterns. He is interested in designing high gain low voltage amplifier, high speed power-efficient ADC and high speed high linear DAC as well as other mixed-signal circuits. He is also interested in the application of nonlinear system dynamical theory in mixed-signal design and yield-enhancement by improving layout matching. He has published more than 10 technical papers. He was a student member of IEEE from 01--04 and now is a member. He is a member of Tau Beta Pi. Xin Dai was born in Shanghai, China on March 11, 1981. She received the B.Eng. in 2003 from Shanghai Jiao Tong University, Shanghai, China. She is currently a graduate student in Department of Electrical and Computer Engineering at Iowa State University, Ames, IA. Her research has been connected to data converter design and calibrations, layout techniques and build-in-self-test. Xin Dai is now taking a summer-intern in Broadcom Corp., CA. Hanqing Xing was born in Dalian, China, in 1978. He received the B.S. and M.S. degrees with honors in Electronic Engineering from Tsinghua University, Beijing, China, in 2000 and 2003, respectively. He is currently a PhD student at Iowa State University working in analog and mixed signal design group. His research interests include analog, mixed-signal, and data-conversion integrated circuits design and test. Degang Chen received his B.S. degree in 1984 in Instrumentation and Automation from Tsinghua University, Beijing, China and his M.S. and Ph.D. degrees in 1988 and 1992, respectively, both in Electrical and Computer Engineering, from the University of California, Santa Barbara. From 1984 to 1986, he was with the Beijing Institute of Control Engineering, a space industry R/D institute. From March 1992 to August 1992, he was the John R. Pierce Instructor of Electrical Engineering at California Institute of Technology. After that, he joined Iowa State University where he is currently an Associate Professor. He was with the Boeing Company in summer of 1999 and was with Dallas Semiconductor-Maxim in summer of 2001. His research experience include particulate contamination in microelectronic processing systems, vacuum robotics in microelectronics, adaptive and nonlinear control of electromechanical systems, and dynamics and control of atomic force microscopes. His current teaching and research interests are in the area of analog and mixed-signal VLSI integrated circuit design and testing. In particular, he is interested in low-cost high-accuracy testing and built-in-self-test of analog and mixed-signal and RF circuits, and in self-calibration and adaptive reconfiguration/repair strategies for performance and yield enhancement. Dr. Chen is the recipient of the Best Paper Award at the 1990 IEEE Conference on Decision and Control and the Best Transaction Paper Award from the ASME Journal of Dynamic Systems, Measurement, and Control in 1995. He was selected an A.D. Welliver Faculty Fellow with the Boeing Company in 1999.     

DMS impact on the technical and economical performance of the distribution systems

6. Conclusions  The distribution system, one of the major components of an electric power system, has traditionally been characterized as the most unglamorous component. Nowadays, armed with commercially available software (DMS/SCADA) and hardware, the distribution utilities have the possibility to manage the immense amount of the information (data), to optimize the internal resources, to maintain a reliable and cost effective energy supply and to be prepared for the future operation strategies while increasing the company revenue. Kurzfassung eines Fachbeitrags bei der 18. CIRED — Internationale Konferenz über Verteilungsnetze für elektrische Energie, die vom 6. bis 9. Juni 2005 in Turin, Italien, stattfand.     

Improving the photocatalytic performance of TiO2 via hybridizing with graphene

In this paper an improvement in the photocatalytic performance of TiO₂ was carried out via hybridizing with graphene. Graphene-TiO₂ (GR-TiO₂)nanocomposites with different weight addition ratios of graphene oxide (GO) have been prepared via a facile microwave irradiation of GO and tetrabutyl titanate in isopropyl alcohol. Raman spectroscopy (RS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis), Fourier transform infrared spectra (FTIR), energy dispersive X-ray spectroscopy (EDX) and photoluminescence spectra (PL) are employed to determine the properties of the samples. Microwave irradiation can heat the reactant to a higher temperature in a short time, simultaneously GO is reduced to graphene and TiO₂ nanoparticles grown on the surface of GR. GR-TiO₂ nanocomposites synthesized via this approach have efficient electron conductivity in GR, resulting in a reduced electron-hole recombination rate. Among the synthesized nanocomposites, GT-8wt% exhibited the best photocatalytic activity toward photocatalytic degradation of MB. Our current work provides a new insight for the fabrication of GR-TiO₂ nanocomposites within a short reaction time and also explains the mechanism of photocatalysis employing radical and hole scavengers.     

Improving performance of DS-CDMA systems using chaotic complex Bernoulli spreading codes

The most important goal of spreading spectrum communication system is to protect communication signals against interference and exploitation of information by unintended listeners. In fact, low probability of detection and low probability of intercept are two important parameters to increase the performance of the system. In Direct Sequence Code Division Multiple Access (DS-CDMA) systems, these properties are achieved by multiplying the data information in spreading sequences. Chaotic sequences, with their particular properties, have numerous applications in constructing spreading codes. Using one-dimensional Bernoulli chaotic sequence as spreading code is proposed in literature previously. The main feature of this sequence is its negative auto-correlation at lag of 1, which with proper design, leads to increase in efficiency of the communication system based on these codes. On the other hand, employing the complex chaotic sequences as spreading sequence also has been discussed in several papers. In this paper, use of two-dimensional Bernoulli chaotic sequences is proposed as spreading codes. The performance of a multi-user synchronous and asynchronous DS-CDMA system will be evaluated by applying these sequences under Additive White Gaussian Noise (AWGN) and fading channel. Simulation results indicate improvement of the performance in comparison with conventional spreading codes like Gold codes as well as similar complex chaotic spreading sequences. Similar to one-dimensional Bernoulli chaotic sequences, the proposed sequences also have negative auto-correlation. Besides, construction of complex sequences with lower average cross-correlation is possible with the proposed method.     

Improving the performance of active buffer management with per-flowinformation

This letter proposes a new technique to improve the performance of active queue management (AQM) with per-flow information such as balanced random early detection (BRED). The technique is virtual buffer occupancy, which represents not the actual buffer occupancy but the buffer occupancy as it would be if packets were serviced in a fair round robin fashion. In AQM using virtual buffer occupancy, packets of flow i are dropped based on the virtual buffer occupancy of flow i. We show that BRED using virtual buffer occupancy achieves fairer bandwidth allocation than original BRED     

EXIT chart analysis of BICM-ID with imperfect channel state information

We analyze the convergence of iteratively decoded bit-interleaved coded modulation with imperfect channel state information using the extrinsic information transfer (EXIT) chart. A canonical analysis model is adopted, where the power correlation coefficient between the fading and its estimate becomes the key parameter affecting the extrinsic transfer characteristics of the demapper and hence the convergence of iterative decoding. We further illustrate that decoding convergence can be triggered by tradeoff between the quality of channel estimation and code rate.     

Improving the performance of switched diversity with post-examining selection

Switched diversity offers one of the lowest complexity solution for fading mitigation. The receiver employing switched combining schemes. seeks and uses an acceptable diversity path for data reception. However, when no acceptable path is found after all paths have been examined, the receiver ends up randomly choosing an unacceptable path. In this paper, we consider the performance improvement of switched combining schemes. In particular, we modify conventional multi-branch switch and examine combining (SEC) schemes in a way that the best path is selected when no acceptable path is found after all paths have been examined. We carry out a thorough performance versus complexity tradeoff study on the resulting scheme: SEC with post-examining selection and illustrate the study with some selected numerical examples.     

Wide-band impedance matching: H/sup /spl infin// performance bounds

This paper presents the first implementation of Helton's H/sup /spl infin// approach to wide-band impedance matching. The prototypical problem is to maximize the transducer power gain uniformly over an operating band for a load connected to a generator by a lossless two-port. The H/sup /spl infin// approach computes the maximum transducer power gain attainable by any lossless two-port uniformly over the operating band. This maximum gain is computed for Fano's classic RLC circuit and an high-frequency antenna represented by measured reflectance data.     

Improving UDP performance using intermediate QoD‐aware hop system for wired/wireless multimedia communication systems

Multimedia communication in wireless networks is challenging due to the inherent complexity and constraints of multimedia data. To reduce the high bandwidth requirement of video streaming, videos are compressed by exploiting spatial and temporal redundancy, thus yielding dependencies among frames as well as within a frame. Unnecessary transmission and maintenance of useless packets in the buffers cause further loss and degrade the quality of delivery (QoD) significantly. In this paper, we propose a QoD‐aware hop system that can decide when and which packets could be dropped without degrading QoD. Moreover, the transmission of useless packets causes network congestion and vain payment by the wireless system subscriber. In this paper, we focus on two types of frame discarding policies to maintain QoD: partial frame discarding policy (PFD) and early frame discarding policy (EFD). PFD policy discards the succeeding packets of a frame if a packet of the frame cannot be served. On the other hand, in EFD policy, when it is likely to fail to serve packets of a frame (based on a threshold) the subsequent packets of the frame are discarded. We first provide an analytical study of average buffer occupancy based on these discarding policies and show the closed‐form expressions for average buffer occupancy. We then perform our simulations by implementing a Markovian model and measure the frameput (the ratio of number of frames served) rather than the number of packets served. Copyright © 2011 John Wiley & Sons, Ltd.     

Improving handoff performance by utilizing ad hoc links in multi-hop cellular systems

Handoff performance is a critical issue for mobile users in wireless cellular networks, such as GSM networks, 3G networks, and next generation networks (NGNs). When ad hoc mode is introduced to cellular networks, multi-hop handoffs become inevitable, which brings in new challenging issues to network designers, such as how to reduce the call dropping rate, how to simplify the multi-hop handoff processes, and how to take more advantage of ad hoc mode for better resource management, and most of these issues have not been well addressed as yet. In this paper, we will address some of the issues and propose a scheme, Ad-hoc-Network–Embedded handoff Assisting Scheme (ANHOA), which utilizes the self-organizing feature of ad hoc networks to facilitate handoffs in cellular networks and provide an auxiliary way for mobile users to handoff across different cells. Moreover, we also propose a scheme enabling each BS to find the feasible minimum reservation for handoff calls based on the knowledge of adjacent cells’ traffic information. Due to the use of multi-hop connections, our scheme can apparently alleviate the reservation requirement and lower the call blocking rate while retaining higher spectrum efficiency. We further provide a framework for information exchange among adjacent cells, which can dynamically balance the load among cells. Through this study, we demonstrate how we can utilize ad hoc mode in cellular systems to significantly improve the handoff performance.     

Improving the performance of microstrip-patch antennas

This paper describes a cavity-backed patch-antenna geometry, which features multiple dielectric layers and shorting posts. These features are exploited to design antennas which retain many of the desirable characteristics of conventional microstrip antennas, yet overcome some of their inherent disadvantages     

Improving CSMA/CA network performance under hidden collision

Dynamic spectrum access policy allows a secondary user (SU) to access a primary user (PU) channel when it is idle. However, the idle state may result from the PU's silent activities, which can be wrongly perceived as an opportunity for the SU to access the channel and lead to “hidden collision” when it effectively tries to access the channel under this condition. At best of our knowledge, this issue has yet to be addressed in the literature. In this paper, we will first define a three‐state model that describes hidden collision conditions, then propose a probabilistic model in which a transient state is added to force the SU to wait a certain period of time before accessing the channel, thereby translating into better protection for the PU. Based on this model and using Carrier Sense Multiple Access/Collision Avoidance protocol, we will evaluate the PU's and SU's throughput and delay with and without transient state as well as the gain in using our approach. Our computation results show a substantial improvement of the PU's throughput from 19.6 to 61.1%.     

The use of WMC distribution for performance evaluation of APDoptical communication systems

In the analysis of the bit-error rate (BER) of an optical communication system with avalanche photodiode (APD) detectors, the Webb, McIntyre, Conradi (1974) distribution has been often used to approximate the APD receiver output statistics. This paper presents new simple and closed form BER expressions as well as an importance sampling technique for optical systems employing APD receivers when the WMC model is used. Comparison of the WMC model with the exact model is also carried out. In particular, it is shown that the WMC distribution is quite accurate and has the advantage of simplicity for both simulation and analysis