Planeamento celular e engenharia de teletráfego em redes móveis celulares

Abstract

Nos últimos anos, o desenvolvimento de novas tecnicas de processamento digital do sinal, por um lado, e os avanços tecnológicos na Area da microelectrónica que possibilitaram a implementação dos mesmos, por outro, levaram a uma miniatunzaq5.0 dos terminais móveis utilizados, quando comparados com os terminais analógicos utilizados nas redes de primeira geração. Este efeito, que permnitiu uma melhoria significativa na qualidade da transmissão de voz e dados, aliado a uma crescente diversificação de novos serviços disponibilizados aos assinantes, levou a um aumento explosivo da taxa de penetração do serviço de radio móvel celular. Da mesma forma, o tráfego oferecido, que antes era essencialmente de mobilidade, uma vez que os terminais instalados no interior das viaturas se destinavam A efectivação de chamadas quando em movimento nas estradas, passou a ser também do tipo estacionário. 0 tamanho reduzido, a elevada autonomia e portabilidade dos novos terminais permitem aos assinantes a efectivação de chamadas telefónicas nos mais variados lugares: dentro de casa, em centros comercias, ou mesmo enquanto se deslocam nas ruas. 0 resultado de todo este processo de mudança foi um aumento explosivo do tráfego oferecido que passou a condicionar a qualidade do serviço prestado ao cliente e veio trazer novos desafios no projecto e implementação deste tipo de redes.

In the last few years, the development of new methods on digital signal processing by one hand, and the technological outcomes in microelectronics, which made that possible, by another, carried out the decrease in the size of the mobile terminals when compared with the ones used in the analogue networks of the first generation systems. This effect, which allowed a significant improvement on the transmission of quality voice and data, coupled with an increasing mixture of new services madeavailable to the subscriber, provoked an explosion of the service penetration rate. By the same way, the offered traffic, which was in its whole of mobility type in the past, since the terminal sets were designed for in-car use, turned out to be a stationary one. The smaller size, longer batteries life and ease of portability of the new handsets allow subscribers to carry out calls in a mixture of places: inside home, in shopping centres or even while on the move on the streets. The final result of this whole changing process was a tremendous increase on the traffic being offered. This process impose restrictions on the quality of the service made available to the subscriber and brought up new challenges in the design and implementation of these new networks. The main purpose of this work is to analyse the implications that the increasing demand on the offered traffic have in the design and implementation of second generation mobile cellular networks, particularly to the maintenance of the quality of the service made available to the subscriber. For this reason a detailed analysis of a group of techniques and methods of cellular planning is camedout. Some of these techniques are already being implemented by many operators. Some signal propagation models are analysed, since these models allow the calculation and derivation of the parameters that describe the network performance, thus being used in the network planning process: CO-channel and adjacent channel interference factors. A few planning techniques are analysed and compared to each other: cell splitting, sectorization, overlaid/und.erlaid, implementation of frequency hopping, load sharing, implementation of hierarquical networks (microcells and picocells), discontinuous transmission - uplink and downlink). Some models for the calculation of the probability of blocking of new calls for different methods of channel allocation: fixed (fixed channel allocation), dynamic (dynamic channel allocation) and hybrid (hybrid channel allocation) allocation methods. A few methods for the improvement of the probability of blocking of calls are also introduced: guard channels (cut-off channels) and queuing of new and handover calls. Keywords: Second generation cellular mobile networks, grade of service, CO-channel and adjacent interference factor, handover calls, f?equency reuse, call blocking, cellular planning methods, teletraffic models, signal propagation models.