Full-duplex DOCSIS: A Modem Architecture for Wideband (>1GHZ) Self-interference Cancellation for Cable Modem Termination Systems (CMTS)

摘要

In this paper, we design and study an architecture for realizing full-duplex cable modem termination system (CMTS) for DOCSIS 3.1 networks. The main echo (self-interference) in the upstream path of CMTS is the downstream signal that leaks through the splitter at CMTS, while the rest of the echoes are the reflections from the cable-modem taps. The proposed architecture addresses two main challenges in achieving wideband self-interference cancellation. The first challenge is the presence of high-powered echoes with large delays. In our architecture, a passive adder cancels all the echoes in analog-domain. The sum of echoes is locally generated in base-band, which is then sent as an input to the adder via an additional DAC. The second challenge is the presence of transmit-noise, which becomes significant for wideband systems. In our architecture, the transmit-noise is estimated and canceled using the power-amplifier output as reference, for which we employ an additional ADC. Simulations based on the measurements from a test cable plant show that over 10 Gbps upstream rates can be achieved with the proposed full-duplex CMTS architecture. When ADC has a resolution of over 12 bits, upstream rate without analog-cancelation is found to be at least 90% of that of the case with large analog-cancelation.