No. 1 (2008)
Published:
2008-03-30
ARTICLES FROM THIS ISSUE
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Making ad hoc networking a reality: problems and solutions
Abstract
Despite the fact that many electronic evices are equipped with wireless interfaces and numerous publications on wireless ad hoc and mesh networking exist, these networks are seldom used in everyday life. A possible explanation is the fact that only few of the numerous theoretically promising proposals lead to practical solutions on real systems. Currently, wireless network design is mostly approached from a purely theoretical angle. In this paper, common theoretical assumptions are challenged and disproven, and key problems that are faced when putting theory to practice are determined by experiment. We show how these problems can be mitigated, and motivate why a heterogeneous hierarchical wireless mesh architecture, and a multidisciplinary research approach can help in making wireless ad hoc networking a reality.
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Practical analysis of IEEE 802.11b/g cards in multirate ad hoc mode
Abstract
In multirate ad hoc networks, mobile stations usually adapt their transmission rates to the channel conditions. This paper investigates the behavior of IEEE 802.11b/g cards in a multirate ad hoc environment. The theoretical upper bound estimation of the throughput in multirate ad hoc networks is derived. The measurement scenarios and obtained results are presented. For result validation the theoretical and experimental values are compared. The achieved results, presented in the form of figures, show that cards manufactured by independent vendors perform differently. Therefore, choosing the optimum configuration, according to the user’s requirements, is possible
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A hybrid-mesh solution for coverage issues in WiMAX metropolitan area networks
Abstract
The new WiMAX technology offers several advantages over the currently available (GSMor UMTS-based) solutions. It is a cost effective, evolving, and robust technology providing quality of service guarantees, high reliability, wide cov- erage and non-line-of-sight (NLOS) transmission capabilities. All these features make it particularly suitable for densely populated urban environments. In this paper we discuss the design and implementation difficulties concerning network coverage discovered in a test-bed implementation of WiMAX. We point out the presence of unexpected “white spots” in the coverage, which are not inherently characteristic of the WiMAX concept. As a possible remedy to this significant drawback of the otherwise very promising technology, we consider reconfigurable mesh organization of WiMAX base stations. We also suggest directions for further development of this kind of network operation, partly based on our practical experience. Despite the clear advantages of the mesh mode in WiMAX networks, its development is currently at an early stage, due to the high complexity of the necessary mechanisms. In this situation, we propose an original, much simpler solution: the so-called support-mesh mode.
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On a practical approach to low-cost ad hoc wireless networking
Abstract
Although simple wireless communication involving nodes built of microcontrollers and radio devices from the low end of the price spectrum is quite popular these days, one seldom hears about serious wireless networks built from such devices. Most of the commercially available nodes for ad hoc networking (somewhat inappropriately called "motes") are in fact quite serious computers with megabytes of RAM and rather extravagant resource demands. We show how one can build practical ad hoc networks using the smallest and cheapest devices vailable today. In our networks, such devices are capable of sustaining swarm-intelligent sophisticated routing while offering enough processing power to cater to complex applications involving distributed sensing and monitoring.
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A simple vehicle classification framework for wireless audio-sensor networks
Abstract
Vehicle tracking is one of the important applications of wireless sensor networks. We consider an aspect of tracking: the classification of targets based on the acoustic signals produced by vehicles. In this paper, we present a naıve classifier and simple distributed schemes for vehicle classification based on the features extracted from the acoustic signals. We demonstrate a novel way of using Aura matrices to create a new feature derived from the power spectral density (PSD) of a signal, which performs at par with other existing features. To benefit from the distributed environment of the sensor networks we also propose efficient dynamic acoustic features that are low on dimension, yet effective for classification. An experimental study has been conducted using real acoustic signals of different vehicles in an urban setting. Our proposed schemes using a na¨ıve classifier achieved highly accurate results in classifying different vehicles into two classes. Communication and computational costs were also computed to capture their trade-off with the classification quality.
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Multi-threshold signature
Abstract
The work presents a new signature scheme, called the multi-threshold signature, which generalizes the concept of multisignature and threshold signature. This scheme protects the anonymity of signers in a way the group signature does – in exceptional circumstances the identities of signers may be revealed. Due to the new party – completer, in our scheme the threshold size may vary together with the message to be signed. The presented scheme is based on the RSA signature standard, however other signature standards might be applied to it as well.
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Temperature dependence of polarization mode dispersion in tight-buffered optical fibers
Abstract
Experiments and theoretical analysis of influence of temperature on polarization mode dispersion (PMD) in single mode optical fibers and cables are presented. Forces generated by contracting buffer create optical birefringence and increase fiber PMD at low temperatures. Single mode fiber (SMF) in 0.9 mm polymeric tight-buffer can exhibit an extra component of PMD exceeding 0.3 ps/√km in such conditions. On the other hand, tight-buffered spun nonzero dispersion-shifted fibers (NZDSF) and optical units with stranded single mode fibers have showed good stability of PMD over wide range of temperatures. This is due to presence of circular strain in the core, blocking accumulation of mechanically induced birefringence.
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Rain precipitation in terrestrial and satellite radio links
Abstract
This paper covers unavailability of terrestrial and satellite line-of-sight radio links due to rain. To evaluate the rain effects over communication system, it is essential to know the temporal and spatial evolution of rainfall rate. Longterm 1-min average rain-rate characteristics necessary for the design of microwave radio links are determined for central Poland. 1-min rain rate distributions are presented. It also describes comparison results of predicted attenuation obtained from ITU-R formula and empirical data at frequency bands 11 GHz and 18 GHz and satellite 12 GHz. The National Institute of Telecommunications stores 11-year long rain intensity characteristics (1985–1996), based on data derived on 15.4 km long experimental path. In this paper chosen experimental data are presented.
