Browsing by Author "Cabral, Orlando Manuel Brito"
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- Cost/Revenue Optimisation of Multi-Service Cellular Planning for City Centre E-UMTSPublication . Velez, Fernando J.; Anastácio, Nuno; Merca, Francisco; Cabral, Orlando Manuel BritoAn overview of All-IP Enhanced Universal Mobile Telecommunication System, E-UMTS, service needs in the business city centre, BCC, scenario is first presented. Then, E-UMTS traffic generation and activity models are described and characterised. System level simulations are carried out and the enhanced performance is demonstrated based in a single quality parameter, which simultaneously accounts for call blocking and handover failure probabilities. End-to-end delays do not present a limitation. By considering a grade of service of 1% for the quality parameter, and different hypothesis for costs and prices, an optimum coverage distance is obtained around ~200-425 m, which maximises the supported throughput per km2. However, results for the profit in percentage indicates that coverage distances in the range 395-425 m should be used in BCC.
- A Cross-Layer Multi-Hop Simulator for IEEE 802.11ePublication . Ferro, João Miguel; Cabral, Orlando Manuel Brito; Velez, Fernando J.In this work we simulate the ad hoc mode of IEEE 802.11e for routing optimisation. We simulate the behaviour of routing algorithms at the network layer by using a custom-made cross-layer network simulator developed by our team, which simultaneously considers the physical and Medium Access Control (MAC) layers. Although the simulator also supports the infrastructure mode, in this paper we focus on the ad hoc feature which was introduced by the authors.We opted for the simulator approach over the theoretical analysis, butwe also present amathematical model for IEEE 802.11 ad hoc networks. Some initial tests were performed by using a simple routing algorithm (to evaluate the behaviour of the system in terms of selection of the path between a source and a destination, and the correctness of the calculated metrics,which include end-to-end delay, packets lost, packets delivered), but more advanced cross-layer design solutions were also tested. When information from the physical and MAC layers is used as an input to the routing algorithm, improvements are achieved in the performance of the network. Several functions were compared and the algorithm that privileges shorter links accounting with the metric “collision rate” achieves the best results. When compared with a standard routing solution, this cross-layer approach allows to increase the number of packets delivered, while not significantly affecting the end-to-end delay of the packets.
- Enhanced UMTS Cellular Planning for Multiple Traffic Classes in Offices ScenariosPublication . Cabral, Orlando Manuel Brito; Velez, Fernando J.; Hadjipollas, George; Stylianou, Marinos; Antoniou, Josephine; Vassiliou, Vasilis; Pitsillides, AndreasIt is shown that enhanced UMTS is an affordable solution for providing the required network quality and to reduce infrastructure investments in offices scenarios. System capacity results are obtained by using a system level simulator which considers traffic characterisation parameters and services usage in detail, among other. Results for the most profitable cell radius are obtained via an optimisation procedure based in economic aspects. A higher number of pico cells (with a smaller radius, around 30-32 m) can be installed in the future, when costs of deploying and maintaining the network decreases, allowing for supporting higher system capacity, and reducing prices. Our approach is based in a detailed services analysis, which represents a worst case situation relatively to the total services approach, because the later does not discriminate results for the different traffic classes. The impact of call blocking, handover failure, end-to-end delay, and delay variation are taken into account.
- Enhanced UMTS Cost/Revenue Optimisation in Offices ScenariosPublication . Cabral, Orlando Manuel Brito; Velez, Fernando José; Hadjipollas, George; Stylianou, Marinos; Antoniou, Josephine; Vassiliou, Vasilis; Pitsillides, AndreasIn this paper Enhanced UMTS offices scenarios and classes of services up to wideband are taken into account. A model is proposed for optimising Enhanced UMTS based in costs and revenues. A system level simulator is used to obtain the blocking probability, and other QoS measures, e.g., handover failure probability and delay. Using these results, one obtains the system capacity, i.e., the supported fraction of active users and throughput for a given grade of service. The profit (in percentage) was obtained, and the optimum (most profitable) cell radius was found. A higher number of pico-cells (with a cell radius around 34 m) will be a profitable solution for the optimisation of network planning. This will also allow for increasing system capacity and reducing prices.
- Enhanced UMTS Simulation-based Cellular Planning in Urban ScenariosPublication . Cabral, Orlando Manuel Brito; Velez, Fernando José; Franco, Cátia; Rei, RicardoAspects of cellular planning for E-UMTS (Enhanced UMTS) are addressed, and results for system capacity are obtained, as a function of the coverage distance. E-UMTS traffic generation and activity models are described and characterised, based on population and service penetration values. An urban scenario was defined with a selection of relevant multi-rate bursty applications. By using a System Level Simulator results were obtained for the end-to-end delay, and for blocking and handover failure probabilities. By using these results, models for the supported fraction of active users and throughput were obtained, as a function of the cell coverage distance. When the coverage distance decreases from 600 to ~200 m, the supported throughput per km2 increases from ~1Mb/s to ~5 Mb/s. By using trisectorial antennas with one amplifier a maximum throughput per BS of 600kb/s was obtained.
- Enhanced UMTS Simulation-based Planning in Office ScenariosPublication . Cabral, Orlando Manuel Brito; Velez, Fernando José; Hadjipollas, George; Stylianou, Marinos; Antoniou, Josephina; Vassiliou, Vasos; Pitsillides, AndreasEnhanced UMTS traffic characterisation parameters have been addressed for the offices scenario. By using a system level simulator, results concerning QoS measures as packet delay, blocking and handover failure probabilities have been obtained. If the cell radius decreases and the number of BSs increases the blocking probability decreases with a linear trend. One concludes that the supported traffic and the corresponding throughput significantly increase when the cell radius decreases. However, increasing system capacity by decreasing the cell radius causes an increase in the intensity of handovers and a decrease in the throughput per BS. Hence, optimum values for the coverage distance will correspond to higher cell radius. Delay and delay variation are not a limitation.
- Event-Driven Simulation for IEEE 802.11e OptimizationPublication . Cabral, Orlando Manuel Brito; Segarra, Alberto; Velez, Fernando J.This work provides the specification of a PHY and MAC layers simulator that allows to evaluate the IEEE 802.11e service quality. A detailed state transition diagram is presented along with a description of the related attributes and methods, an identification of the associated events and input variables, and a description of functions for events. For validation purposes, results of the goodput as a function of the signal to interference noise ratio were obtained with an error margin lower than 10%. Higher values are found for the goodput for background and video services, mainly because the frames transmitted in these services are longer than the voice application ones. 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.
- Experimental System Level Platform for B3G ScenariosPublication . Monteiro, Valdemar; Bastos, Joaquim; Cabral, Orlando Manuel Brito; Velez, Fernando J.; Rodriguez, JonathanThis 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.
- Highlights from the Workshop Pervasive Broadband Wireless Access: Toward Long-Term EvolutionPublication . Velez, Fernando J.; Cabral, Orlando Manuel Brito; Monteiro, Valdemar; Rodriguez, JonathanThe Final Workshop of the CROSSNET (Cross-Layer Design and Network Planning for B3G Systems, http://www.e-projects.ubi.pt/crossnet/) project took place on February 19, 2008, at Instituto de Telecomunicações, Portugal. There were 133 participants, 31 percent from academia, 22 percent from R&D laboratories, 15 percent from telecommunication services and maintenance, 11 percent from manufacturers, 11 percent from regulators, 7 percent from operators, and 3 percent from public bodies and safety ser- vices. From the feedback received from participants, the adhesion to the event was justified by their need to access discussion fora on technology trends and challenges in the telecommunications sector, and research on deployment strategies for pervasive broadband wireless access was faced as an endeavor. The keynote speakers were Prof. Elvino de Sousa, University of Toronto; Dr. Tom Rondeau, Trinity College Dublin; Prof. Loutfi Nuaymi, Telecom Bretagne; and Prof. Javier Gozalvez, Uwicore, University Miguel Hernandez, Spain, covering the topics of 4G visions, broadband wireless access, cognitive radio, and dynamic spectrum access. Presentations also covered opportunities, challenges, and visions for long-term evolution, vehicular communications, and future spectrum management. One of the proposals is to deploy base stations (or access points) organically building autonomous infrastructure wireless networks. The Workshop was sponsored by Ordem dos Engenheiros (Colégio de Engenharia Electrotécnica and Especialização de Telecomunicações), IEEE (Portugal Section and VTS Portugal Chapter), Academia de Ciências — Instituto de Altos Estudos, Academia de Engenharia, Advanced Resources, Alcatel-Lucent, ANACOM, Ericsson, FCT, Instituto Superior Técnico, Microsoft, POSC, PT Inovação, Rhode & Schwarz, University of Aveiro, and University of Beira Interior, Portugal. A copy of abstracts and the majority of presentations are available for download at http://www.e-projects.ubi.pt/ crossnet/workshop.html The coexistence scenario across heterogeneous networks should be seen by the end user as the ability to attain a plethora of multimedia services under a single platform in a ubiquitous and transparent fashion, providing the impetus for system solutions addressing network discovery, selection, con- nection, and reselection as the terminal equipment migrates between collocated networks. In the scope of CROSSNET, interoperability among B3G, IEEE 802.11, and IEEE 802.16 is investigated, since these technologies are widely seen as the enablers for converging the wireless and mobile worlds. By using the existing simulation platforms for different systems such as high-speed downlink packet access (HSDPA) and WiFi, a common radio resource management (RRM) module is being developed in order to provide a step toward network convergence to hide the heterogeneity between operators and technologies. CROSSNET has implemented an HSDPA system-level evaluation tool for evaluating RRM protocol performance. Furthermore, cross-layer scheduling and link adaptation provide key output to enhance the effective capacity and coverage in a more cost-effective way. The IEEE 802.11 WLAN (also known as WiFi) technology has seen high penetration in the broadband fixed wireless access (BFWA) market to provide data services to hotspot areas, mainly due to ease of network deployment and low cost. However, with the quality of service (QoS) constraints becoming evermore stringent, the IEEE opted to evolve the 802.11 standard to 802.11e, a WLAN technology for QoS support. The key enhancement in this evolved standard can be found in the MAC layer, which now provides support for differentiated service classes and proposes techniques to enhance the ability of the physical (PHY) layer to deliver time-critical multimedia traffic. CROSSNET is addressing innovative enhancement to IEEE 802.11e by pursuing research studies on the application of cross-layer signaling to improve QoS delivery, and provide more efficient usage of radio resources by adapting such parameters as arbitrary interframe spacing, a differentiated backoff procedure, and transmission opportunities, as well as acknowledgment policies. A key output from this work is also the development of an event-driven system-level simulator for IEEE 802.11e. Radio access technology (RAT) selection algorithms have been studied in the literature, and nowadays equipment with several RATs incorporated is already common. Results on the gains obtained by using WiFi as a backup network for HSDPA have been obtained. The coexistence of the two standards allows prevention of QoS deterioration when in a low mobility scenario. The proposed RAT selection algorithm is based on the load of each system, and the results show a gain of 60 percent on supported network load with the implementation of this QoS procedure over the HSDPA-alone system. As a consequence, when there is heavy load on the IEEE 802.11e network, acceptance of high-priority services will affect the delay in low-priority services like FTP. Worldwide Interoperability for Microwave Access (WiMAX) is the commonly used name for broadband wire- less access based on the IEEE 802.16 family of standards. WiMAX provides full QoS constrained service types with provisioning for high-data-rate applications targeted toward wide area coverage, and is widely considered to be a strong competitor in the mobile world. Following wireless trends toward ever more efficient networks, CROSSNET designed, implemented, and validated advanced scheduling algorithms based on a cross-layer framework architecture, exploiting information between the PHY and MAC layers. The scheduling policy, considered pivotal in controlling the trade-off between maximizing capacity and QoS delivery, uses cross-layer information to provide preferential treatment to mobile users according to QoS profile, channel conditions, and service classes. A key achievement from CROSSNET is the development of a C++ based mobile WiMAX system simulator that is being used to pursue this line of study.
- IEEE 802.11E Block Acknowledgement PoliciesPublication . Cabral, Orlando Manuel Brito; Segarra, Alberto; Velez, Fernando J.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.
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