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Authors
Advisor(s)
Abstract(s)
Um dos aspetos fundamentais para o desenvolvimento de uma rede de comunicações
móveis é o planeamento das áreas de cobertura de cada estação base.
Esta predição de sinal, estimada por modelos de propagação, tem de ser o mais
próximo da realidade possível e implica o conhecimento de diversos fatores que
influenciam a propagação num determinado ambiente. As comunicações em linhas
ferroviárias localizam-se, muitas vezes, em ambientes rurais com significativa
variação de perfis de terreno.
O Irregular Terrain Model (ITM) é um modelo que se apresenta promissor neste
tipo de situações porque tem em especial consideração as características do terreno
numa determinada área geográfica, assim como alguns fatores ambientais e
estatísticos.
O objetivo deste trabalho reside na análise da capacidade de predição de sinal
deste modelo. Neste sentido, foi implementado um software capaz de comparar
o desempenho do ITM com outro muito utilizado neste tipo de ambiente, o
Okumura-Hata, e escolhido um troço da linha da Beira Baixa caracterizado por
irregularidades no terreno bastante acentuadas.
Inicialmente, o ITM foi otimizado para o tipo de ambiente analisado através da
modificação de alguns parâmetros. De seguida, em oito estações base desta linha
ferroviária, desde Belver a Ródão, foram realizadas comparações entre ambos os
modelos de propagação e medidas a que se teve acesso. Analisaram-se, ponto a
ponto e para cada percurso, os resultados de nível de sinal predito face à realidade,
recorrendo a estatísiticas de erro.
Os resultados obtidos suportam a ideia de o ITM ser um modelo promissor na predição rádio em ambientes rurais com muitos desníveis no terreno, tendo apresentado
um desempenho significativamente melhor que o Okumura-Hata na maioria
das situações analisadas, assim como estimativas próximas às medidas registadas.
No entanto, destaca-se a dificuldade em lidar com obstruções significativas
na linha de vista de transmissão, principalmente em distâncias inferiores a
1 quilómetro, chegando a demonstrar desvios de 10 a 20 dB face às medidas.
One of the main aspects for the development of a mobile communications network is the planning of the coverage areas of each base station. This signal prediction, estimated by propagation models, has to be as close to reality as possible and implies the accountability of several factors that influence the propagation in a given area. Communications on railways are often located in rural areas with significant variation of terrain profiles. The Irregular Terrain Model (ITM) presents itself as a promising model in this type of situation because it takes into account the characteristics of the terrain in a given geographical area, as well as some environmental and statistical factors. The objective of this work lies in the analysis of the signal prediction quality of this model. For this purpose, a software capable of comparing the performance of ITM with another one widely used in this type of environment, Okumura-Hata, was implemented and a section of the Beira Baixa railway was chosen, being characterized by rather sharp irregularities in the terrain. Initially, the ITM was tuned for the type of environment analyzed through the modification of some parameters. Then, in eight base stations of this railway, from Belver to Ródão, comparisons were made between both propagation models and measures. The results of the predicted signal level were analysed, point by point and for each path, using parameters of statistical error. The results obtained support the idea that ITM is a promising model in rural areas with many terrain unevenness, having presented a significantly better performance than Okumura-Hata in most of the situations analyzed, as well as predicted signal levels very close to the measures recorded. However, the difficulty in dealing with significant obstructions in the transmission line-of-sight is highlighted, especially at distances of less than 1 kilometer, even showing deviations of 10 to 20 dB from the measurements.
One of the main aspects for the development of a mobile communications network is the planning of the coverage areas of each base station. This signal prediction, estimated by propagation models, has to be as close to reality as possible and implies the accountability of several factors that influence the propagation in a given area. Communications on railways are often located in rural areas with significant variation of terrain profiles. The Irregular Terrain Model (ITM) presents itself as a promising model in this type of situation because it takes into account the characteristics of the terrain in a given geographical area, as well as some environmental and statistical factors. The objective of this work lies in the analysis of the signal prediction quality of this model. For this purpose, a software capable of comparing the performance of ITM with another one widely used in this type of environment, Okumura-Hata, was implemented and a section of the Beira Baixa railway was chosen, being characterized by rather sharp irregularities in the terrain. Initially, the ITM was tuned for the type of environment analyzed through the modification of some parameters. Then, in eight base stations of this railway, from Belver to Ródão, comparisons were made between both propagation models and measures. The results of the predicted signal level were analysed, point by point and for each path, using parameters of statistical error. The results obtained support the idea that ITM is a promising model in rural areas with many terrain unevenness, having presented a significantly better performance than Okumura-Hata in most of the situations analyzed, as well as predicted signal levels very close to the measures recorded. However, the difficulty in dealing with significant obstructions in the transmission line-of-sight is highlighted, especially at distances of less than 1 kilometer, even showing deviations of 10 to 20 dB from the measurements.
Description
Trabalho final de mestrado para obtenção do grau de Mestre em Engenharia de Eletrónica e Telecomunicações
Keywords
Irregular Terrain Model Longley-Rice Okumura-Hata Modelos de propagação Propagation models Comunicações ferroviárias Railways communications
Citation
PRIOR, Pedro Manuel Morão - Estimação de cobertura rádio em comunicações ferroviárias recorrendo ao irregular Terrain Model. Lisboa: Instituto Superior de Engenharia de Lisboa, 2021. Dissertação de mestrado.
Publisher
Instituto Superior de Engenharia de Lisboa