Open Topics

Vol. 67, n° 5-6, May-June 2012

Content available on Springerlink

Multi-radio multi-channel routing metrics in IEEE 802.11s based wireless mesh networks

Sana Ghannay1, Sonia Mettali Gammar1, Fethi Filali2 and Farouk Kamoun1
National School of Computer Sciences, La Manouba, Tunisia
2 QU Wireless Innovations Center, Doha, Qatar

Abstract IEEE 802.11s is one of the emerging standards designed to build wireless mesh networks which may serve to extend the coverage of access networks. The default IEEE 802.11s path selection protocol Hybrid Wireless Mesh Protocol (HWMP) is based on the radio-aware airtime link metric (ALM) that outperforms the hop-count metric in single channel multi-hop wireless networks. However, this metric may lead to capacity degradation when multiple channels and/or multi-radio are used. To fully exploit the capacity gain of multiple channels use, new routing metrics have been proposed such as weighted cumulative expected transmission time, metric of interference and channel switching, interference aware routing metric, exclusive expected transmission time, and normalized bottleneck link capacity. These metrics distribute the data traffic load among channels and/or radios to reach the final destination. In this paper, we provide a qualitative comparison study that considers the characteristics of these metrics. Indeed, we substitute ALM by these different metrics, and we evaluate the performance of HWMP through simulation. Obtained results allow us to identify the appropriate use case of each metric.

Mesh networks – IEEE 802.11s – Routing metrics – Multi-channel – Multi-radio

Combinatorial double-sided auctions for network bandwidth allocation: a budget-balanced and decentralized approach

Hoang-Hai Tran1 and Bruno Tuffin2
Alcatel-Lucent INRIA Common lab., Rennes, France
2 INRIA Rennes-Bretagne Atlantique, France

Abstract Telecommunication networks are now an interconnection of competitive operators that need to cooperate to ensure end-to-end delivery of traffic. Inter-domain agreements have to be performed, and pricing is seen as a relevant way to reward intermediate domains for forwarding the traffic of others. In previous works, Vickrey–Clark–Groves (VCG) double-sided auctions have been applied because they provide proper incentives, lead to an efficient use of the network, and verify other relevant characteristics. However, it has been highlighted that the resource allocation schemes applying VCG auction are neither budget-balanced nor solvable in a decentralized way. In this paper, we apply combinatorial double-sided auction to allocate the bandwidth resources over nodes. While previous works were using a centralized algorithm, we use here a new pricing rule, leading to a new budget-balanced pricing scheme for which allocations and charges can be computed in a decentralized way. We also analyze the impact of this scheme on the game over declared costs of nodes.

Keywords  Resource allocation – Inter-domain – Network management – Game theory – Auctions

Estimation of cross-polarization due to rain over some stations in Nigeria

Joseph Sunday Ojo
Federal University of Technology, Akure, Nigeria

Abstract The statistical morphology of cross-polarization due to rain is of considerable interest to system designers in order to estimate accurately the signal total availability of time. In this paper, an attempt has been made to compute cross-polarization of millimeters waves in the Ku- and Ka-band frequencies range due to rain. ITU-R P.618-9 model has been used to predict cross-polarization discrimination (XPD) over three different elevation angles in Nigeria with modification using log-normal distributions of raindrop sizes at 20°C and assuming circular polarization for Earth–satellite propagation paths. The study includes a number of earth stations in Nigeria, namely Akure, Ikeja, Calabar, Minna, and Kano. Variations of co-polar attenuation with XPD as well as cumulative distribution of XPD have also been presented. The result of the estimation of XPD at various elevations angles and at the frequencies considered shows the dependence of XPD on frequency, co-polar attenuation, and rainfall rates. The orthogonal channels at the same frequency situated at the coastal region is prone to higher amount of unwanted signal mostly at the elevation angle of 23° (for communication links over the Indian Ocean) than at other elevation angles considered in this report.

Keywords  Rainfall rate – Cross-polarization discrimination – Lognormal distributions – Ku and Ka bands

When should I use network emulation?

Emmanuel Lochin1,2, Tanguy Pérennou1,2 and Laurent Dairaine2
1 CNRS; LAAS, Toulouse, France
2 Université de Toulouse, UPS, INSA, INP, ISAE; LAAS, Toulouse, France

Abstract The design and development of a complex system requires an adequate methodology and efficient instrumental support in order to early detect and correct anomalies in the functional and non-functional properties of the tested protocols. Among the various tools used to provide experimental support for such developments, network emulation relies on real-time production of impairments on real traffic according to a communication model, either realistically or not. This paper aims at simply presenting to newcomers in network emulation (students, engineers, etc.) basic principles and practices illustrated with a few commonly used tools. The motivation behind is to fill a gap in terms of introductory and pragmatic papers in this domain. The study particularly considers centralized approaches, allowing cheap and easy implementation in the context of research labs or industrial developments. In addition, an architectural model for emulation systems is proposed, defining three complementary levels, namely hardware, impairment, and model levels. With the help of this architectural framework, various existing tools are situated and described. Various approaches for modeling the emulation actions are studied, such as impairment-based scenarios and virtual architectures, real-time discrete simulation, and trace-based systems. Those modeling approaches are described and compared in terms of services, and we study their ability to respond to various designer needs to assess when emulation is needed.

Keywords  Experimentation – Emulation – Protocol – Internet

Analysis of three-dimensional turbo codes

Dhouha Kbaier Ben Ismail, Catherine Douillard and Sylvie Kerouédan
Institut Télécom, Télécom Bretagne, UMR CNRS 3192, Lab-STICC, Université Européenne de Bretagne, France

Our paper presents a detailed study of the three-dimensional turbo code (3D TC). This code which combines both parallel and serial concatenation is derived from the classical TC by concatenating a rate-1 post-encoder at its output. The 3D TC provides very low error rates for a wide range of block lengths and coding rates, at the expense of an increase in complexity and a loss in convergence. This paper deals with the performance improvement of the 3D TC. First, we optimize the distance spectrum of the 3D TC by means of the adoption of a non regular post-encoding pattern. This allows us to increase the minimum hamming distance (MHD) and thereby to improve the performance at very low error rates. Then, we propose a time varying construction of the post-encoded parity in order to reduce the observable loss of convergence at high error rates. Performance comparisons are made between the 3GPP2 standardized TC and the corresponding 3D code. The different improvement stages are illustrated with simulation results, asymptotical bounds, and EXIT charts.

Keywords  Turbo code – Iterative decoding – Three-dimensional turbo code – 3GPP2 code – Convergence threshold – Time varying trellis

A routing protocol using a reliable and high-throughput path metric for multi-hop multi-rate ad hoc networks

Hieu Cao Trong, Sungwon Lee and Choong Seon Hong
Kyung Hee University, Seoul, South Korea

Abstract In this paper, a high-throughput routing protocol for multi-rate ad hoc networks using lower layer information is proposed. By choosing the route with the minimum value of the proposed “Route Assessment Index” metric which has the form of entropy function, the selected route is ensured to have high throughput and link reliability among route candidates. Link bottleneck is avoided in the chosen route; hence, the packet drop rate due to buffer overflow is alleviated. Furthermore, an effective route discovery strategy is also introduced along with new routing metric. The correctness of the proposal is proven, and the simulation results show that our new metric provides an accurate and efficient method for evaluating and selecting the best route in multi-rate ad hoc networks.

Keywords  Multi-rate ad hoc networks – High throughput – Reliability – Routing metric – Cross layer

Beam reconfiguration of linear array of parallel dipole antennas through switching with real excitation voltage distribution

Banani Basu and G. K. Mahanti
National Institute of Technology, Durgapur, India

Abstract In this paper, authors propose a method based on the modified particle swarm optimization (PSO) for beam reconfiguration of linear array of mutually coupled parallel half-wavelength dipole antennas with real excitation voltage amplitude distribution. Two different beam pairs are generated, one pencil/pencil beam pair and another pencil/flat-top beam pair in the horizontal plane. One beam is changed to another through switching while sharing a common amplitude distribution. Two examples are presented, one without ground plane and another in presence of ground plane. Dipoles are connected to its feed network through a switch, so that it can be turned on or off, depending on the switch position. Beam reconfiguration is achieved by suitably turning the array elements on or off using same voltage excitation distribution. Modified PSO is used to compute the excitation voltages as well as the switching configuration for each pattern having a prefixed side lobe level. The current in the driven and parasitic elements is determined via induced EMF method considering the current distribution on each dipole to be sinusoidal. Proposed method efficiently synthesizes dual-beam switching the power pattern from pencil to pencil and pencil to flat-top having same or different side lobe levels using common excitation voltages. It calculates the maximum variation of the active impedance of driven elements and the power losses when the radiation patterns switch from one beam to another. The paper calculates the array directivity as the distances between antenna array and the ground pane varies. Three other state-of-the-art metaheuristics like differential evolution, gravitational search algorithm, artificial bee colony algorithm are also employed for achieving a comparative evaluation.

Modified particle swarm optimization – Switching – Beam reconfiguration – Linear array – Dipole antennas – Mutual coupling