ISRN Communications and Networking The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Design of an Aperture-Coupled Frequency-Reconfigurable Microstrip Stacked Array Antenna for LTE and WiMAX Applications Sun, 01 Jun 2014 11:54:29 +0000 The aim of this paper is to design a novel structure of a frequency-reconfigurable microstrip array antenna by using a combination of aperture-coupled and the stacked patch technology. The four sets of two different aperture slot shapes (I-shaped and H-shaped) are printed on the ground and are functional to transfer the wave and the signal to the selected radiating layers. Both aperture slot positions are based on the bottom patches (layer 2) and top patches (layer 1), respectively. To achieve the frequency reconfigurability, four PIN diode switches are integrated on the feed line layer positioned between both aperture slots on the ground. The activation of the selected patches will determine the current operating frequency of the proposed antenna. A 2.6 GHz or 3.5 GHz frequency is achieved by switching all the PIN diode switches to ON or OFF mode synchronously. The advantage of the proposed antenna is that it can minimize the usage of the antenna’s surface area, with different size of the patch having different operating frequencies, sorted in different layer. The measured results of the return losses, radiation patterns, and the practical indoor propagation measurement achieved good agreement with the simulated results. N. Ramli, M. T. Ali, M. T. Islam, A. L. Yusof, S. Muhamud-Kayat, and A. A. Azlan Copyright © 2014 N. Ramli et al. All rights reserved. A Traffic Cluster Entropy Based Approach to Distinguish DDoS Attacks from Flash Event Using DETER Testbed Tue, 13 May 2014 10:38:34 +0000 The detection of distributed denial of service (DDoS) attacks is one of the hardest problems confronted by the network security researchers. Flash event (FE), which is caused by a large number of legitimate requests, has similar characteristics to those of DDoS attacks. Moreover DDoS attacks and FEs require altogether different handling procedures. So discriminating DDoS attacks from FEs is very important. But the research involving DDoS detection has not laid enough emphasis on including FEs scenarios in the experiments. In this paper, we are using traffic cluster entropy as detection metric not only to detect DDoS attacks but also to distinguish DDoS attacks from FEs. We have validated our approach on cyber-defense technology experimental research laboratory (DETER) testbed. Different emulation scenarios are created on DETER using mix of legitimate, flash, and different types of attacks at varying strengths. It is found that, when flash event is triggered, source address entropy increases but the corresponding traffic cluster entropy does not increase. However, when DDoS attack is launched, traffic cluster entropy also increases along with source address entropy. An analysis of live traces on DETER testbed clearly manifests supremacy of our approach. Monika Sachdeva and Krishan Kumar Copyright © 2014 Monika Sachdeva and Krishan Kumar. All rights reserved. Systematic Review of Multiple Contents Synchronization in Interactive Television Scenario Wed, 19 Mar 2014 13:21:28 +0000 Context. Interactive TV has not reached yet its full potential. How to make the use of interactivity in television content viable and attractive is something in evolution that can be seen with the popularization of new approaches as the use of second screen as interactive platform. Objective. This study aims at surveying existing research on Multiple Contents TV Synchronization in order to synthesize their results, classify works with common points, and identify needs for future research. Method. This paper reports the results of a systematic literature review and mapping study on TV Multiple Contents Synchronization published until middle 2013. As result, a set of 68 papers was generated and analyzed considering general information such as sources and time of publication; covered research topics; and synchronization aspects such as methods, channels, and precision. Results. Based on the obtained data, the paper provides a high level overview of the analyzed works; a detailed exploration of each used and proposed technique and its applications; and a discussion and proposal of a scenario overview and classification scheme based on the extracted data. Ricardo Mendes Costa Segundo and Celso Alberto Saibel Santos Copyright © 2014 Ricardo Mendes Costa Segundo and Celso Alberto Saibel Santos. All rights reserved. Investigation on Mutual Contention Bandwidth Request Mechanisms in Two-Hop Relay Network with ITU-R Path Loss Models Wed, 29 May 2013 18:45:23 +0000 The performance of two-hop contention based bandwidth request (BR) mechanism for WiMAX relay networks is investigated under ITU-R path loss models. In conventional WiMAX systems, the mobile stations (MS) update their contention window irrespective of their transmission failures. Those systems update their contention window on collision and due to channel error or unavailability of bandwidth. Further, these failure models have been suggested for single hop networks. The failure model in two-hop systems becomes complex since it may include additional failure events such as improper detection of codes and channel error due to varying path loss. Interestingly, these failure events (collision, channel error, unavailability of bandwidth, and improper detection of codes) do not occur evenly for both hops of a link. Hence, to set the contention window effectively, unique failure models are developed by considering the characteristics of BR mechanism and hop at which the BR is performed. In the proposed system, the two-hop BR is carried out with all combinations of message and code bandwidth request schemes. Among them, the message-code BR mechanism performs better under suburban fixed and outdoor to indoor or pedestrian environment, and code-code BR scheme performs better for vehicular environment. Rajesh Anbazhagan and Nakkeeran Rangaswamy Copyright © 2013 Rajesh Anbazhagan and Nakkeeran Rangaswamy. All rights reserved. Interference Mitigation through Successive Cancellation in Heterogeneous Networks Mon, 11 Mar 2013 08:17:24 +0000 We present a practical interference management scheme for heterogeneous networks (HetNets). The underlying ideas are based on (i) Han-Kobayashi-type message splitting (MS) where the receivers decode and cancel “part” of the interference which is accordingly optimized by the transmitters to ensure decoding and (ii) opportunistic interference cancellation (OIC) where the interfering transmitters act independently of the receivers that employ interference cancellation. We develop a novel transmission and reception scheme, called joint MS and OIC (MS-OIC), that engages both MS and OIC to account for a practical HetNet system with multiple macrocells and femtocells. The MS component includes a precoder design that judiciously maximizes the weighted sum throughput via the enabling of interference cancellation. A system design along with a novel scheduler that facilitates MS-OIC in a general HetNet system is also developed. System level simulations for a general HetNet system are presented, and the proposed MS-OIC scheme is compared with benchmark schemes such as Coordinated Beamforming (CBF) and joint CBF and Almost Blank Subframes (CBF-ABS). It is observed that the proposed MS-OIC scheme improves the macrocell throughput substantially, balances the achievable rates between the macrocell and femtocell users, and provides significant outage performance improvement in the system. Onur Sahin, Jialing Li, Enoch Lu, Yingxue Li, and Philip J. Pietraski Copyright © 2013 Onur Sahin et al. All rights reserved. Dual-Polarized Synthetic Antenna Array for GNSS Handheld Applications Wed, 16 Jan 2013 16:08:28 +0000 Small portable Global Navigation Satellite System (GNSS) receivers have revolutionized personal navigation through providing real-time location information for mobile users. Nonetheless, signal fading due to multipath remains a formidable limitation and compromises the performance of GNSS receivers. Antenna diversity techniques, including spatial and polarization diversity, can be used to mitigate multipath fading; however, the relatively large size of the spatially distributed antenna system required is incompatible with the small physical size constraints of a GNSS handheld receiver. User mobility inevitably results in motion of the handset that can be exploited to achieve diversity gain through forming a spatially distributed synthetic array. Traditionally, such motion has been construed as detrimental as it decorrelates the received signal undermining the coherent integration processing gain generally necessary for acquiring weak faded GNSS signals. In this paper the processing gain enhancement resulting from a dual-polarized synthetic array antenna, compatible with size constraints of a small handset that takes advantage of any user imposed motion, is explored. Theoretical analysis and experimental verifications attest the effectiveness of the proposed dual-polarized synthetic array technique by demonstrating an improvement in the processing gain of the GNSS signal acquisition operation. V. Dehghanian, A. Broumandan, M. Zaheri, and J. Nielsen Copyright © 2013 V. Dehghanian et al. All rights reserved. An Overview of Algorithms for Network Survivability Wed, 05 Dec 2012 13:57:40 +0000 Network survivability—the ability to maintain operation when one or a few network components fail—is indispensable for present-day networks. In this paper, we characterize three main components in establishing network survivability for an existing network, namely, (1) determining network connectivity, (2) augmenting the network, and (3) finding disjoint paths. We present a concise overview of network survivability algorithms, where we focus on presenting a few polynomial-time algorithms that could be implemented by practitioners and give references to more involved algorithms. F. A. Kuipers Copyright © 2012 F. A. Kuipers. All rights reserved. Network Topology Models for Multihop Wireless Networks Sat, 24 Nov 2012 10:50:24 +0000 A typical feature of huge, random network topologies is that they are too large to allow a fully detailed description. Such enormous, complex network topologies are encountered in numerous settings and have generated many research investigations. Well-known examples are the Internet and its logical overlay networks, such as the World Wide Web as well as online social networks. At the same time, extensive and rapidly growing wireless ad hoc and sensor networks also lead to hard topology modeling questions. In the current paper, we primarily focus on large, random wireless networks but also consider Web and Internet models. We survey a number of existing models that aim at describing the network topology. We also exhibit common generalizations of various sets of models that cover a number of known constructions as special cases. We demonstrate that higher levels of abstraction, despite their very general nature, can still be meaningfully analyzed and offers quite useful and unique help in solving certain hard networking problems. We believe that this research area can and will generate further significant contributions to the analysis of very large networks. András Faragó Copyright © 2012 András Faragó. All rights reserved. Evolution of Signaling Information Transmission Tue, 20 Nov 2012 15:02:26 +0000 Next Generation Network (NGN) faces the challenge of the rapidly increasing amount of signaling. The growing amount of signaling is a consequence of several reasons arising from the fact that signaling is the main source of network intelligence, analysis, and user behavior monitoring. With the increase in signaling load and complexity, the network management becomes a challenging issue that can impact overall Quality of Service (QoS). To confront this issue, there is a need for reliable and forehand signaling transmission in NGN. As there is much confusion about the interpretation of this concept, this paper aims to provide an overview of the evolution of signaling transmission. Migration towards NGN is analyzed from the signaling perspective. The NGN signaling protocols and related transmission requirements are identified. Through the discussion of standard approaches, the paper considers our previously published approach to signaling transmission along with the current issues and emerging opportunities. Jasmina Baraković Husić, Himzo Bajrić, and Sabina Baraković Copyright © 2012 Jasmina Baraković Husić et al. All rights reserved. Deployment of a Hybrid Multicast Switch in Energy-Aware Data Center Network: A Case of Fat-Tree Topology Tue, 30 Oct 2012 11:29:35 +0000 Recently, energy efficiency or green IT has become a hot issue for many IT infrastructures as they attempt to utilize energy-efficient strategies in their enterprise IT systems in order to minimize operational costs. Networking devices are shared resources connecting important IT infrastructures, especially in a data center network they are always operated 24/7 which consume a huge amount of energy, and it has been obviously shown that this energy consumption is largely independent of the traffic through the devices. As a result, power consumption in networking devices is becoming more and more a critical problem, which is of interest for both research community and general public. Multicast benefits group communications in saving link bandwidth and improving application throughput, both of which are important for green data center. In this paper, we study the deployment strategy of multicast switches in hybrid mode in energy-aware data center network: a case of famous fat-tree topology. The objective is to find the best location to deploy multicast switch not only to achieve optimal bandwidth utilization but also to minimize power consumption. We show that it is possible to easily achieve nearly 50% of energy consumption after applying our proposed algorithm. Tosmate Cheocherngngarn, Jean Andrian, and Deng Pan Copyright © 2012 Tosmate Cheocherngngarn et al. All rights reserved. Approximate Core Allocation for Large Cooperative Security Games Wed, 24 Oct 2012 09:00:04 +0000 Coalition games have been recently used for modeling a variety of security problems. From securing the wireless transmissions in decentralized networks to employing effective intrusion detection systems in large organizations, cooperation among interested parties has shown to bring significant benefits. Motivating parties to abide to a solution is, however, a key problem in bridging the gap between theoretical models and practical solutions. Benefits should be distributed among players (wireless nodes in a network, different divisions of an organization in security risk management, or organizations cooperating to fight spam), such that no group of players is motivated to break off and form a new coalition. This problem, referred to as core allocation, grows computationally very expensive with a large number of agents. In this paper, we present a novel approximate core allocation algorithm, called the bounding boxed core (BBC), for large cooperative security games in characteristic form that rely on superadditivity. The proposed algorithm is an anytime (an algorithm is called anytime if it can be interrupted at any time point during execution to return an answer whose value, at least in certain classes of stochastic processes, improves in expectation as a function of the computation time) algorithm based on iterative state space search for better solutions. Experimental results on a 25-player game, with roughly 34 million coalitions, show that BBC shrinks the 25-dimensional bounding-box to times its initial hypervolume. Saman Zonouz and Parisa Haghani Copyright © 2012 Saman Zonouz and Parisa Haghani. All rights reserved. Application of Particle Swarm Optimizer on Load Distribution for Hybrid Network Selection Scheme in Heterogeneous Wireless Networks Wed, 05 Sep 2012 08:35:48 +0000 Mobile terminal with multiradios is getting common nowadays with the presence of heterogeneous wireless networks such as 3G, WiMAX, and WiFi. That Network selection mechanism plays an important role in ensuring mobile terminals are always connected to the most suitable network. In this paper, we introduce and evaluate the performance of load distribution model to facilitate better network selection. We focus on the optimization of network resource utilization using the particle swarm optimizer (PSO) with the objective to distribute the system load according to the various conditions of the heterogeneous networks in order to achieve minimum system cost. Simulation results showed that the proposed approach outperformed the conventional iterative algorithm by a cost improvement of 7.24% for network size of 1000 mobile terminals using 10 particles. Yoke Chek Yee, Su Wei Tan, Heng Siong Lim, and Su Fong Chien Copyright © 2012 Yoke Chek Yee et al. All rights reserved. A Security Adaptation Reference Monitor for Wireless Sensor Network Thu, 23 Aug 2012 09:59:03 +0000 Security in Wireless Sensor Network has become a hot research topic due to their wide deployment and the increasing new runtime attacks they are facing. We observe that traditional security protocols address conventional security problems and cannot deal with dynamic attacks such as sinkhole dynamic behavior. Moreover, they use resources, and limit the efficient use of sensor resources and inevitably the overall network efficiency is not guaranteed. Therefore, the requirements of new security mechanisms must be addressed in a flexible manner. Indeed, there is a lack of generic security adaptation protocols to deal with extremely dynamic security conditions and performances in a context of Wireless Sensor Network where reliability is a critical criterion for many applications. This paper proposes our Security Adaptation Reference Monitor for Wireless Sensor already validated in proximity-based wireless network. It is based on an autonomic computing security looped system, which fine-tunes security means based on the monitoring of the context. Extensive simulations using agent-based approach have been conducted to verify the performance of our system in the case of sensor network in the presence of sinkhole attacks. The results clearly show that we are efficient in terms of survivability, overall network utilization, and power consumption. Tewfiq El-Maliki and Jean-Marc Seigneur Copyright © 2012 Tewfiq El-Maliki and Jean-Marc Seigneur. All rights reserved. Optimizing Virtual Private Network Design Using a New Heuristic Optimization Method Thu, 23 Aug 2012 08:13:01 +0000 In virtual private network (VPN) design, the goal is to implement a logical overlay network on top of a given physical network. We model the traffic loss caused by blocking not only on isolated links, but also at the network level. A successful model that captures the considered network level phenomenon is the well-known reduced load approximation. We consider here the optimization problem of maximizing the carried traffic in the VPN. This is a hard optimization problem. To deal with it, we introduce a heuristic local search technique called landscape smoothing search (LSS). This study first describes the LSS heuristic. Then we introduce an improved version called fast landscape smoothing search (FLSS) method to overcome the slow search speed when the objective function calculation is very time consuming. We apply FLSS to VPN design optimization and compare with well-known optimization methods such as simulated annealing (SA) and genetic algorithm (GA). The FLSS achieves better results for this VPN design optimization problem than simulated annealing and genetic algorithm. Hongbing Lian and András Faragó Copyright © 2012 Hongbing Lian and András Faragó. All rights reserved. Spectrum-Efficient Cognitive Radio Transceiver Using Multiwavelet Filters Thu, 16 Aug 2012 13:40:26 +0000 Cognitive radio (CR) transceiver that can offer adequate data rate and multiuser support for future wireless networks is a promising technology for reliable and spectrum-efficient mobile communication. Orthogonal frequency division multiplexing (OFDM) and scalar wavelet based schemes have been proposed as physical layer techniques for CR. This paper proposes multiwavelet packet-based multicarrier multiple-access scheme as an equally promising candidate for multi-user CR networks and using existing orthonormal multiwavelets, the performance of the proposed system is evaluated. It is shown that the error performance of the proposed system under frequency and phase offset conditions is comparable with existing schemes. Manju Mathew, A. B. Premkumar, and A. S. Madhukumar Copyright © 2012 Manju Mathew et al. All rights reserved. Game Theoretic Modeling of NGANs: Impact of Retail and Wholesale Services Price Variation Tue, 07 Aug 2012 11:42:56 +0000 The increasing demand for broadband access leads operators to upgrade the existing access infrastructures (or building new access network). Broadband access networks require higher investments (especially passive infrastructures such as trenches/ducts and base station towers/masts), and before making any decision it is important to analyze all solutions. The selection of the best solution requires understanding the technical possibilities and limitations of the different access technologies, as well as understanding the costs of building and operating the networks. This study analyzes the effect of asymmetric retail and wholesale prices on operators’ NPV, profit, consumer surplus, welfare, retail market, wholesale market, and so on. For that, we propose a techno-economic model complemented by a theoretic-game model. This tool identifies all the essential costs of building (and operating) access networks and performs a detailed analysis and comparison of the different solutions in various scenarios. Communities, operators/service providers, and regulators can use this tool to compare different technological solutions, forecast deployment costs, compare different scenarios, and so on, and help them in making deployment (or regulatory) decisions. The game-theory analyses give a better understanding of the competition and its effect on the business case scenarios’ economic results. João Paulo R. Pereira and Pedro Ferreira Copyright © 2012 João Paulo R. Pereira and Pedro Ferreira. All rights reserved. Key Management Schemes for Multilayer and Multiple Simultaneous Secure Group Communication Wed, 01 Aug 2012 09:03:44 +0000 Many emerging applications are based on group communication model and many group communications like multimedia distribution and military applications require a security infrastructure that provides multiple levels of access control for group members. The group members are divided into a number of subgroups and placed at different privilege levels based on certain criteria. A member at higher level must be capable of accessing communication in its own level as well as its descendant lower levels but not vice versa. In this paper we propose a key management scheme for this multilayer group communication. We achieve substantial reduction in storage and encryption cost compared to the scheme proposed by Dexter et al. We also address periodic group rekeying. Applications like scientific discussion and project management may lead to a scenario in which it is necessary to set up multiple secure groups simultaneously, and few members may be part of several secure groups. Managing group keys for simultaneous secure groups is critical. In this paper we propose a novel key management scheme for multiple simultaneous groups. R. Aparna and B. B. Amberker Copyright © 2012 R. Aparna and B. B. Amberker. All rights reserved. A Joint Channel-Network Coding Based on Product Codes for the Multiple-Access Relay Channel Tue, 17 Jul 2012 14:59:44 +0000 The multiple access relay channel with network coding has the potential to achieve diversity and improve coverage of wireless networks. Its network coding scheme provides an extra redundancy that can be used at the receiver to improve the performance of the cooperating users. This paper shows that the combination of channel coding and network coding, in the multiple access relay channel, can be seen as a product code with rows formed by the code-words of the individual channel codes of the users and columns formed by the network coding code-words. This new representation allows the use of any decoding algorithm of product codes at the receiver to decode the information data of the cooperating users. This decoding process is a complete joint channel-network decoding algorithm as it sees the combination of the two coding schemes as a single coding scheme. It also gives the possibility to use network coding schemes more powerful than conventional XOR-based network coding. The obtained results show that the proposed product-based network coding structure can improve the performance of the multiple-access relay channel without reducing its efficiency and allow a very flexible cooperation between the involved users. Tafzeel ur Rehman Ahsin and Slimane Ben Slimane Copyright © 2012 Tafzeel ur Rehman Ahsin and Slimane Ben Slimane. All rights reserved. Joint MMSE Transceiver Designs and Performance Benchmark for CoMP Transmission and Reception Wed, 13 Jun 2012 12:51:07 +0000 Coordinated Multipoint (CoMP) transmission and reception has been suggested as a key enabling technology of future cellular systems. To understand different CoMP configurations and to facilitate the configuration selection (and thus determine channel state information (CSI) feedback and data sharing requirements), performance benchmarks are needed to show what performance gains are possible. A unified approach is also needed to enable the cluster of cooperating cells to systematically take care of the transceiver design. To address these needs, the generalized iterative approach (GIA) is proposed as a unified approach for the minimum mean square error (MMSE) transceiver design of general multiple-transmitter multiple-receiver multiple-input-multiple-output (MIMO) systems subject to general linear power constraints. Moreover, the optimum decoder covariance optimization approach is proposed for downlink systems. Their optimality and relationships are established and shown numerically. Five CoMP configurations (Joint Processing-Equivalent Uplink, Joint Processing-Equivalent Downlink, Joint Processing-Equivalent Single User, Noncoordinated Multipoint, and Coordinated Beamforming) are studied and compared numerically. Physical insights, performance benchmarks, and some guidelines for CoMP configuration selection are presented. Jialing Li, Enoch Lu, and I-Tai Lu Copyright © 2012 Jialing Li et al. All rights reserved. A Systematic Approach for the Design, Fabrication, and Testing of Microstrip Antennas Using Inkjet Printing Technology Wed, 30 May 2012 13:58:55 +0000 We present a systematic approach for producing microstrip antennas using the state-of-the-art-inkjet printing technique. An initial antenna design based on the conventional square patch geometry is adopted as a benchmark to characterize the entire approach; the procedure then could be generalized to different antenna geometries and feeding techniques. For validation purposes, the antenna is designed and simulated using two different 3D full-wave electromagnetic simulation tools: Ansoft’s High Frequency Structure Simulator (HFSS), which is based on the Finite Element Method (FEM), and CST Microwave Studio, which is based on the Finite Integration Technique (FIT). The systematic approach for the fabrication process includes the optimal number of printed layers, curing temperature, and curing time. These essential parameters need to be optimized to achieve the highest electrical conductivity, trace continuity, and structural robustness. The antenna is fabricated using Inkjet Printing Technology (IJPT) utilizing Sliver Nanoparticles (SNPs) conductive ink printed by DMP-2800 Dimatix FujiFilm materials printer. Yahiea Al-Naiemy, Taha A. Elwi, Haider R. Khaleel, and Hussain Al-Rizzo Copyright © 2012 Yahiea Al-Naiemy et al. All rights reserved. A Three-Tier Architecture for User-Centric Ubiquitous Networked Sensing Tue, 22 May 2012 15:48:21 +0000 In a sensor network, sensor data are usually forwarded from sensor nodes to a database. This tight coupling between the nodes and the database has been complicating user-centric applications that traverse multiple different sensor networks. To break this coupling, thus enabling user-centric applications, we propose a three-tier architecture for ubiquitous networked sensing. Its major feature is that it contains the “core” device, which is assumed to be a terminal held by users between sensor nodes and sensor databases. This architecture supports the sensor data directly transmitted to and consumed by the core device, in addition to the classic ones that are transmitted to the sensor database first, and downloaded to the core. The major contribution of this paper are the following three-fold. First, we clarify the architecture itself. Researchers can leverage the architecture as the baseline of their development. Second, we show two types of prototype implementations of the core device. Industry is allowed to develop a new product for practical use of ambient sensing. Finally, we show a range of applications that are enabled by the architecture and indicate issues that need to be addressed for further investigation. Jin Nakazawa and Hideyuki Tokuda Copyright © 2012 Jin Nakazawa and Hideyuki Tokuda. All rights reserved. Passive and Active Reconfigurable Scan-Beam Hollow Patch Reflectarray Antennas Sun, 06 May 2012 14:50:34 +0000 The design concept of passive and active reconfigurable reflectarray antennas has been proposed and tested. The antenna elements in the array are identical hollowed patches. In the first phase of study the slots are loaded with a SMD capacitor to set the required phase shift needed for array implementation. Simulations show promising results. Mounting a SMD capacitor in such a configuration can be considered as the first step in using capacitive loading on a slotted patch for active microstrip reflectarrays. It is shown that by adjusting the capacitance values it is possible to scan the beam. In the second phase, the patch elements are loaded with active varactor-diode device which its reflected phase can be varied. This phase alteration is based on the variation of the diode capacitance which can be achieved by varying the biasing voltage of the active varactor device. In latter approach by activating these varactor devices, the phase of each antenna element in the array configuration can be adopted dynamically and consequently, its beam direction can be reconfigured. The reflectarrays incorporating passive and active elements have been built and tested at 7.0 GHz and 6.0 GHz, respectively. The performance of the proposed reconfigurable antennas is excellent, and there is good agreement between the theoretical and measurement results which pioneers design of arbitrarily reconfigurable antennas. M. Hajian, B. Kuijpers, K. Buisman, A. Akhnoukh, M. Pelk, L. C. N. de Vreede, J. Zijdeveld, L. P. Ligthart, and C. Spitas Copyright © 2012 M. Hajian et al. All rights reserved. QoSHVCP: Hybrid Vehicular Communications Protocol with QoS Prioritization for Safety Applications Tue, 17 Apr 2012 14:32:24 +0000 This paper introduces a hybrid communication paradigm for achieving seamless connectivity in Vehicular Ad hoc Networks (VANETs), wherein the connectivity is often affected by changes in the dynamic topology, vehicles’ speed, as well as the traffic density. Our proposed technique named QoS-oriented Hybrid Vehicular Communications Protocol (QoSHVCP) exploits both existing network infrastructure through a Vehicle-to-Infrastructure (V2I), as well as a traditional Vehicle-to-Vehicle (V2V) connection that could satisfy Quality-of-Service requirements. QoSHVCP is based on a V2V-V2I protocol switching algorithm, executed in a distributed fashion by each vehicle and is based on the cost function for alternative paths each time it needs to transmit a message. We utilize time delay as a performance metric and present the delay propagation rates when vehicles are transmitting high priority messages via QoSHVCP. Simulation results indicate that simultaneous usage of preexisting network infrastructure along with intervehicular communication provide lower delays, while maintaining the level of user’s performance. Our results show a great promise for their future use in VANETs. Ahmad Mostafa, Anna Maria Vegni, Talmai Oliveira, Thomas D. C. Little, and Dharma P. Agrawal Copyright © 2012 Ahmad Mostafa et al. All rights reserved. Quasi-Orthogonal Time Division Multiplexing and Its Performances in Rayleigh Fading Channels Tue, 27 Mar 2012 07:50:34 +0000 This paper proposes an efficient transmission scheme, Quasi-Orthogonal Time Division Multiplexing (QOTDM), which employs the shift orthogonal property of the pulse function with raised-cosine spectral shape, and the signal waveforms are quasi-orthogonal in time domain. Comparing to orthogonal frequency division multiplexing (OFDM), QOTDM is less sensitive to carrier frequency offset and power amplifier nonlinearities while keeping a similar spectral efficiency with OFDM due to single-carrier characteristics. QOTDM is a suitable consideration for the downlink transmission such as in satellite communications. An upper bound of sample error probability (SER) is derived to evaluate the performance of QOTDM. Comparisons of QOTDM and OFDM in Rayleigh fading channels show that the proposed QOTDM system is better than that of OFDM system in terms of bit error rate (BER) in high 𝐸𝑏/𝑁𝑜 regions. Enchang Sun, Kechu Yi, Bin Tian, and Dongying Zhang Copyright © 2012 Enchang Sun et al. All rights reserved. Improved Handset Antenna Performance via an Electrically Extended Ground Plane Sun, 25 Mar 2012 15:47:47 +0000 A novel and practical approach is presented providing improved antenna performance without enlarging the antenna or the ground plane. The approach electrically extends the ground plane using wire(s) that behave as surface metal extensions of the ground plane. The wire extensions can be accommodated within typical handset housing or as part of the stylish metal used on the handset’s exterior perimeter; hence don’t require enlargement of the device. Consequently, this approach avoids the costs and limitations traditionally associated with physically lengthening of a ground plane. Eight variations are presented and compared with baseline antenna performance. Both far-field patterns and near-field electromagnetic scans demonstrate that the proposed approach controls the electrical length of the ground plane and hence its chassis wavemodes, without negatively impacting the characteristics of the antenna. Improvements in performance of up to 56% in bandwidth at 900 MHz and up to 12% in efficiency with a reduction of up to 12% in the specific absorption rate (SAR) are achieved. An 8% increase in efficiency with a 1.3% improvement in bandwidth and a 20% reduction in SAR is achieved at 1880 MHz. Thus, improvements in bandwidth are achieved without compromising efficiency. Further, improvements at lower frequencies do not compromise performance at higher frequencies. Shirook M. Ali, Huanhuan Gu, Kelce Wilson, and James Warden Copyright © 2012 Shirook M. Ali et al. All rights reserved. Experimental Performance Evaluation of POBICOS Middleware for Wireless Sensor Networks Sat, 24 Mar 2012 16:50:38 +0000 The advances in the theory of wireless sensor networks have been remarkable during the past decades, but there is a lack of extensive experimental evaluations. In this paper we present performance-evaluation methods and results for POBICOS (platform for opportunistic behaviour in incompletely specified, heterogeneous object communities), which is an advanced middleware for wireless sensor networks (WSNs). The measurements concern energy consumption, duty cycle, and OS task profiling as well as communication characteristics such as round trip time (RTT) and throughput. In addition, a bandwidth analysis during a long-term experiment of fully functional POBICOS network and application is studied. Based on the evaluation results, power mode and data cache improvements are presented as well as CPU clock frequency optimizations. Jouni Hiltunen, Mikko Ala-Louko, and Markus Taumberger Copyright © 2012 Jouni Hiltunen et al. All rights reserved. Gain Improvement of Dual Band Antenna Based on Complementary Rectangular Split-Ring Resonator Tue, 20 Mar 2012 08:25:47 +0000 A simple and successful dual band patch linear polarized rectangular antenna design is presented. The dual band antenna is designed etching a complementary rectangular split-ring resonator in the patch of a conventional rectangular patch antenna. Furthermore, a parametric study shows the influence of the location of the CSRR particle on the radiation characteristics of the dual band antenna. Going further, a miniaturization of the conventional rectangular patch antenna and an enhancement of the complementary split-ring resonator resonance gain versus the location of the CSRR on the patch are achieved. The dual band antenna design has been made feasible due to the quasistatic resonance property of the complementary split-ring resonators. The simulated results are compared with measured data and good agreement is reported. Noelia Ortiz, Francisco Falcone, and Mario Sorolla Copyright © 2012 Noelia Ortiz et al. All rights reserved. A Radon Slantlet Transforms Based OFDM System Design and Performance Simulation under Different Channel Conditions Thu, 08 Mar 2012 09:25:10 +0000 Due to its good orthogonality, slantlet transform (SLT) is used in orthogonal frequency division multiplexing (OFDM) systems to reduce intersymbol interference (ISI) and intercarrier interference (ICI). This eliminates the need for cyclic prefix (CP) and increases the spectral efficiency of the design. Finite Radon transform (FRAT) mapper has the ability to increase orthogonality of subcarriers, is nonsensitive to channel parameters variations, and has a small constellation energy compared with conventional fast-Fourier-transform- (FFT-) based OFDM. It is also able to work as a good interleaver, which significantly reduces the bit error rate (BER). In this paper both FRAT mapping technique and SLT modulator are implemented in a new design of an OFDM system. The new structure was tested and compared with conventional FFT-based OFDM, Radon transform-based OFDM, and SLT-based OFDM for additive white Gaussian noise (AWGN) channel, flat fading channel (FFC), and multipath selective fading channel (SFC). Simulation tests were generated for different channel parameters values. The obtained results showed that the proposed system has increased the spectral efficiency, reduced ISI and ICI, and improved BER performance compared with other systems. Abbas Hasan Kattoush Copyright © 2012 Abbas Hasan Kattoush. All rights reserved. A Transmission Power Self-Optimization Technique for Wireless Sensor Networks Mon, 05 Mar 2012 13:35:19 +0000 Wireless sensor networks (WSNs) are generally used to monitor hazardous events in inaccessible areas. Thus, on one hand, it is preferable to assure the adoption of the minimum transmission power in order to extend as much as possible the WSNs lifetime. On the other hand, it is crucial to guarantee that the transmitted data is correctly received by the other nodes. Thus, trading off power optimization and reliability insurance has become one of the most important concerns when dealing with modern systems based on WSN. In this context, we present a transmission power self-optimization (TPSO) technique for WSNs. The TPSO technique consists of an algorithm able to guarantee the connectivity as well as an equally high quality of service (QoS), concentrating on the WSNs efficiency (Ef), while optimizing the transmission power necessary for data communication. Thus, the main idea behind the proposed approach is to trade off WSNs Ef against energy consumption in an environment with inherent noise. Experimental results with different types of noise and electromagnetic interference (EMI) have been explored in order to demonstrate the effectiveness of the TPSO technique. F. Lavratti, A. Ceratti, D. Prestes, A. R. Pinto, L. Bolzani, F. Vargas, C. Montez, F. Hernandez, E. Gatti, and C. Silva Copyright © 2012 F. Lavratti et al. All rights reserved. Antenna Optimization Using Multiobjective Algorithms Thu, 16 Feb 2012 10:39:12 +0000 This paper presents several applications of multiobjective optimization to antenna design, emphasizing the main general steps in this process. Specifications of antennas usually involve many conflicting objectives related to directivity, impedance matching, cross-polarization, and frequency range. These requirements induce multiobjective problems, which are formulated, solved, and analyzed here for three distinct antenna designs: a bowtie antenna for ground-penetrating radars, a reflector antenna for satellite broadcast systems, and a meander-line antenna for radio-frequency identification tags. Both stochastic and deterministic methods are considered in the analysis. X. L. Travassos, D. A. G. Vieira, and A. C. Lisboa Copyright © 2012 X. L. Travassos et al. All rights reserved.