1,721,031 research outputs found
OUTAGE PROBABILITY IN FDMA/TDMA MOBILE COMMUNICATION NETWORKS
No full textOne of the most crucial problems to solve in the field of mobile communication networks is the evaluation for a generic link of the network of the outage probability due to the random characteristic of the transmission system, essentially determined by anomalous propagation conditions, cochannel interference and user mobility. The exact analytical solution to this problem is very burdensome, regardless to the system implementation technique considered. In this paper the effects of cochannel interference, nonselective fading and user mobility in FDMA/TDMA mobile radio networks are investigated, and an extremely simple approximated methodology is presented for the analytical evaluation of the outage probability and of the frequency reuse distance. It is worth noting that the proposed method allows to consider a general statistical description for the nonselective propagation media of the radio network. Here we successfully apply it the path loss, fading and shadowing scenario which are typical of cellular and microcellular structures
OUTAGE PROBABILITY FOR CELLULAR MOBILE RADIO SYSTEMS: SIMPLIFIED ANALYTICAL EVALUATION AND SIMULATION RESULTS
No full textA simulation program has been carried out to further check the simplified method proposed by Immovilli and Merani for the analytical evaluation of outage probability in cellular mobile radio systems, due to cochannel interference and random propagation phenomena, nonselective in type. The results of the two different procedures show an excellent agreement
End-to-end TCP Enhancements Performance on Satellite Links
No full textAlthough TCP has proved very effective and robust for
many years, its performance on emerging heterogeneous
networks is challenged by the impairments originated by the
presence of radio links. In particular, satellite communications
are affected by long RTTs and possibly also by random segment
losses, which can severely affect end-to-end performance. To cope
with these problems, several TCP enhancements have been
presented in the literature. The paper aim is to investigate the
effectiveness of such modifications, when applied to TCP satellite
connections. In particular, the analysis focuses on some emerging
proposals, namely TCP Hybla, developed by the authors, and
TCP Westwood, examined here in three variants. They are
compared with three well established TCP variants, such as
NewReno, SACK and Vegas, taking into account both a pure
satellite environment and more challenging, but also perhaps
closer to reality, heterogeneous network. Performance is assessed
by means of ns-2 simulations considering goodput, fairness and
friendliness as performance metrics. Results show that large
performance improvements may be achieved by some of the
considered TCP enhancements, without infringing the end-to-end
semantics of this protocol
DTNperf_3: A further enhanced tool for Delay-/Disruption- Tolerant Networking Performance evaluation
No full textDelay-/Disruption- Tolerant Networking (DTN) was first conceived to cope with the impairments of Inter-Planetary Internet. Then its scope was enlarged to cover all “challenged networks”, where long delays, disruption, link intermittency and other challenges prevent, or make difficult, the use of ordinary Internet architecture. To assess DTN performance in such heterogeneous scenarios as space communications (including both satellite and deep space) and wireless sensor networks, it is essential to develop suitable evaluation tools, with highly flexible use. In this paper we present the third major release of DTNperf, a client-server evaluation tool designed to assess goodput and to provide logs in DTN Bundle Protocol (BP) architectures. It has been greatly extended in many respects, including full support of both DTN2 and ION (the BP reference implementation and that developed by NASA JPL, respectively). The aim of the paper is to present both new and enhanced features and a variety of application examples, mainly focused on satellite and space communications, in order to promote its use within the DTN community. DTNperf_3 is to be included in DTN2, as were previous versions, and for the first time also in ION
Satellite communications: From PEPs to DTN
Full text linkDelay-/Disruption-Tolerant Networking represents an innovative way to cope with satellite communications impairments. In this view, the paper presents an in-depth analysis of implications of a DTN approach to satellite communications, focusing on these fundamental aspects: network architecture, security, and Quality of Service (QoS). For each topic, commonalities and differences between DTN and Performance Enhancing Proxies (PEPs) are highlighted, to show that the DTN architecture can be seen as a promising evolution of PEPs, at present the most widely adopted architecture. The analysis shows that DTN can effectively improve PEPs functionalities in the presence of intermittent and disruptive channels and/or a high level of network heterogeneity. In particular, DTN offers the possibility to operate with intermittent channels, a better resilience to channel disruptions, the possibility to implement both end-to-end and hop-by-hop security, and a greater flexibility in the use of advanced QoS techniques
Impact of fast fading compensations on mobile radio system performance
No full textThis paper explores what benefits can result from the compensation of both log-normal shadowing and Rayleigh/Rice-fading fluctuations in a mobile radio environment. The focus is on those power-control policies that exclusively make use of local power-level measurements in order to improve the performance, measured in terms of signal-to-cochannel interference ratio, of time-division multiple-access cellular radio systems; the aim is in fact to demonstrate under what circumstances the power compensation can be advantageously exploited. The corresponding analysis accounts for the errors due to the delay constraints that time-division and transmission techniques such as interleaving inevitably force onto the control loops. The numerical results quantitatively outline the maximum benefits on system performance that derive from the introduction of fast fading compensation for the class of power-control policies investigated in this paper. The remarkable influence of delay errors on the effectiveness of the fast fading control procedures are clearly revealed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
DTN meets smartphones: future prospects and tests
No full textAlthough first conceived for the Interplanetary Internet, DTN (Delay-/Disruption-Tolerant Networking) architecture has successively enlarged its application scope to embrace all “challenged networks”, i.e. networks where the TCP design key assumptions of short RTT, no disruptions, and continuous end-to-end path availability are challenged. The distinctive features of DTN architecture seem ideal for the connectivity problems of modern smartphones. These are both PCs and cell phones and are characterized by a wide range of different communications technologies, including Bluetooth, WiFi, and advanced 3G radio interfaces, like UMTS HSPA (High-Speed Packet Access). The aim of this paper is to show that it is both feasible and useful to adopt DTN architecture on these advanced devices, in addition to the usual TCP/IP protocol stack. To this end, a series of tests is presented and discussed in the paper, considering various communication interfaces, 3G in particular. Tests were greatly facilitated by the introduction onto the market of some smartphones running Linux based operating systems, like Maemo, which allowed the authors the direct use of “official” DTN code (i.e. the DTN2 reference implementation and the DTNperf_2 evaluation tool)
DTNperf_2: a Performance Evaluation tool for Delay/Disruption Tolerant Networking
No full textDelay/Disruption Tolerant Networking (DTN) has recently been proposed as a very effective solution to cope with the problems posed by challenged networks (long delays, disruptions, absence of end-to-end connectivity, etc.). In order to assess DTN performance in such scenarios, it is essential to be able to rely on specific evaluation tools. In this paper we present DTNperf_2, which is a client-server evaluation tool designed to assess goodput and to provide logs in DTN bundle layer architectures. The aim is to facilitate the adoption of this tool by the DTN research community. DTNperf_2 features, design and usage are discussed in detail. Moreover, an example of use is given, to demonstrate its capabilities. DTNperf_2 is included in the official DTN suite released by DTNRG
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