17 research outputs found
A Mathematical Model for Evaluating the Performance of Multicast Systems
© 2008 IEEE. Reprinted, with permission, from Syed S. Rizvi, Aasia Riasat, and Khaled M. Elleith, "A Mathematical Model
for Evaluating the Performance of Multicast Systems," The 1st IEEE
International Workshop on IP Multimedia Communications (IPMC 2008) August 4 - 7, 2008, St. Thomas U.S. Virgin IslandsThe Internet is experiencing the demand of high-speed real-time applications, such as live streaming multimedia, videoconferencing, and multiparty games. IP multicast is an efficient transmission technique to support these applications. However, there are several architectural issues in this technique that hinder the development and the deployment of IP multicast such as a lack of an efficient multicast address allocation scheme. On the other hand, End System Multicasting (ESM) is a very promising application-layer scheme where all the multicast functionality is shifted to the end-users. Supporting high-speed real-time applications always demand a sound understanding of these schemes and the factors that might affect the end-user requirements. In this paper we attempt to propose both analytical and the mathematical models for characterizing the performance of IP multicast and ESM. Our proposed mathematical model can be used to design and implement a more efficient and robust ESM model for the future networks
Cell identification based on received signal strength fingerprints: concept and application towards energy saving in cellular networks
The increasing deployment of small cells aimed at off-loading data traffic from macrocells in heterogeneous networks has resulted in a drastic increase in energy consumption in cellular networks. Energy consumption can be optimized in a selforganized way by adapting the number of active cells in response to the current traffic demand. In this paper we concentrate on the complex problem of how to identify small cells to be reactivated in situations where multiple cells are concurrently inactive. Solely based on the received signal strength, we present cell-specific patterns for the generation of unique cell fingerprints. The cell fingerprints of the deactivated cells are matched with measurements from a high data rate demanding mobile device to identify the most appropriate candidate. Our scheme results in a matching success rate of up to 100% to identify the best cell depending on the number of cells to be activated
A random access MAC protocol for MPR satellite networks
Dissertação apresentada para obtenção do Grau de Mestre em Engenharia Electrotécnica e de Computadores, pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaRandom access approaches for Low Earth Orbit (LEO) satellite networks are usually incompatible
with the Quality of Service (QoS) requirements of multimedia tra c, especially when hand-held devices must operate with very low power.
Cross-Layered optimization architectures, combined with Multipacket Reception (MPR)schemes are a good choice to enhance the overall performance of a wireless system. Hybrid
Network-assisted Diversity Multiple Access (H-NDMA) protocol, exhibits high energy e ciency, with MPR capability, but its use with satellites is limited by the high round trip time. This protocol was adapted to satellites, in Satellite-NDMA, but it required a pre-reservation mechanism that introduces a signi cant delay.
This dissertation proposes a random access protocol that uses H-NDMA, for Low Earth Orbit (LEO) satellite networks, named Satellite Random-NDMA (SR-NDMA). The protocol addresses the problem inherent to satellite networks (large round trip time and signi cant energy consumption) de ning a hybrid approach with an initial random access plus possible additional scheduled retransmissions. An MPR receiver combines the multiple copies received, gradually reducing the error rate. Analytical performance models are proposed for the throughput, delay, jitter and energy e ciency considering nite queues at the terminals. It is also addressed the energy e ciency optimization, where the system
parameters are calculated to guarantee the QoS requirements.
The proposed system's performance is evaluated for a Single-Carrier with Frequency Domain Equalization (SC-FDE) receiver. Results show that the proposed system is energy e cient and can provide enough QoS to support services such as video telephony
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Crab and cockle shells as heterogeneous catalysts in the production of biodiesel
In the present study, the waste crab and cockle shells were utilized as source of calcium oxide to transesterify palm olein into methyl esters (biodiesel). Characterization results revealed that the main component of the shells are calcium carbonate which transformed into calcium oxide
upon activated above 700 °C for 2 h. Parametric studies have been investigated and optimal conditions were found to be catalyst amount, 5 wt.% and methanol/oil mass ratio, 0.5:1. The waste catalysts perform equally well as laboratory CaO, thus creating another low-cost catalyst source for producing biodiesel. Reusability results confirmed that the prepared catalyst is able to be reemployed up to five times. Statistical analysis has been
performed using a Central Composite Design to evaluate the contribution and performance of the
parameters on biodiesel purity