Power margin improvement for OFDMA-PON using hierarchical modulation

Abstract

We propose and experimentally demonstrate a hierarchical modulation scheme to improve power margin for orthogonal frequency division multiple access-passive optical networks (OFDMA-PONs). In a PON system, under the same launched optical power, optical network units (ONUs) have different power margins due to unequal distribution fiber lengths. The power margin of the PON system is determined by the ONU with the lowest power margin. In our proposed scheme, ONUs with long and short distribution fibers are grouped together, and downstream signals for the paired ONUs are mapped onto the same OFDM subcarriers using hierarchical modulation. In a pair of ONUs, part of the power margin of the ONU with short distribution fiber is re-allocated to the ONU with long distribution fiber. Therefore, the power margin of the ONU with the longest distribution fiber can be increased, leading to the power margin improvement of the PON system. Experimental results show that the hierarchical modulation scheme improves the power margin by 2.7 dB for an OFDMA-PON system, which can be used to support more users or extend transmission distance.

A Hierarchical Modulation Enabled SNR Allocable Delta-Sigma Digital Mobile Fronthaul System

“…The RRUs are divided into several groups according to different SNR requirements caused by different transmission capacities or distances. Similar to [9][10], a lower SNR required RRU is paired with another higher required one.…”

“…Similarly, HM adaptively adjusts the signal quality of the two links within a group according to the user demands. It has been reported to be applied in OFDM passive optical network (PON) with a 2.7 dB power margin improvement [9]. What's more, HM has also been proved with PAM4 format in PON downstream systems to increase network power budget by 3.5 dB [10].…”

Theoretical analysis of joint hierarchical modulation and physical layer network coding for next passive optical networks

“…It might be challenging to implement flexible and superior performance to improve throughput for ONUs. We can apply the hierarchical modulation (HM) [7] to transfer different classes of data in PON simultaneously. The HM is one of the techniques for multiplexing and modulating multiple data streams into one single symbol stream, where those multiple symbols are superimposed together before transmission.…”

Advanced modulation formats for 400-Gbps short-reach optical inter-connection

“…In recent years, various technologies in software and hardware layers have been proposed to improve the energy efficiency, including dynamic topology optimization for network topologies, adaptive link rate for wired access networks and hybrid hierarchical base station deployment for wireless access networks etc [5]. Recently, there have been many studies on how to improve the energy-efficiency of the SR-ONs, such as [6][7][8][9][10][11][12]. In [6,7], sleep/doze strategies of optical network units (ONUs) are employed for the energy-efficient passive optical networks (PONs).…”

“…The bandwidth can be allocated dynamically to fit the traffic transmission. In [8], hierarchical modulation is proposed to improve the power margin of ONUs far from the optical line terminal (OLT). Energy-efficient physical topologies for the optical transport networks (e.g.…”