Simplified turbo equalizer for bandwidth-limited 50G passive optical networks

Abstract

Owing to digital signal processing, 50G passive optical networks (PON) in cost-sensitive scenarios can be implemented utilizing low-cost devices. However, the limited bandwidth of low-cost devices degrades the bit error ratio performance. Meanwhile, although 50G PON operates in the O band with a low chromatic dispersion (CD) coefficient, the cumulative CD cannot be ignored for a 50G on-off keying signal, especially in the 40km access scenario. This paper proposes a simplified Turbo equalizer based on maximum-log-maximum a posteriori (Max-Log-MAP) module for 50G PON to deal with the inter-symbol interference (ISI) caused by the low-cost devices and CD. The Max-Log-MAP module replaces the complicated logarithms and exponents with simple comparisons without degrading performance, greatly decreasing the complexity compared to the conventional Log-MAP module. The experimental results show that the receiver sensitivity improvement of approximately 0.1dB, 0.25dB, and 0.5dB can be obtained by the simplified Turbo equalizer for 0km, 20km, and 40km access scenarios, respectively. Therefore, the simplified Turbo equalizer shows great promise for the bandwidth-limited 50G PON.