Dynamic Routing with Security Considerations

Security has become one of the major issues for data communication over wired and wireless networks. Different from the past work on the designs of cryptography algorithms and system infrastructures, we aim at the proposing of a dynamic routing algorithm that could randomize delivery paths for data transmission. The algorithm is easy to implement and compatible with popular routing protocols, such as Routing Information Protocol in wired networks and Destination-Sequenced Distance Vector protocol in wireless networks, without introducing extra control messages. An analytic study on the proposed algorithm is presented, and a series of simulation experiments are conducted to verify the analytic results and to show the capability of the proposed algorithm.     

Dynamic Compressive Property of Closed-Cell Mg Alloy Composite Foams Reinforced with SiC Particles

The high-strain-rate mechanical response of Mg alloy/SiC_p composite foams has received increased attention in recent years due to their light weight and potential to absorb large amounts of energy during deformation. Dynamic compressive properties of closed-cell Mg alloy/SiC_p composite foams with diff erent relative densities(0.162, 0.227 and 0.351) and diff erent SiC_p additions(0, 4 and 8 wt%) have been investigated using Split-Hopkinson pressure bar. It is shown that peak stress and energy absorption capacity signifi cantly increase as the relative density increases at the range of testing strain rates. Peak stress and energy absorption display strain rate dependence. The peak stress of specimens with 0 wt% and 4 wt% SiC particles additions grows with increasing strain rate. Meanwhile, the increment in the peak stress of specimens with 8 wt% addition is not signifi cant with strain rate increasing. The increase in strain rate increases the energy absorption capacity. The suitable amount of SiC particles addition has great advantages over increasing the peak stress and energy absorption capacity at the high strain rate. The strain-rate-sensitive matrix, cell morphology, morphological defects and gas pressure have an impact on the strain-rate sensitivity of Mg alloy/SiC_p composite foams.     

Implicit Deregistration with Forced Registration for PCS Mobility Management

Registration/deregistration with a mobility database called Visitor Location Registers (VLRs) is required in a PCS network when a mobile phone moves between registration areas. Several schemes were proposed to deregister a mobile phone after it moves out of a registration area. A simple scheme, called implicit deregistration, is studied in this paper, which does not specifically deregister any obsolete record in the VLR. If the VLR is full when a mobile phone arrives, a record in the VLR is deleted and the reclaimed storage is reassigned to the incoming mobile phone. It is possible that a valid record will be deleted. If so, the VLR record of a mobile phone may be deleted before a call to the mobile phone arrives. Our previous work assumed that the incoming call setup would be lost. In this paper, we propose forced registration to restore the VLR record before the call setup operation can proceed. With this modification, implicit deregistration totally eliminates the deregistration traffic at the cost of creating some forced registration traffic.We derive the record-missing probability and the portion of the network traffic saved by implicit deregistration. Our study indicates that implicit deregistration with forced registration may significantly reduce the deregistration traffic if the user mobility is high and the number of mobile phones in a registration area is not very large.     

Modeling mis-routing calls due to user mobility in wireless VoIP

This letter proposes an analytic model to study the mis-routing problem caused by user mobility in a wireless VoIP system. We derive the probability that there are n mis-routed calls when a subscriber moves from IP network to the GSM network. Our study indicates that if the user residence times in GSM location areas, inter-call origination times and the inter-call delivery times are of the same order, then the mis-routing effect can not be ignored     

Comparing soft and hard handoffs

This paper studies the soft-handoff mechanism and compares its performance with hard handoff. Our study indicates that although a handset may potentially consume extra radio links in soft handoff, the mechanism provides better opportunity to transfer the link successfully in the handoff procedure. Thus, by carefully planning the overlay areas of cells, soft handoff can outperform hard handoff     

An Adaptive GTS Allocation Scheme for IEEE 802.15.4

IEEE 802.15.4 is a new standard uniquely designed for low-rate wireless personal area networks. It targets ultralow complexity, cost, and power for low-rate wireless connectivity among inexpensive, portable, and moving devices. IEEE 802.15.4 provides a guaranteed time slot (GTS) mechanism to allocate a specific duration within a superframe for time-critical transmissions. This paper proposes an adaptive GTS allocation (AGA) scheme for IEEE 802.15.4, which considers low latency and fairness. The scheme is designed based on the existing IEEE 802.15.4 medium access control protocol, and IEEE 802.15.4 devices can receive this AGA service without any modification. A simulation model and an analytical model are developed to investigate the performance of our AGA scheme. The numerical results show that the proposed scheme significantly outperforms the existing IEEE 802.15.4 implementation.     

High Performance Wireless Switch Protocol for IEEE 802.11 Wireless Networks

All mobile stations (STAs) in IEEE 802.11 infrastructure wireless local area networks (IWLAN) are coordinated by an access point (AP). Within the 2.4 GHz unlicensed industry, science, and medicine (ISM) band defined in the IEEE 802.11 2.4 GHz physical layer (PHY) specifications, three channels are available for concurrently transferring data packets at the coverage area of an AP. In most of small/medium enterprises or home environments, an AP with one selected channel is sufficient for covering whole service area, but this implies that the radio resources for the remaining two channels are wasted. In order to overcome the drawback, we propose a new and simple media access control (MAC) protocol, named wireless switch protocol (WSP), for increasing the throughput of IEEE 802.11 IWLAN network to support high quality multimedia traffic. This is achieved by allowing any pair of STAs in IWLAN to exchange data packets in one of other idle channels after their handshake with each other in the common channel controlled by AP. Simulation results show that the total network throughput of WSP depends on the time taken by channel switching, and on the ‘Intranet’ and ‘Internet’ traffic distribution, where the Intranet and Internet mean data transmission between STAs in IWLAN and between the STA and wired host, respectively. When all data packets are Intranet traffic and the traffic load is heavy, the ratio of Goodput for the proposed WSP to that of IEEE 802.11 standard approximates 400%. In the worse case of all Internet traffic, the proposed WSP still obtains the similar throughput as that of IEEE 802.11 standard.Jenhui Chen was born on October 12, 1971 in Taipei, Taiwan, Republic of China. He received the Bachelor’s and Ph.D. degree in Computer Science and Information Engineering (CSIE) from Tamkang University in 1998 and 2003, respectively. In the Spring of 2003, he joined the faculty of Computer Science and Information Engineering Department at Chang Gung University and served as the Assistant Professor. He occupies the supervisor of Network Department in the Information Center, Chang Gung University. Dr. Chen once served the reviewer of IEEE Transactions on Wireless Communications, ACM/Kluwer Mobile Networks and Applications (MONET), and Journal of Information Science and Engineering. His main research interests include design, analysis, and implementation of communication and network protocols, wireless networks, milibots, and artificial intelligence. He is a member of ACM and IEEE.Ai-Chun Pang was born in Hsinchu, Taiwan, R.O.C., in 1973. She received the B.S., M.S. and Ph.D. degrees in Computer Science and Information Engineering from National Chiao Tung University (NCTU) in 1996, 1998 and 2002, respectively. She joined the Department of Computer Science and Information Engineering, National Taiwan University (NTU), Taipei, Taiwan, as an Assistant Professor in 2002. Her research interests include design and analysis of personal communications services network, mobile computing, voice over IP, and performance modeling.Shiann-Tsong Sheu received his B.S. degree in Applied Mathematics from National Chung Hsing University in 1990, and obtained his Ph.D. degree in Computer Science from National Tsing Hua University in May of 1995. From 1995 to 2002, he was an Associate Professor at the Department of Electrical Engineering, Tamkang University. Since Feb. 2002, he has become a Professor at the Department of Electrical Engineering, Tamkang University. Dr. Sheu received the outstanding young researcher award by the IEEE Communication Society Asia Pacific Board in 2002. His research interests include next-generation wireless communication, WDM networks and intelligent control algorithms.Hsueh-Wen Tseng received his B.S. degree in electrical engineering from Tamkang University, Taipei country, Taiwan, in 2001 and M.S. degree in electrical engineering from National Taiwan University of Science and Technology, Taipei, Taiwan, in 2003. He is currently pursuing the Ph. D. degree at the Department of Computer Science and Information Engineering, National Taiwan University, Taipei, Taiwan. His research interests include design, analysis and implementation of network protocols and wireless communications.     

HJ-1A/B星CCD相机在轨辐射性能检测分析

为检测分析HJ-1A/B星CCD相机在轨辐射探测性能及其辐射定标的有效性,提出了基于多种光学特性地面目标的在轨检测方法。首先,介绍了HJ-1A/B星CCD相机在轨辐射性能检测方法,并基于2013年HJ-1A/B卫星地面同步观测试验数据,获取了HJ-1A/B星过境时刻的卫星入瞳处等效辐亮度。然后以该等效辐亮度为基准,对HJ-1A/B星CCD相机历次在轨辐射定标结果进行检验,分析HJ-1A/B星CCD相机的在轨运行期间辐射探测性能变化趋势。结果表明：HJ-1A/B星在轨运行过程中,辐射性能在不断发生变化;在轨运行5年多时间里,HJ-1A/B星的CCD相机各波段的辐射性能平均衰变量最低为3.7%,最大为39.6%;为保证遥感数据的定量化精度,定期的在轨绝对辐射定标十分必要。     

Serving radio network controller relocation for UMTS all-IP network

To support real-time multimedia services in UMTS all-IP network, Third-Generation Partnership Project TR 25.936 proposed two approaches to support real-time serving radio network controller (SRNC) switching, which require packet duplication during SRNC relocation. These approaches significantly consume extra system resources. This paper proposes the fast SRNC relocation (FSR) approach that does not duplicate packets. In FSR, a packet buffering mechanism is implemented to avoid packet loss at the target RNC. We propose an analytic model to investigate the performance of FSR. The numerical results show that packet loss at the source RNC can be ignored. Furthermore, the expected number of packets buffered at the target RNC is small, which does not prolong packet delay.     

资源一号02C PMS传感器在轨场地绝对辐射定标研究

资源一号02C全色/多光谱传感器数据在国民经济建设中有着广泛的应用, 而精确的绝对辐射定标系数决定着其应用的广度与深度。在轨场地定标方法是获取高精度定标系数的有效方法之一。利用敦煌辐射校正场,基于地面同步测量实验,通过两点法对资源一号 02C卫星全色/多光谱传感器进行在轨绝对辐射定标。并使用新疆靶标2012年7月23日实测数据进行定标系数的验证工作。结果表明：利用两点法所得定标系数可靠性高,可满足遥感数据定量化应用的需要。