Doppler spectrum type contribution to BER in fiber optic communication channel

Integrated ship communication systems require reliable and safe communication media that is suitable for fiber optic cables. This paper investigates such systems. The focus of this paper is on the research into the influences of different Doppler spectrum types to measure bit error rate in communications based on fiber optics. The results show that the highest BER is obtained for Asymmetrical Jakes and the lowest for the Jakes spectrum type. Although we are interested in communications aboard ships, the methodology can be applied to any fiber optic communication system

Equalização digital da dispersão cromática em sistemas de transmissão óticos coerentes

Mestrado em Engenharia Eletrónica e TelecomunicaçõesA crescente procura de largura de banda tem obrigado a área de comunicações óticas a explorar diferentes soluções, de forma a evitar a ”crise de capacidade” [1]. O investigadores têm trabalhado no sentido de atingir o equilíbrio entre os vários compromissos, repensando a forma como o sinal ótico é enviado e recebido, para que a perda de informação seja mínima ao longo do canal de propagação. No inıcio desta década, começaram a ser adotados formatos de modulação avançada, os quais apresentam elevada eficiência espetral, bem como deteção coerente, que permite extrair a informação da amplitude e da fase do campo ótico. Estas técnicas são complementadas pelo pós-processamento digital de sinal, que é atualmente muito importante na mitigação das distorções do sinal e imperfeiçoes do recetor. As distorções do sinal podem ser causadas, por exemplo, pela dispersão cromática na fibra. Esta dissertação engloba o estudo e simulação de um sistema de transmissão coerente PM-QPSK, bloco-a-bloco, fazendo uma abordagem detalhada dos conceitos supramencionados. O sistema foi então simulado na presença de dispersão cromática e de ruído, alternada e simultaneamente. Os resultados mostram que o sinal recebido apresenta uma distribuição quase Gaussiana em todos os casos. Com vista a recuperar o sinal transmitido, e no caso em que só se considerou o efeito da dispersão cromática, aplicou-se um filtro linear de resposta impulsional inversa à da fibra, conseguindo assim uma equalização digital perfeita do sinal recebido. Também foi implementado um filtro adaptado no receptor para minimizar o efeito do ruído, obtendo não uma equalização perfeita, mas ótima.The crescent demand on high bandwidth has been compelling the optical communications area to explore di erent solutions, in order to avoid the \capacity crunch" of the optical bres [1]. Researchers have been working towards reaching the best tradeo s balance, rethinking the way as the optical signal is sent and received, so the loss of information is minimum throughout the propagation channel. Advanced modulation formats became adopted in the beginning of this decade, presenting high spectral e ciency, as well as coherent detection, which allows extracting information from the amplitude and phase of the optical eld. These techniques are complemented by post-digital signal processing, which is nowadays very important at mitigating signal distortions and receiver imperfections. Those impairments result, for instance, of the chromatic dispersion at the bre. This dissertation covers the study and simulation of a PM-QPSK transmission system, block-by-block, approaching in detail the concepts mentioned above. The system was then simulated with chromatic dispersion and with noise, alternately and simultaneously. The results show that the received signal presents an almost Gaussian distribution in every case. In order to retrieve the transmitted signal, and in the case that only chromatic dispersion's e ect was considered, a linear lter was applied with an inverse impulse response of the bre, achieving such a perfect digital equalization of the received signal. A matched lter was also implemented in the receptor to minimize the noise e ect, obtaining not a perfect equalization, but an optimal one

MATLAB Simulink Simulation Platform for Photonic Transmission Systems

High speed and ultra-high capacity optical communications have emerged as the essential techniques for backbone global information transmission networks. As the bit rate of the transmission system gets higher and higher 40 Gb/s to 100 Gb/s the modeling of proposed modulation techniques is very important so as to avoid costly practical demonstration. The search for a universal modeling platform for such systems is urgent. Matlab Simulink has become the universal mathematical and modeling tools in most universities and research laboratories around the world. This paper thus describes the modeling techniques for advanced photonic transmission systems and Simulink is proven to be very effective platform for development of photonic communications systems due its comprehensive blocksets. The simulation is based mainly on the physical phenomena and understanding of its concepts of communications and photonics. Simulink models are given as examples of various sub-systems of the photonic transmission systems. Some simulated transmission performances are demonstrated as examples of final results obtained from Simulink models of the transmission systems