Voice over wireless local area network

This paper introduces the special issue on voice over wireless local area networks (VoWLAN), which aim to foster interaction among researchers from both academia and industry in networking, wireless communications, and mobile computing. The special issue includes an article investigating the issue of determining an appropriate pricing strategy for VoWLAN provisioning. Also featured are two articles on polling as a solution for supporting real-time traffic over WLANs and another on media optimization network architecture (MONA).     

A Novel Test Point Selection Method for Analog Fault Dictionary Techniques

Most of the recently reported test point selection algorithms for analog fault dictionary techniques are based on integer-coded table (ICT) technique. Hence, the accuracy of these algorithms is closely related to the accuracy of the ICT technique. Unfortunately, this technique is not accurate, especially when the size of fault dictionary is large. This paper proposes an accurate fault-pair Boolean table technique for the test point selection problem. First, the approach to transform the fault dictionary into a fault-pair Boolean table is introduced. Then, a test point selection algorithm based on the fault-pair Boolean table is proposed. Thirdly, several example circuits are used to illustrate the proposed algorithm. Simulated results indicate that the proposed method is more accurate than the other methods. Therefore, it is a good solution for minimizing the size of the test point set.     

A Queuing Theory-Enabled Dynamic Bandwidth Allocation Algorithm for a Wired-Wireless Converged Network

Multi-sink wireless sensor networks (WSNs) are being increasingly deployed in an ever-widening range of application scenarios, especially as they are reliable and exhibit low power consumption. Providing a backhaul for WSN traffic has become an important issue because the sensor data must usually be sent to the Internet or the core network. Passive optical networks (PONs) represent one next-generation access network technology which is appropriate for such a backhaul, however existing research appears to have concentrated on either WSN performance or PON performance, without considering the overall performance of both networks converged together. This paper proposes a new architecture which converges multi-sink WSNs and PONs, then provides a novel queuing-theory analysis of the converged network performance. Results from this analytical model are then used to motivate a new a DBA algorithm which optimizes grant size allocation. Numerical results show that this algorithm outperforms existing proposals when minimizing the system queue length in the converged network, while providing shorter end-to-end packet delay and higher throughput. We believe that this first resource allocation algorithm which considers the performance of both networks as one converged unit.     

A Hybrid Domain Block Equalizer for Single-Carrier Modulated Systems

Poor performance in the presence of multipath with long delay spread has been considered as one of the main weaknesses of most single carrier modulated systems, including ATSC (advanced television systems committee) system. The introduction of distributed transmission network and single frequency network brings new challenges for the ATSC equalizer design, since the delay spread of a multipath channel under such scenarios becomes significantly longer than the traditional broadcasting practice of using one high power transmitter to cover a wide area, where the multipath distortion is mainly from reflected echoes. An iterative hybrid frequency-time domain equalizer for ATSC system is proposed in this paper based on our block-based interference analysis. The multipath distortion in the received ATSC signal is first tentatively removed with a frequency domain equalizer on a block-by-block basis. However, inter-block and intra-block interferences still exist due to the lack of cyclic structure in the received ATSC signal. A time domain interference cancellation algorithm is then used to cancel the inter-block interference and intra-carrier interference, based on the tentative decisions in time domain after the frequency domain equalization. These two steps are iterated until desired receiver performance is achieved. The proposed equalizer and the subsequent analysis are verified through numerical simulations.     

Application of Rollout Strategy to Test Points Selection for Integer-Coded Fault Wise Table

Test points selection for integer-coded fault wise table is a discrete optimization problem. The global minimum set of test points can only be guaranteed by an exhaustive search which is eompurationally expensive. In this paper, this problem is formulated as a heuristic depth-first graph search problem at first. The graph node expanding method and rules are given. Then, rollout strategies are applied, which can be combined with the heuristic graph search algorithms, in a computationally more efficient manner than the optimal strategies, to obtain solutions superior to those using the greedy heuristic algorithms. The proposed rollout-based test points selection algorithm is illustrated and tested using an analog circuit and a set of simulated integer-coded fault wise tables. Computa- tional results are shown, which suggest that the rollout strategy policies are significantly better than other strategies.     

液晶TFT有源矩阵单元性能分析

本文详细分析液晶薄膜晶体管(TFT)有源矩阵单元性能.其中包括薄膜晶体管单元结构特性和液晶单元电容充放电物理过程。通过分析,推导出有用的计算公式。这些结果对实际工作具有指导作用。     

Medium access control in ultra-wideband wireless networks

Ultra-wideband (UWB) transmission is an emerging wireless communication technology with unique potential merits such as high-rate, low-transmission power, immunity to multipath propagation, and capability in precise positioning. It has received significant interests for future wireless communications from both academia and industry. In UWB wireless networks, medium access control (MAC) is essential to coordinate the channel access among competing devices. The unique UWB characteristics not only pose significant challenges but also offer great opportunities in efficient UWB MAC design. This paper presents a comprehensive overview of UWB MAC development on four important aspects: multiple access, overhead reduction, resource allocation, and quality of service (QoS) provisioning, and identifies some future research issues.     

酸性pH滑移剂对锦纶织物染色性能的研究

对自制酸性pH滑移剂EY与日产酸性pH滑移剂PC的滑移性能进行了对比 ,试验表明 ,只要在酸性pH滑移剂EY中加入微量催酸剂K ,其滑移性能与日产酸性pH滑移剂PC接近。同时 ,两者对锦纶织物的染色性能与传统醋酸染色工艺相比 ,它们的竭染率相似 ,但匀染性明显好于醋酸染色工艺。     

3σ-rule-based early termination algorithm for mode decision in H.264

A low-complexity early termination algorithm for mode decision in H.264 is presented. The proposed algorithm is based on the statistical distribution of per-pixel motion cost, and it can skip the mode decision of the candidate macroblock modes with low probability. Simulation results reveal that the proposed algorithm can reduce the encoding time by 16.25% on average with the limited performance loss of about 0.023% dB.     

模块化无线mesh网络加密方案设计

文章在基于装有OpenWrt和Click的无线路由器所搭建的无线mesh网络测试床上,研究使用Click模块化路由编程工具,结合802.11i和802.11s草案针对无线mesh网络安全的协议设计方案,提出在无认证服务器环境中,使用预共享密钥进行数据包链路层加密以确保mesh节点间通信保密可靠的安全解决方案.