By Tong Liu, Cisco Systems Inc
Prior to Full Duplex (FDX) DOCSIS, the downstream (DS) and the upstream (US) were scheduled independently, as the DS and the US transmissions were isolated from each other in frequency. In FDXDOCSIS however, the DS and the US operate at the same frequency and at the same time. Coordinated DS and US scheduling is required to avoid interference and to balance the bi-directional traffic need.
Fundamentally, FDX spectrum is directionally fluid with a unique set of constraints that confines the DS and US scheduling decisions. How to manage the FDX spectrum resource, maximize the DS and US throughput and maintain fairness is a big design and deployment challenge faced by both Cable Modem Termination System (CMTS) vendors and operators.
In this paper, we tackle this problem by studying the characteristics unique to the FDX spectrum, quantify the optimization objectives, and identify scheduling options to maximize both spectral efficiencies and fairness. The rest of the paper is organized as follows. Section 1 overviews the FDX operation principles and the scheduling constraints. Section 2 then examines the correlations between the DS and the US spectral efficiencies. Section 3 characterizes the FDX spectrum directional assignment and its impact on system throughput. Section 4 quantifies the FDX spectrum capacity gain with respect to the FDD spectrum capacity. Section 5 discusses fairness in the context of the FDX spectrum resource distribution hierarchy. Section 6 provides an illustrative example to demonstrate the FDX spectrum resource scheduling framework. A summary is provided at the end to conclude the paper.