Abstract
Coherent receivers, with advanced and low-complexity digital signal processing (DSP), have the advantage of increasing the loss/power budget of next generation-long-reach passive optical networks (NG-LRPONs). This reduces the network capital expenditures by eliminating or reducing the number of amplifiers to be installed between the optical line terminal (OLT) and the optical network units (ONUs). In this paper, we investigate the complexity and convergence speed of two adaptive equalization and/or pre-emphasis strategies for mitigating chromatic and polarization mode dispersions (CD and PMD) in NG-LRPON. We first identify two potential deployment strategies of equalization and/or pre-emphasis. The first equally splits the signal processing in the OLT and ONU; however, the second concentrates most of DSP in the OLT trying to reduce the cost and alleviate the complexity of ONUs. Our investigation shows that the second strategy achieves 50 % faster convergence rate in terms of number of symbols for 16QAM/5 Gbaud. Moreover, we apply the enhanced set membership filtering (SMF) technique, recently introduced for next generation wireless communications, to our LR-PON in order to reduce the update rate of equalizers' taps, hence reduce the calculation complexity of the OLT and ONUs. Our results show that by employing SMF technique a substantial reduction in the number of mathematical operations needed to attain convergence is achieved. Simulation results reveal that our proposed SMF can reduce the equalizers' update rate, hence calculation complexity, by 55 % for 16QAM and 75 % for QPSK with marginal degradation of the BER.