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Implementation of IEEE 802.11e block acknowledgement policies based on the buffer size

Publication . Cabral, Orlando; Segarra, Alberto; Velez, Fernando J.

Optimization of IEEE 802.11e MAC protocol performance is done by modifying several parameters left open in the standard, like buffer size and acknowledgement policies. By using the developed event-driven simulator, results were extracted with single and multi-service. With only a single service, higher values for the goodput are obtained for video and background (BK) traffics in comparison with the voice (VO) application. Besides, the number of supported user is higher for voice. With mixtures of traffic, when the number of station is small the goodput is lower for VO. However, for higher number of station, the lowest values for the goodput occur for background traffic. By using the Block Acknowledgement (ACK) procedure, for video and BK traffics, the capacity is improved when the number of station is equal or higher than 16 and 12, respectively. From a detailed analysis of the video application, a reduction of more than 40% was achieved in the delay. However, a clear trend is not identified for the optimum block size.

2008-06Conference object

Open access

Simulation of IEEE 802.11e in the context of interoperability

Publication . Cabral, Orlando; Segarra, Alberto; Velez, Fernando José

This work provides the specification of a MAC layer simulator that evaluates the service quality in WiFi, and presents initial results as a stand-alone simulator. The simulator will account for inter-working with WiMAX and HSDPA in the context of the IT-MOTION tool. Higher throughputs are found for the FTP service and for the video service, mainly because the frames transmitted in these services are longer than the ones for the voice application. However, the number of supported users is higher for voice. This simulator will allow for tuning-up several parameters like the ones related to how to use BlockACK, normal ACK, and NO ACK policies.

2007-07Conference object

Open access

Optimization of Multi-Service IEEE 802.11e Block Acknowledgement

Publication . Cabral, Orlando; Velez, Fernando José; Mihovska, Albena Dimitrova; Prasad, Neeli

Optimization of IEEE 802.11e MAC protocol performance is addressed by modifying several parameters left open in the standard, like block size and acknowledgement policies in order to improve the channel efficiency. The use of small block sizes leads to a high overhead caused by the negotiation on the other hand, the use of large block sizes causes long delays, which can affect negatively real-time applications (or delay sensitive applications). An event driven simulator was developed, and results with a single service and several services running simultaneously were extracted. By using the Block Acknowledgement (BA) procedure, for video and background traffics in a single service situation, the capacity was improved in the case when the number of stations is equal or higher than 16 and 12, respectively. However, for lower values of the number of stations, the use of BA leads to a slightly worst system performance. In a scenario with mixture of services the most advised block size is 12 (less delay in a highly loaded scenario). The number of supported user (total) increases from 30 to 35.

2009-01Conference object

Open access

Cross-layer multi-hop simulator for ad-hoc IEEE 802.11e

Publication . Ferro, João Miguel; Velez, Fernando José

The purpose of this paper is to present a custom-made cross-layer network simulator for wireless IEEE 802.11e in a multihop environment. A previous work of our research team created a simulator just for the physical plus MAC layers, which in this work was adapted to model the transmission of a packet from a source to a destination using intermediate nodes. Some initial tests were performed using a simple routing algorithm, and the results obtained from these tests indicate that the system is capable of deliver the packets regardless of the source/destination, and successfully calculates several metrics such as end-to-end delay and number of packets lost.

2008-07Conference object

Open access

Hybrid WiMAX and Wi-Fi networks for the support of b-Learning and Telemedicine

Publication . Costa, Rui; Velez, Fernando José; Robalo, Daniel Luís Silveira; Marques, Marco; Comissário, Cláudio; Riscado, José; Cavaleiro, Victor; Sebastião, Pedro; Rodrigues, António

his paper addresses the deployment of hybrid WiMAX and Wi-Fi networks for the support of always best connected telemedicine and health sciences education applications. The available services include a LMS (Learning Management System) and several structured functionalities for b-Learning. For the support of these services, fixed and wireless LANs have been deployed, as well as an experimental point-to-multipoint IEEE 802.16-2004 network covering part of the city of Covilhã. The FCS (Health Sciences Faculty) Campus as well as the tutorial rooms of the Faculty spread at the different Hospitals of the region of Beira Interior, Portugal, are benefiting from WLAN coverage, whose backhaul is supported by WiMAX point-to-point links with relays. Field trials results were compared with the ones arising from the WiMAX radio links design, and very similar results were achieved. Service quality was guaranteed by adjusting QoS parameters.

2009-05Conference object

Open access