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Publications

Publications by Nuno Teixeira Almeida

2004

High-speed wireless LANs: Modeling and simulation of enhanced ARQ strategies

Authors
Almeida, NT;

Publication
8TH WORLD MULTI-CONFERENCE ON SYSTEMICS, CYBERNETICS AND INFORMATICS, VOL III, PROCEEDINGS: COMMUNICATION AND NETWORK SYSTEMS, TECHNOLOGIES AND APPLICATIONS

Abstract
This paper focuses on improved error control schemes for highspeed wireless digital communications. The main objective is a better quality support for real-time services, such as video, when using wireless mobile digital networks. In view of that, and besides the schemes already standardized, a novel error control mechanism is proposed. This new mechanism relies mainly in the use of Hybrid Automatic Repeat reQuest (HARQ) error control schemes and differentiated error robustness transmission modes. In this sense, when implementing this new technique, some of the capabilities offered by modem Wireless Local Area Networks (WLANs) are significantly better utilized. To make the performance analysis of the proposed error control mechanism, and corresponding comparison with existing systems, it was developed a system simulation environment, together with other computational tools. Analysis for diverse radio channel conditions, from AWGN modeling to Gilbert-Elliot modeling, has been done and some examples are subsequently presented. The simulation results show that this new strategy greatly improves the performance of real-time services, fulfilling the requirement of limited delays and enabling higher data rates.

1992

END-TO-END SYNCHRONIZATION IN PACKET-SWITCHED NETWORKS

Authors
ALMEIDA, N; CABRAL, J; ALVES, A;

Publication
LECTURE NOTES IN COMPUTER SCIENCE

Abstract
The provision of real time services through a Packet Switched Network, requires the adoption of end-to-end synchronization methods. Several of these methods, are compared and a specific hardware solution is discussed. Results obtained through a specially designed Simulation Programme are included, for several network time delay jitter distributions and synchronization methods. These results are used to evaluate systems and design parameters.

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