TÉCNICAS DE CROSS-LAYER NA OPTIMIZAÇÃO DA INTEROPERABILIDADE EM SISTEMAS DE COMUNICAÇÕES MÓVEIS PÓS-3G

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Publications

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

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

HSDPA/WiFi RAT Selection Based on Load Suitability

Publication . Monteiro, Valdemar; Cabral, Orlando; Rodriguez, Jonathan; Velez, Fernando José; Gameiro, Atílio

Radio access technologies (RATs) selection algorithms have been studied in the literature and nowadays equipment with several RATs incorporated into it is already common. The major goal of this work is to measure the gain obtained by using WiFi as a backup network for HSDPA, allowing for preventing from quality of service (QoS) deterioration when in a low mobility scenario. Since IEEE 802.11e already supports QoS, it was the natural choice. The proposed RAT selection algorithm is based on the load of each system, and the results show a gain of 60% on supported network load with QoS over the HSDPA-alone system. As a consequence, when there is heavy load for the IEEE 802.11e network, acceptance of high priority services will affect the delay in low priority services, like FTP.

2008-06Conference object

Open access

Intra-operator spectrum sharing concepts for energy efficiency and throughput enhancement

Publication . Holland, Oliver; Attar, Alireza; Cabral, Orlando Manuel Brito; Velez, Fernando J.; Aghvami, A. Hamid

Cognitive radio and other dynamic spectrum sharing paradigms have enjoyed the limelight recently for their potential to realize a number of benefits for communications systems. The majority of investigated solutions thus far have looked at primary/secondary access and sharing of spectrum among different spectrum owners. In contrast, this paper investigates solutions for spectrum sharing among different bands owned by the same entity, such as a mobile operator, and demonstrates considerable potential for such solutions to improve power efficiency for the network and to increase throughput. The paper utilizes four means to achieve this potential: spectrum sharing through the opportunistic movement of users between bands allowing radio network equipment in other bands to be switched off when possible, spectrum sharing to opportunistically improve links’ propagation characteristics therefore reducing necessary transmission power, better interference management in spectrum sharing to reduce necessary transmission power, and the opportunistic aggregation of spectrum bands to increase achievable throughput. Power consumption reductions of over 50%, both in terms of mains power draw and in terms of necessary transmission power, are demonstrated. Moreover, throughput enhancements of up to 20% are achieved.

2010-11Conference object

Open access

Experimental System Level Platform for B3G Scenarios

Publication . Monteiro, Valdemar; Bastos, Joaquim; Cabral, Orlando Manuel Brito; Velez, Fernando J.; Rodriguez, Jonathan

This paper provides a complete specification of the packet based cellular wireless system level simulator that addresses a beyond 3G scenario involving heterogeneous wireless systems interconnected via an IP backbone network. Important aspects as the Link layer design (including the MAC layer) are specified, as well as the C++ object oriented simulation architecture. Since the IP level and the physical layer aspects should be avoided, interfaces representing these layers are proposed for different type of radio access systems. The concept is showcased by a multi-RAT system composed of HSDPA and a Wi-Fi system using load balancing techniques.

2010-05Conference object

Open access