Coding to Enhance Performance of Amplified Optical Communication Systems in the Presence of Noise Components of Optical Devices and Channel Interference
Sulaiman M. Abu-Gazleh
The applicability of single-mode fibers from the viewpoint of transmitted optical power limitation due to scattering and noise processes is studied. To deal with this applicability of fibers and consequently with lightwave systems performance, several parameters should be taken into consideration. The most important parameters affecting the performance of amplified optical networks are: channel frequency separation, total channel numbers, the maximum allowable signal power, the maximum transmission length, and the receiver sensitivity degradation. The effects of amplified spontaneous emission (ASE) noise, avalanche photodiode (APD) noise, thermal noise, and interference (crosstalk) for optical code division multiple access direct detection (OCDMA/DD) are examined. One such scheme is an optical orthogonal code division multiple access (OOCDMA) system.
In this paper, performance of amplified lightwave systems employing both conventional M-ary Quadrature Amplitude Modulation Subcarriers Multiple Intensity Modulation / Direct Detection (M-ary QAM-SCM-IM/ DD) and OCDMA/DD schemes have been analyzed. The analysis also incorporates the influence of code rates (weights) on the system performance. It is observed from analysis that for a given number of users, performance of OCDMA networks improves with the increase in the code weight. Furthermore, use of large code weight will give rise to better performance, but less number of simultaneous supportable users. On the other hand use of small code weight leads to a poor performance, but in this case the number of supportable users are large. Also, it is found that coding can increase the total channel number and eliminate error floor under a given bit error rate and receiver sensitivity. These systems employing optical amplifier have been studied and investigated. It is found that coding can increase the total channel number and eliminate error floor under a given bit error rate and receiver sensitivity. A performance comparison of QAM and OCDMA systems reveals that OCDMA can accommodate a larger number of subscribers and more simultaneous users than QAM.
Keywords: Fiber optic link, System performance, Optical amplifier, Noise sources, Noise components, Coding, Bit error rate, Sub-carrier system, Quadrature amplitude modulation, Detection, Receiver sensitivity, Optical devices, Lasers, Photo detectors.