Name: | Description: | Size: | Format: | |
---|---|---|---|---|
3.46 MB | Adobe PDF |
Authors
Abstract(s)
A forte atenuação dos sinais eletromagnéticos na água é a principal razão pela
qual a exploração subaquática, a vigilância marítima e outras aplicações, atualmente
dependem de cabos submarinos para enviar ou receber dados de um terminal de
comunicação. Embora a comunicação acústica se tenha tornado o método de
comunicação sem fios padrão para as aplicações subaquáticas devido ao seu longo
alcance, elas incorrem em alto custo e têm baixas taxas de dados. A necessidade por
comunicações de alto débito binário e largura de banda estimulou a exploração de
métodos não acústicos que antes eram negligenciados devido às limitações de
distância.
Contrariamente aos sistemas acústicos e de radiofrequência, que apresentam
limitações como custo, velocidade de propagação das ondas e largura de banda
disponível, o que se traduz na taxa de transmissão de dados, a comunicação ótica
sem fios é apresentada como solução alternativa para ultrapassar as limitações
mencionadas. À vista disso, a solução proposta nesta dissertação baseia-se num
sistema de comunicação ótica de baixo custo, viável para as comunicações sem fio
subaquática à curta distância entre veículos não tripulados. Assim sendo, um sistema
transmissor baseado em LED de alto brilho de 3𝑊 com uma faixa de comprimento de
onda entre 460 – 470 𝑛𝑚 e um sistema recetor baseado em fotodíodo com uma
sensibilidade espectral entre 400 – 1100 𝑛𝑚, foram desenvolvidos e testados em
diferentes canais de comunicação, ao ar livre, num tanque de água doce e por fim na água
do mar. O resultado das experiências com o protótipo mostrou com sucesso que, na
presença da luz ambiente, a distância de transmissão - receção dos dados chega a 4,5
𝑚 e, na ausência da luz ambiente 5,50 𝑚 ambos com uma taxa de transmissão de
300 𝑏𝑝𝑠.
Por fim, o trabalho apresenta sugestões para trabalhos futuros de modo a
melhorar o desempenho, a eficiência e a robustez do sistema.
The strong attenuation of electromagnetic signals in water is the main reason why underwater exploration, maritime surveillance and other applications currently rely on underwater cables to send or receive data from a communication terminal. Although acoustic communications have become the standard wireless communication method for underwater applications due to their long range, they incur high cost and have low data rates. The need for high data rate and bandwidth communications has stimulated the exploration of non-acoustic methods that were previously neglected due to distance limitations. Contrary to acoustic and radio-frequency systems, which present limitations such as cost, wave propagation speed and available bandwidth, which translates into data transmission rate, wireless optical communication is presented as an alternative solution to overcome the mentioned limitations. In view of this, the solution proposed in this dissertation is based on a low-cost optical communication system, feasible for underwater wireless communications at short distance between unmanned vehicles. Therefore, a transmitter system based on 3W high-brightness LED with a wavelength range between 460 - 470 nm and a receiver system based on photodiode with a spectral sensitivity between 400 - 1100 nm, were developed and tested in different communication channels, outdoors, in a freshwater tank and finally in seawater. The result of the experiments with the prototype successfully showed that, in the presence of ambient light, the data transmission-reception distance reaches 4,5 m and, in the absence of ambient light 5,50 m both with a transmission rate of 300 bps. Finally, the work presents suggestions for future work in order to improve the performance, efficiency and robustness of the system.
The strong attenuation of electromagnetic signals in water is the main reason why underwater exploration, maritime surveillance and other applications currently rely on underwater cables to send or receive data from a communication terminal. Although acoustic communications have become the standard wireless communication method for underwater applications due to their long range, they incur high cost and have low data rates. The need for high data rate and bandwidth communications has stimulated the exploration of non-acoustic methods that were previously neglected due to distance limitations. Contrary to acoustic and radio-frequency systems, which present limitations such as cost, wave propagation speed and available bandwidth, which translates into data transmission rate, wireless optical communication is presented as an alternative solution to overcome the mentioned limitations. In view of this, the solution proposed in this dissertation is based on a low-cost optical communication system, feasible for underwater wireless communications at short distance between unmanned vehicles. Therefore, a transmitter system based on 3W high-brightness LED with a wavelength range between 460 - 470 nm and a receiver system based on photodiode with a spectral sensitivity between 400 - 1100 nm, were developed and tested in different communication channels, outdoors, in a freshwater tank and finally in seawater. The result of the experiments with the prototype successfully showed that, in the presence of ambient light, the data transmission-reception distance reaches 4,5 m and, in the absence of ambient light 5,50 m both with a transmission rate of 300 bps. Finally, the work presents suggestions for future work in order to improve the performance, efficiency and robustness of the system.
Description
Keywords
Comunicação ótica sem fio subaquática veículos subaquáticos autónomos modulação On-Off-keying optoelectrónica