Performance analysis of cellular CDMA high‐speed data services

This paper investigates the forward‐link peak and average data rates, throughput, and coverage of a cellular CDMA system for delivering high‐speed wireless data services. The analysis takes into account major aspects commonly found in the forward data channel and applies the generalized Shannon capacity formula for multi‐element antenna (MEA) systems. The study focuses on the physical layer and is flexible for various propagation environments, antenna configurations, multicode allocations, user distributions, and cell site configurations. Numerical results for various multicode allocations are presented for a system model with two‐tier interfering cells operating under a frequency selective slow fading channel with propagation environments specified in the Recommendation ITU‐R M.1225. Copyright © 2006 John Wiley & Sons, Ltd.     

Seamless LTE connectivity in high‐speed trains

High‐speed train (HST) is revitalizing the train as a preferred mid‐range transportation system. The provision of broadband Internet connectivity onboard trains is one of the key challenges in the competition among train operators. Unprecedented spectral efficiency and data rates (up to 100Mbps in high mobility) of the Universal Mobile Telecommunications System long‐term evolution (LTE) are expected to offer the solution for high‐speed Internet access onboard in HSTs. Massive wireless access and frequent handovers (HOs) of a large number of users might potentially cause service interruptions, and this, in turn, degrades intolerably the quality of experience (QoE) of users' onboard Internet access. In this paper, we propose a solution based on distributed antenna system that combines directional and omni‐directional antennas as train‐to‐ground radio‐access terminals (T‐RATs) and LTE femtocells in each carriage. Directional antennas are deployed at both ends of the HST to provide multi‐cell access by diversifying the HOs over multiple LTE cells. This mechanism virtually elongates the train size by connecting the front and rear carriages' T‐RATs to the faraway eNodeBs and augmenting the number of cells the HST can be simultaneously connected to. An ad hoc distributed load‐balancing mechanism that consists in offloading backlogged packets to the on‐service T‐RATs is mandatorily paired with multi‐cell access scheme to tie up with the request of seamless onboard Internet service at high QoE level. Copyright © 2015 John Wiley & Sons, Ltd.     

Distributed radio access technology selection for adaptive networks in high‐speed,B3G infrastructures

Wireless systems migrate towards the era of ‘Beyond the 3rd Generation’ (B3G). A fundamental facilitator of this vision is the evolution of high speed, adaptive networks, needed for better handling the offered demand and improving resource utilization. Adaptive networks dynamically select their configuration, in order to optimally adapt to the changing environment requirements and conditions. This paper presents optimization functionality that can be used to support network adaptability (cognition‐reconfigurability) in a B3G context. The paper starts from the business case that justifies the need for placing research onto adaptive networks and then continues with the management functionality for (re)configuration decisions, which is targeted to the dynamic selection of the appropriate radio access technologies (RATs). RAT selection is modelled through an optimization problem called (RAT, Demand and QoS‐Assignment problem—RDQ‐A), the solution of which assigns in a distributed manner the available RATs to adaptive Base Station transceivers and the demand (users) to these transceivers and to QoS levels, respectively. The RDQ‐A optimization problem is decoupled in several sub‐problems and is implemented in phases corresponding to the aforementioned assignments, while efficient custom greedy algorithms are mobilized in each phase for obtaining the optimum assignment. Finally, indicative results from the application of the proposed functionality to a simulated network are presented. Copyright © 2006 John Wiley & Sons, Ltd.     

Loss characterization in high-speed networks through simulation of fluid models

This paper describes the design principles of a fluid-based, discrete-event simulator and its application to the characterization of losses in ATM networks. This simulation technique allows us to obtain performance measures that either cannot be found using known analytical methods or for which a conventional simulation is too expensive; notably, fluid-model simulation makes it feasible to characterize for a given buffer its occupation, duration of congestion periods, frequency of loss bursts and loss-burst volume in fairly complex networks. Several numerical examples illustrate the proposed simulation method.     

Probabilistic response‐time analysis for real‐time systems in body area sensor networks

Advances in real‐time system and wireless communication have led to the deployment of body area sensor networks (BASNs) for effective real‐time healthcare applications. Real‐time systems in BASNs tend increasingly to be probabilistic and mixed critical to meet stringent requirements on space, weight, and power consumption. Response‐time analysis is an important and challenging task for BASNs to provide some critical services. In this paper, we propose a request‐based compositional probabilistic response‐time analysis framework for probabilistic real‐time task models with fixed‐priority preemptive scheduling in BASNs. In this method, each probabilistic real‐time task is abstracted as a probabilistic request function. Rough response‐time distribution is computed first based on the cumulative request distribution and then exact response‐time distribution is obtained by refinement based on the request increase distribution. Our strategy can effectively improve performance by reducing repetitive computational overhead for the probabilistic response‐time analysis of all tasks in the system. Our evaluation demonstrates that our proposed method significantly outperforms the existing probabilistic response‐time analysis algorithm in terms of analysis duration. Copyright © 2015 John Wiley & Sons, Ltd.     

Admission control and handover management for high‐speed trains in vehicular geostationary satellite networks with terrestrial gap‐filling

Following a recent upgrade, the Digital Video Broadcasting—Return Channel Satellite (DVB‐RCS) standard sets up to support terminal mobility. In this scenario, integration with terrestrial systems becomes a primary concern to ensure network connectivity in urban areas. This article proposes an integrated satellite–terrestrial architecture for the provision of broadband services onboard high‐speed trains, in which terrestrial cellular networks are seen as viable gap‐fillers for discontinuous satellite coverage. We derive an analytical model of the hybrid DVB‐RCS‐cellular system by exploiting analogies between the mobility pattern predictability of LEO constellations and that of high‐speed trains. Terminals whose QoS cannot be guaranteed by the satellite segment are proposed to temporarily divert the connections towards the terrestrial infrastructure, where available. Using an iterative approach based on the Erlang fixed‐point approximation, we show performance improvements with respect to stand‐alone satellite systems in terms of handover failure probability and overall resource utilization. The analytical model is also validated via our ns2‐based DVB‐RCS packet‐level simulator. Detailed modelling of synchronization and signalling mechanisms confirms the accuracy of the analytical results, and shows that topology and mobility information can contribute to refine radio resource utilization optimality when used jointly. Copyright © 2009 John Wiley & Sons, Ltd.     

Multi‐carrier platform for wireless communications. Part 2: OFDM and MC‐CDMA systems with high‐performance,high‐throughput via innovations in spreading

Multi‐carrier technologies in general, and OFDM and MC‐CDMA in particular, are an integral part of the wireless landscape. In this second part of a two‐part survey, the authors present an innovative set of spreading codes known as CI codes, and demonstrate how these significantly increase performance and capacity in OFDM and MC‐CDMA systems, all the while eliminating PAPR concerns. Regarding OFDM: the spreading of each symbol over all N carriers using CI spreading codes (replacing the current one symbol per carrier strategy) are presented. CI codes are ideally suited for spreading OFDM since, when compared to traditional OFDM, CI‐based OFDM systems achieve the performance of coded OFDM (COFDM) while maintaining the throughput of uncoded OFDM, and, at the same time, eliminate PAPR concerns. When applied to MC‐CDMA, CI codes provide a simple means of supporting 2N users on N carriers while maintaining the performance of an N‐user Hadamard Walsh code MC‐CDMA system, i.e., CI codes double MC‐CDMA network capacity without loss in performance. The CI codes used in OFDM and MC‐CDMA systems are directly related to the CI pulse (chip) shapes used to enhance TDMA and DS‐CDMA (see part 1): hence, the CI approach provides a common hardware platform for today's multi‐carrier/multiple‐access technologies, enabling software radio applications. Copyright © 2002 John Wiley & Sons, Ltd.     

Analysis and enhancement of multi‐channel MAC protocol for ad hoc networks

In this paper, an analytical model is proposed to calculate the network throughput of dedicated control channel protocols that are designed to schedule multiple packets to be transmitted on different data channels simultaneously. Based on the analytical model, a scheme by tuning the initial contention window size is proposed to maximize the network throughput. We also present a novel multi‐channel MAC protocol for single‐hop scenario. Simulation results show that the proposed model is capable of modeling the behaviors of dedicated control channel protocols accurately. Furthermore, the proposed scheme can reduce the cost of collisions and enhance the network throughput up to 22% for 1 kB packet size and 80 nodes. Compared with other dedicated control channel protocols, the proposed protocol can schedule more control packets and use multiple channels more efficiently. Copyright © 2010 John Wiley & Sons, Ltd.     

高速移动条件下相移键控解调的设计与仿真

相移键控调制技术具有较高带宽利用率、优良的抗噪声性能等特点,在高速数据传输率的遥测系统中具有广泛的应用。针对高速移动条件下采用相移键控调制方法的遥测系统,采用多普勒频移进行估计和校正方法,对遥测系统中的解调技术进行设计与仿真。首先,介绍多普勒频偏对相移键控调制方式的影响。其次,对于常用的四相相移键控和八相相移键控调制和解调技术进行讨论。最后,通过对高速移动条件下遥测接收系统的仿真结果对比,验证了文中所提方法的可行性。     

Performance analysis of channel estimation in amplify‐and‐forward multi‐hop direct forwarding wireless networks

In this paper, we study the performance of a training‐based least square (LS) and linear minimum mean‐square‐error (LMMSE) channel estimation for both hop‐by‐hop and multi‐hop direct forwarding wireless sensor networks over frequency‐selective fading channels. Specifically, to investigate the properties of the channel estimation, we accomplish a theoretical analysis of MSE in terms of various link parameters. From the performance evaluation, we analytically present the effects of the number of hops on the MSE performance for channel estimations in both multi‐hop networks. Interesting observations of MSE behaviors under various conditions are discussed, and the receiver complexity and channel equalization performance are also analyzed. Finally, through the computer simulations, the analytical results and detection performance are demonstrated. Copyright © 2014 John Wiley & Sons, Ltd.     

Analytical characterization of cache replacement policy impact on content delivery time in information‐centric networks

Information‐centric networking (ICN) has emerged as a promising candidate for designing content‐based future Internet paradigms. ICN increases the utilization of a network through location‐independent content naming and in‐network content caching. In routers, cache replacement policy determines which content to be replaced in the case of cache free space shortage. Thus, it has a direct influence on user experience, especially content delivery time. Meanwhile, content can be provided from different locations simultaneously because of the multi‐source property of the content in ICN. To the best of our knowledge, no work has yet studied the impact of cache replacement policy on the content delivery time considering multi‐source content delivery in ICN, an issue addressed in this paper. As our contribution, we analytically quantify the average content delivery time when different cache replacement policies, namely, least recently used (LRU) and random replacement (RR) policy, are employed. As an impressive result, we report the superiority of these policies in term of the popularity distribution of contents. The expected content delivery time in a supposed network topology was studied by both theoretical and experimental method. On the basis of the obtained results, some interesting findings of the performance of used cache replacement policies are provided.     

Architecture design,performance analysis and VLSI implementation of a reconfigurable shared buffer for high‐speed switch/router

Modern switches and routers require massive storage space to buffer packets. This becomes more significant as link speed increases and switch size grows. From the memory technology perspective, while DRAM is a good choice to meet capacity requirement, the access time causes problems for high‐speed applications. On the other hand, though SRAM is faster, it is more costly and does not have high storage density. The SRAM/DRAM hybrid architecture provides a good solution to meet both capacity and speed requirements. From the switch design and network traffic perspective, to minimize packet loss, the buffering space allocated for each switch port is normally based on the worst‐case scenario, which is usually huge. However, under normal traffic load conditions, the buffer utilization for such configuration is very low. Therefore, we propose a reconfigurable buffer‐sharing scheme that can dynamically adjust the buffering space for each port according to the traffic patterns and buffer saturation status. The target is to achieve high performance and improve buffer utilization, while not posing much constraint on the buffer speed. In this paper, we study the performance of the proposed buffer‐sharing scheme by both a numerical model and extensive simulations under uniform and non‐uniform traffic conditions. We also present the architecture design and VLSI implementation of the proposed reconfigurable shared buffer using the 0.18 µm CMOS technology. Our results manifest that the proposed architecture can always achieve high performance and provide much flexibility for the high‐speed packet switches to adapt to various traffic patterns. Furthermore, it can be easily integrated into the functionality of port controllers of modern switches and routers. Copyright © 2008 John Wiley & Sons, Ltd.     

Performance evaluation for single‐ and semi‐layer multistage interconnection networks servicing multicast traffic by full multicast operation

Here a novel analytical method for performance prediction estimation of single‐ and multi‐layer multistage interconnection networks (MINs) under multicast environments is presented. The ‘Cell Replication While Routing’ is used as a packet routing technique and the ‘full multicast’ mode as transmission policy is employed in all the MINs under study. This model is developed for single‐layer MINs and is extended and applied to special types of multi‐layer MINs, called semi‐layer MINs, which support mixed traffic patterns such as unicast and multicast in uniform traffic conditions. The results confirm the significant performance saturation of single‐layer MINs and the improvement of corresponding performance indicators by semi‐layer MINs. The proposed analytical framework is anticipated to be a very useful tool in evaluating the performance of semi‐layer MINs in designing more efficient QoS networks. Copyright © 2010 John Wiley & Sons, Ltd.     

Scalable Approach to Failure Analysis of High‐Performance Computing Systems

Failure analysis is necessary to clarify the root cause of a failure, predict the next time a failure may occur, and improve the performance and reliability of a system. However, it is not an easy task to analyze and interpret failure data, especially for complex systems. Usually, these data are represented using many attributes, and sometimes they are inconsistent and ambiguous. In this paper, we present a scalable approach for the analysis and interpretation of failure data of high‐performance computing systems. The approach employs rough sets theory (RST) for this task. The application of RST to a large publicly available set of failure data highlights the main attributes responsible for the root cause of a failure. In addition, it is used to analyze other failure characteristics, such as time between failures, repair times, workload running on a failed node, and failure category. Experimental results show the scalability of the presented approach and its ability to reveal dependencies among different failure characteristics.     

高速电路印制板设计中的信号完整性分析——基于PROTEL99se

介绍PROTEL99se的信号完整性分析功能和高速电路的特点，并介绍PROTEL99se在高速电路印刷板设计中的应用。     

Performance analysis of selective cooperation in amplify‐and‐forward relay networks over identical Nakagami‐m channels

In cooperative communications, multiple relays between a source and a destination can increase the diversity gain. Because all the nodes must use orthogonal channels, multiple‐relay cooperation becomes spectrally inefficient. Therefore, a bestrelay selection scheme was recently proposed. In this paper, we analyzed the performance of this scheme for a system with the relays operating in amplify‐and‐forward mode over identical Nakagami‐m channels using an exact source–relay–destination signal‐to‐noise ratio (SNR).We derived accurate closed‐form expressions for various system parameters including the probability density function of end‐to‐end SNR, the average output SNR, the bit error probability, and the channel capacity. The analytical results were verified through Monte Carlo simulations. Copyright © 2011 John Wiley & Sons, Ltd.     

On the characteristics of routing paths and the performance of routing protocols in vehicle‐formed mobile ad hoc networks on highways

Recently, intelligent transportation systems (ITS) is becoming an important research topic. One goal of ITS is to exchange information among vehicles in a timely and efficient manner. In the ITS research community, inter‐vehicle communications (IVC) is considered a way that may be able to achieve this goal. An information network built on the top of vehicles using IVC can be viewed as a type of mobile ad hoc networks (MANETs). In the past, several unicast routing protocols for MANET have been proposed. However, most of them are designed for general MANETs rather than for IVC networks. In this paper, we first used more realistic vehicle mobility traces generated by a microscopic traffic simulator (VISSIM) to understand the characteristics of routing paths in an IVC network. Based on the insights gained from the derived path characteristics, we designed and implemented an intelligent flooding‐based routing protocol for small‐scale IVC networks. Via several field trials conducted on highways, we compared the performance of ad hoc on‐demand distance vector (AODV) and our protocol. Our experimental results show that (1) our protocol outperforms AODV greatly in IVC networks and (2) our protocol can provide text, image, audio, and video services for small‐scale IVC networks (e.g., a platoon) quite well. Copyright © 2009 John Wiley & Sons, Ltd.     

Joint consideration of energy‐efficiency and coverage‐preservation in microsensor networks

This paper presents an energy‐efficient and coverage‐preserving communication protocol which distributes a uniform energy load to the sensors in a wireless microsensor network. This protocol, called Distance‐based Segmentation (DBS), is a cluster‐based protocol that divides the entire network into equal‐area segments and applies different clustering policies to each segment to (1) reduce total energy dissipation and (2) balance the energy load among the sensors. Therefore, it prolongs the lifetime of the network and improves the sensing coverage. Moreover, the proposed routing protocol does not need any centralized support from a certain node which is at odds with aiming to establish a scalable communication protocol. Results from extensive simulations on two different network configurations show that by lowering the number of wasteful transmissions in the network, the DBS can achieve as much as a 20% reduction in total dissipated energy as compared with current cluster‐based protocols. In addition, this protocol is able to distribute energy load more evenly among the sensors in the network. Hence, it yields up to a 66% increase in the useful network lifetime. According to the simulation results, the sensing coverage degradation of the DBS is considerably slower than that of the other cluster‐based protocols. Copyright © 2009 John Wiley & Sons, Ltd.     

NS2的Ad hoc网络AODV协议的仿真

无线Ad hoc网络作为一种典型的自组织网络,其路由协议一直是研究的重点。以仿真AODV（Adhocon．demand distancevector）协议为例介绍了NS2仿真路由协议的详细步骤,给出了仿真结果图和一些性能分析。结果表明,对路由协议性能影响最大的是数据源的发送频率。     

Operational performance of grid‐connected PV systems on buildings in Germany

This paper presents operational performance results of grid‐connected PV systems in Germany, as collected and elaborated for the Photovoltaic Power Systems Programme (PVPS) of the International Energy Agency (IEA). Performance ratios obtained from 235 PV installations in Germany and from 133 PV plants in other countries are compared and discussed. For Germany, a significant rise in PV system performance and reliability was observed for new PV installations due to higher component efficiencies (e.g., inverter) and increased availabilities. There is a lack of long‐term experience in performance and reliability of PV systems, owing to the absence of monitoring programmes. As an outcome of IEA PVPS collaborative work, Task 2 provides reliable and worldwide monitoring performance data and results (www.task2.org). Technical and operational data is available for system planning and comparison, for teaching and training purposes as well as for future developments of financing schemes (e.g., feed‐in‐tariffs) in order to stimulate the PV market. Copyright © 2004 John Wiley & Sons, Ltd.