Vol. 66, n° 11-12, November-December 2011
Content available on Springerlink
A simplified approach to modeling the interaction between grounding grid and lightning stroke
Basma Harrat1, Bachir Nekhoul1, Kamal Kerroum2 and Khalil El Khamlichi Drissi2
1 University of Jijel, Algeria
2 University Blaise Pascal, Aubière, France
Abstract In this work, a new approach for the modeling of the interaction between grounding grid and lightning stroke is described. We treat the case of direct and indirect effects of lightning strike. In the case of direct impact, we inject in point of grounding system a current with bi-exponential wave shape and we calculate the distribution of potentials and currents on the grid and the electromagnetic field it will emit. For the second case, we treat a problem of electromagnetic coupling, which is to calculate the induced currents that developed on the grounding grid when this later is illuminated by a lightning channel located in its vicinity. The presented model is validated by comparing the obtained results to the results arising from the full wave (antenna) model available in literature and to the results obtained by using NEC4 software. The principal advantage of the presented approach is the simplicity of the implementation providing a direct determination of the both current and potential distribution along the grounding grid and the related electromagnetic field in an arbitrary point in the air and/or soil, as well.
Keywords Grounding system – Interaction – EM field – Lightning stroke – Modeling
M-correlated sweeps performance analysis of adaptive detection of radar targets in interference-saturated environments
Mohamed B. El Mashade
Al Azhar University, Cairo, Egypt
Abstract Our scope in this paper is to analyze the performance of a radar signal processor that consists of a nonrecursive MTI followed by a square-law integrator and a CFAR circuit detection, the operation of which is based on the double-threshold procedure. The processor performance is evaluated for the case where the background environment is assumed to be ideal (homogeneous) as well as in situation where it contains a number of interferers along with the target under test (multitarget environment). For some specified values for the first threshold, it is shown that the processor detectability loss is very low, and the performance degradation, caused by spurious targets is quite small even if their number is large. Additionally, the processor performance improves as either the number of incoherently integrated pulses increases or the correlation between consecutive sweeps decreases, as we predict.
Keywords CFAR detection – Moving target indicator (MTI) – Noise and clutter – Double-threshold processor – Incoherent integration – Multiple-target environments
A combined approach for detecting hidden nodes in 802.11 wireless LANs
Palestine Polytechnic University, Hebron, Palestine
Abstract Hidden node is a fundamental problem that severely degrades the performance of wireless networks. The problem occurs when nodes that do not hear each other transmit at the same time, which leads to data packet collision. IEEE 802.11 Wireless Local Area Networks (WLANs) tries to solve this problem through the Request to Send/Clear to Send (RTS/CTS) mechanism. However, the mechanism is not wholly successful. The RTS/CTS idea is based on the assumption that all nodes in the vicinity of Access Points will hear CTS packets and consequently defer their transmissions. The shortcoming of RTS/CTS stems from the fact that such packets introduce high overhead if extensively used. In this article, we propose a hybrid approach for detecting hidden nodes in 802.11 WLANs. The approach is mainly based on adaptive learning about collisions in the network. We think that the approach will be useful for controlling the tuning of RTS/CTS threshold and therefore reduce the overhead those packets introduce. Detailed simulation experiments have shown the strength of the proposed approach compared with other approaches.
Keywords WLANs – Hidden nodes detection – 802.11
Reactive routing evaluation using modified 802.11a with realistic vehicular mobility
Muhammad Azhar Iqbal, Furong Wang, Xie Xu, Sarah M. Eljack and Ahmad H. Mohammad
Huazhong University of Science and Technology, Wuhan, China
Abstract Realistic mobility dynamics and underlying PHY/MAC layer implementation affect real deployment of routing protocols in vehicular ad hoc network (VANET). Currently, dedicated short range communication devices are using wireless access in vehicular environment (WAVE) mode of operation, but now IEEE is standardizing 802.11p WAVE. This work presents an in-depth simulation-based analysis of two reactive routing protocols, i.e., dynamic source routing (DSR) and ad hoc on-demand distance vector (AODV) with modified IEEE 802.11a PHY/MAC layers (comparable to 802.11p) in modified VANET mobility models (freeway, stop sign, and traffic sign) in terms of load, throughput, delay, number of hops, and retransmission attempts. Results obtained using OPNET simulator show that in urban/highway mobility scenarios, AODV’s performance with forthcoming 802.11p at high bit rate would be better than DSR in terms of high throughput, less delay, and retransmission attempts. Moreover, this comprehensive evaluation will assist to address challenges associated with future deployment of routing protocols integrated upon devices with upcoming IEEE 802.11p, concerning specific macro-/micro-mobility scenarios.
Keywords VANET – AODV – DSR – IEEE 802.11p – Mobility models – DSRC – Routing analysis
An ID-based proxy signature schemes without bilinear pairings
He Debiao, Chen Jianhua and Hu Jin
Wuhan University, China
Abstract The proxy signature schemes allow proxy signers to sign messages on behalf of an original signer, a company, or an organization. Such schemes have been suggested for use in a number of applications, particularly in distributed computing, where delegation of rights is quite common. Many identity-based proxy signature schemes using bilinear pairings have been proposed. But the relative computation cost of the pairing is approximately twenty times higher than that of the scalar multiplication over elliptic curve group. In order to save the running time and the size of the signature, in this letter, we propose an identity-based signature scheme without bilinear pairings. With the running time being saved greatly, our scheme is more practical than the previous related schemes for practical application.
Keywords Digital signature – Identity-based proxy signature – Bilinear pairings – Elliptic curve
A novel authenticated group key agreement protocol for mobile environment
National Taiwan University os Science and Technology, Taipei, Taiwan
Abstract An authenticated group key agreement protocol allows a group of parties to authenticate each other and then determine a group key via an insecure network environment. In 2009, Lee et al. first adopted bilinear pairings to propose a new nonauthenticated group key agreement protocol and then extend it to an authenticated group key agreement protocol. This paper points out that the authenticated protocol of Lee et al. is vulnerable to an impersonation attack such that any adversary can masquerade as a legal node to determine a group key with the other legal nodes and the powerful node. This paper shall employ the short signature scheme of Zhang et al. to propose a new authenticated group key agreement protocol. The short signature scheme of Zhang et al. is proven to be secure against the adaptive chosen-message attacks in the random oracle model, so the proposed protocol can withstand the possible attacks. Besides, compared with the authenticated protocol of Lee et al., the proposed protocol is more secure and efficient.
Keywords Authenticated group key – Bilinear pairings – Impersonation attack – Short signature – Random oracle
An energy-efficient MAC protocol based on IEEE 802.11 in wireless ad hoc networks
Chien-Min Wu1, Yi-Ching Liaw1, Maw-Lin Leou1 and Hui-Kai Su2
1 Nanhua University, Taiwan
2 National Formosa University, Taiwan
Abstract Energy efficiency is a measure of the performance of IEEE 802.11 wireless multihop ad hoc networks. The IEEE 802.11 standard, currently used in wireless multihop ad hoc networks, wastes bandwidth capacity and energy resources because of many collisions. Therefore, controlling the contention window size at a given node will increase not only the operating life of the battery but also the overall system capacity. It is essential to develop effective backoff schemes for saving power in IEEE 802.11 wireless multihop ad hoc networks. In this paper, we propose an energy-efficient backoff scheme and evaluate its performance in an ad hoc network. Our contention window mechanism devised by us grants a node access to a channel on the basis of the node’s percentage of residual energy. We use both an analytical model and simulation experiments to evaluate the effective performance of our scheme in an ad hoc network. Our extensive ns-2-based simulation results have shown that the proposed scheme provides excellent performance in terms of energy goodput, end-to-end goodput, and packet delivery ratio, as well as the end-to-end delay.
Keywords IEEE 802.11 – Contention window mechanism – Ad hoc networks – ns-2 – Energy goodput
Improving the multiple access method of home networks over the electrical wiring
Miguel Elias Mitre Campista, Luís Henrique M. K. Costa and Otto Carlos M. B. Duarte
Universidade Federal do Rio de Janeiro, Brazil
Abstract Data communications on domestic low-voltage powerlines benefit from an ubiquitous and already existent infrastructure. Nevertheless, high-speed communications on this environment faces obstacles such as attenuation and noise. The HomePlug standard defines Media Access Control (MAC)- and physical (PHY)-layer protocols for home electrical wiring networks. Its MAC protocol has introduced the deferral counter (DC) mechanism, which adapts the contention of the nodes for the medium according to the network load. This article proposes the Contention window Pro-active Increase (CPI) mechanism to enhance the performance of HomePlug. The CPI mechanism is based on DC and improves the HomePlug efficiency by faster increasing the contention window size. As a consequence, there are fewer collisions and the aggregated throughput increases. Under high network load, our simulation results show a tradeoff concerning throughput and jitter. CPI improves HomePlug throughput by up to 3% with no jitter increase and by up to 15% at the cost of additional jitter.
Keywords Home networks – HomePlug – Medium access control – CPI mechanism
Performance analysis of HARQ protocols with link adaptation on fading channels
Télécom Bretagne, Brest, France
Abstract This work considers hybrid automatic repeat request (HARQ) protocols on a fading channel with Chase combining and deals with both Rayleigh and Nakagami-m fading. We derive the packet loss probability and the throughput for HARQ both for a slow-varying and a fast-varying channel. We then consider link adaptation with complete channel state information (CSI) for which the instantaneous signal-to-noise ratio (SNR) is known and with incomplete CSI for which only the average SNR is known. We derive analytical formulae of the long-term throughput. These formulae are simple enough to be used for higher level simulations. We show that the throughput is slightly higher on a slow-varying channel but at the expense of a higher loss probability.
Keywords Hybrid automatic repeat request – Adaptive modulation and coding – Cross-layer design – Wireless networks – Fading channels