Real-Time Demonstration of Concurrent Upstream and Inter-ONU Communications in Hybrid OFDM DFMA PONs

Abstract

This letter presents the first real-time experimental demonstration of concurrent upstream and inter-ONU communications in a hybrid OFDM DFMA PON, enabled by a simple low-cost alteration to the remote node. Real-time FPGA-based DSP, incorporating a 128-pt FFT and a joint sideband processing technique, is used to demultiplex different sub-wavelength channels at the ONU and OLT receivers. The simple modification in the remote node removes the need for direct user-to-user data to pass via the OLT and core network thus providing ultra-low latency inter-ONU connectivity to support a variety of newly emerging latency sensitive 5G services. The presented PON is validated with two subwavelength bands, each capable of carrying one of two possible orthogonal channels ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I$ </tex-math></inline-formula> or <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> ). The dynamic channel and subcarrier allocation allows flexible allocation of PON capacity between upstream and inter-ONU links for dynamic on-demand capacity allocation and also performance optimisation according to the different length dependent link characteristics. Moreover, the backscattering effect associated with upstream signals is shown to have negligible effect on the BER performance of the inter-ONU communications.