Performance Tolerance of IMDD DFMA PONs to Channel Frequency Response Roll-Off

Abstract

The impacts of the channel frequency response rolloff effect on upstream optical OFDM transmission performance in digital filter multiple access (DFMA) passive optical networks (PONs) based on intensity modulation and direct detection (IMDD) are investigated, in terms of BER versus received optical power performance, ONU transmission capacity, ONU launch power variation (LPV) range and inter-ONU sample timing offset (STO). The effect of signal bandwidth is also explored by comparing tolerance to the channel roll-off effect for two different signal bandwidths. Over all of the aforementioned aspects, good agreements are obtained between numerical simulations and experimental measurements. The results provide important insights into channel roll-off-induced performance dependencies to facilitate cost-effective designs of both DFMA transceivers and IMDD DFMA PONs.

Experimental Demonstration of a Real-Time Digital Filter Multiple Access PON With Low Complexity DSP-Based Interference Cancellation

“…• The low cost associated with large scale, mass-produced digital integrated circuits can keep PON capital expenditure (CAPEX) levels commercially viable. A DFMA PON, however, can suffer severe performance degradation, mainly due to a non-flat physical channel frequency response with significant roll-off, which results in cross channel interference (CCI) [7,8]. Channel roll-off is determined by factors such optical fiber length, optical and RF component characteristics and the sinc response associated with zero-order hold DAC/ADCs.…”

“…1. Top level DSP architecture of the 4-channel CCIC-enabled DFMA PON transceiver operating in different sub-wavelength bands is not needed for the purpose of maintaining channel orthogonality, however if the OLT employs a common ADC to receive all channels then the timing of all channels and therefore ONUs, must be aligned [7]. It is possible for an ONU to implement multiple SFs/MFs for multi-channel operation, and multiple ONUs can also share the same physical channel in the time domain [13].…”

“…4. This can be due to differences in the sub-wavelength band frequency response profiles [7], as here (in [8]) each sub-wavelength band occupies half (all) of the 1GHz aggregate signal bandwidth. Also, the real-time DSP hardware employs fixed-point calculations (max 12 bit) in comparison to the high precision, floating-point calculations of the off-line processing approach.…”

Real-time experimental demonstration of DSP-enabled soft-ROADMs with multi-level flexible add/drop functions for cloud access networks

“…In the add operation experiment, the direct-detection (DD)-induced optical beat interference (OBI) effect can occur when operating at similar nominal wavelengths, a wavelength spacing of 0.3nm is therefore employed between the two light sources, as this is sufficient to eliminate the OBI effect [23]. It is also worth noting that the end-to-end optical connections established in the add operation experiments exhibit frequency response roll-off, as detailed in Table 1, which can lead to non-perfect channel orthogonality-induced cross-channel interference (CCI) and subsequent overall system performance degradations [24,25]. This effect is however strictly transmission system-related and not dependent on the soft-ROADM add operation performance.…”

A Review of DSP-Based Enabling Technologies for Cloud Access Networks

“…Not only is correct sample timing critical in the ROT receiver, but it is also critical in the ROT transmitter for the case of multipoint-to-point (MPTP) networks where orthogonal sub-bands are combined in the optical domain [15]. In all of our experimental demonstrations manual sample timing alignment is employed, however investigations into the effect of sample timing offset (STO) in point-to-point and MPTP networks has been investigated [16] for different levels of channel frequency response roll-off. Figure 4 illustrates the DSP architectures of the demonstrated FPGA-based ROTs incorporating on-line reconfigurable digital orthogonal filters.…”