1,721,031 research outputs found
Throughput versus fairness tradeoff analysis
No full textOptimal resource allocation is an outstanding issue in wireless communication systems. In this work we focus on the ever challenging optimization of the tradeoff between throughput and fairness. Specifically, we propose a novel framework to analytically derive the maximum average throughput versus fairness under the assumptions that the throughput of each user i) increases if more resources are allocated to him and ii) depends on how many resources and not which resources are allocated. We achieve a general formulation of the tradeoff optimization problem and we also derive and validate a closed form solution in those scenarios where throughput linearly depends on resources, which cover several realistic cases. Besides these valuable results, the framework also lays solid basis toward a more general solution
On the exploitation of OFDMA properties for an efficient alert message flooding in VANETs
No full textVehicular ad hoc networks (VANETs) drive new challenging research issues at different layers of the protocol pillar, from physical to application. Focusing on the medium access layer, one of the most promising and not yet fully explored option is the adoption of orthogonal frequency division multiple access (OFDMA). Besides guaranteeing high spectral efficiency and effective resource allocation, it relies at the physical layer on orthogonal frequency division multiplexing, which allows repetitions of the same signals to be opportunistically combined at the receiver even if they are not perfectly synchronized. Exploiting this property, here we suggest and discuss the use of OFDMA for alert message flooding in VANETs to increase reliability and resource usage efficiency. The achievable benefit and the potential drawback (in terms of high delivery delay) are here assessed through a simple yet realistic model that allows to compare, in highway scenarios, OFDMA with carrier sensing multiple access/collision avoidance, currently adopted by IEEE 802.11p for distributed communications in high mobility scenarios
Mobile WiMAX Performance Investigation
No full textAlthough the Mobile-WiMAX technology is being deployed in the United States, Europe, Japan, Korea, Taiwan and in the Mideast, there are still ongoing discussions about the potential of this technology. What is really remarkable, in fact, with regard to the Mobile-WiMAX profile, is the high number of degrees of freedom that are left to manufacturers. The final decision on a lot of very basic and crucial aspects, such as, just to cite few of them, the bandwidth, the frame duration, the duplexing scheme and the up/downlink traffic asymmetry, are left to implementers. It follows that the performance of this technology is not clear yet, even to network operators.
This consideration motivated our work, which is focused on the derivation of an analytical framework that, starting from system parameters and implementation choices, allows to
evaluate the performance level provided by this technology, carefully taking all aspects of IEEE802.16e into account. In particular, the analysis starts from the choices to be made at the
physical layer, among those admitted by the specification, and "goes up" through the protocol pillar to finally express the application layer throughput and the number of supported
voice over IP (VoIP) users, carefully considering "along the way" all characteristics of the the medium access control (MAC) layer, the resource allocation strategies, the overhead introduced,
the inherent inefficiencies, etc
On the use of OFDMA for next generation vehicular ad hoc networks
No full textVehicular ad hoc networks (VANETs) based on
IEEE 802.11p are moving new safety and traffic applications
beyond the present limitations given by infrastructures. However,
due to the high variability in time and position of nodes,
the medium access control layer of IEEE 802.11p, which is
based on carrier sensing multiple access with collision avoidance
(CSMA/CA), could lead to severe performance degradation in
terms of delivery delay and delivery ratio as the node density
increases. Because of its higher efficiency, we propose the use of
orthogonal frequency division multiple access (OFDMA) as access
technique in VANETs, discussing and evaluating i) its feasibility,
ii) the challenges posed by the distributed allocation of resources,
and iii) its performance in terms of resource allocation efficiency
(specifically, delivery rate and delivery delay) when compared
to CSMA/CA. Results, obtained by means of simulations that
jointly take into account realistic road maps, vehicular traffic,
and the whole network architecture from the application down
to the physical layer, show that OFDMA allows up to four times
higher delivery rate and that it also guarantees lower delivery
delay in heavy loaded network conditions
Optimal transmission policies for energy harvesting nodes with partial information of energy arrivals
No full textAbstract—When energy is harnessed by wireless nodes from renewable
sources, its availability becomes uncertain and its use for
communications must be carefully designed. While the optimal
power allocation has been derived in previous works when energy
availability is fully (a priori) known, practical algorithms are
needed when only causal and statistical information is available.
In this paper, we study the optimal transmission policy when
only the statistical distribution of the energy arrival intervals is
known and no information is available on the amount of energy
that will be harnessed. We firstly obtain an exact solution for
the case of a step-wise transmission power profile. This result is
then extended to the time-continuous case. Within energy arrival
intervals, the obtained power profile is shown to be non increasing
as a function of time and non decreasing as a function of the
residual energy. Numerical results are finally provided focusing
on an exponentially distributed energy arrival process as a case
study
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
Optimizations for Hardware-in-the-Loop-Based V2X Validation Platforms
No full textConnectivity and automation are increasingly getting importance in the automotive industry, which is observing a radical change from vehicles driven by humans to fully automated and remotely controlled ones. The test and validation of all the related devices and applications is thus becoming a crucial aspect; this is raising the interest on hardware-in-the-loop (HiL) platforms which reduce the need for complicated field trials, thus limiting the costs and delay added to the process. With reference to the test and validation of vehicle-to-everything (V2X) communications aspects, and assuming either sidelink LTE/5G-V2X or IEEE 802.11p/bd technologies, in this work we focus on the real-time HiL simulation of the information exchanged by one vehicle under test and the surrounding, simulated, objects. Such exchange must be reproduced in a time-efficient manner, with elaborations done fast enough to allow testing the applications in real-time. More precisely, we discuss the simulation of non-ideal positioning and channel propagation taking into account current impairments. We also provide details on optimization solutions that allowed us to trade-off minor loss in accuracy with a significant reduction of the computation time burden, reaching up to more than one order of magnitude speed increase in our experiments
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