By Richard S. Prodan, Ph.D., Comcast Cable
The advent of Full Duplex DOCSIS® (FDX) technology is here as realized in a custom ASIC successfully implemented in an operational FDX R-PHY node reference design. This ASIC is also currently being ported to a node design for trial deployments in Node + 0 networks. A version of this ASIC is also being adapted for a prototype FDX amplifier utilizing the same echo cancellation technology employed in the node.
The original constraint in the DOCSIS 4.0 FDX specification anticipated deployments exclusively in a passive Node + 0 network without amplifiers. The initial evaluation in a demonstration of the implemented prototype FDX R-PHY node incorporating the first FDX RPD ASIC exceeded performance expectations [2]. The resultant performance of the echo cancellation technology suggests use in an FDX amplifier as a “repeater” of bidirectional FDX signals.
This paper considers this implementation for an FDX amplifier. Why this greatly expands the use of FDX technology in conventional Node + X amplifier networks is introduced. How the FDX amplifier is implemented and the resulting performance greatly increasing upstream capacity is analyzed. The performance of cascading FDX amplifiers is shown. Finally, the path to upgrading existing Node + X cable networks when the next generation FDX amplifier ASIC currently under development becomes available is discussed.