Análise de desempenho de redes ópticas utilizando o código corretor de erro Reed-Solomon

Abstract

The demand for telecommunication services has been growing rapidly in recent years, as well the number of studies in order to increase the capacity of transmission of communications networks. One of the best options is to use optical communications systems, because they allow high transmission rates. However, this type of system suffers with degradation of the optical signal due to unwanted effects of the optical fiber and noise inherent to the transmission process. In order to address this problem Forward Error Correction (FECs) are used. An example of FEC widely used in optical communications is the Reed-Solomon (RS) codes, designated by the nomenclature RS(n,k), where n is the total number of code symbols in the coded block, k is the number of data symbols to be coded, and n-k determines the number of redundancy symbols inserted in the coding process. A Reed-Solomon decoder can correct up to t wrong symbols, where 2t=n-k. In this context, this work sought to evaluate the performance of an optical network with wavelength division multiplexing (WDM), when different coding lengths and redundancy of the RS code are used for error correction. The system performance was evaluated in terms of the so-called "coding gain", defined as the reduction of the E_b/N_0 (in decibels) generated by the coding, in relation to E_b/N_0 required by the system without using the FEC, to achieve the same bit error rate (BER). The eye diagram was also used to demonstrate the improvement generated by the FEC. After coding implementation, it was possible to verify that in general, all coding lengths and redundancies of RS code provided the WDM optical system a performance improvement, reducing the required power requirements to achieve better BERs. As expected, the codes with the highest degree of redundancy were the ones that generated the best results, such as the RS (255,191) and RS (63,31) coding, which generated approximately 9 dB and 8 dB respectively, of coding gain.