By Hang Jin & John Chapman, Cisco Systems
Full duplex (FDX) DOCSIS® allows the downstream and upstream to use the same radio frequency (RF) spectrum at the same time, leading to ~100% increase of spectral efficiency. With FDX DOCSIS, the upper band edge of the upstream spectrum can be extended beyond 204 MHz, leading to five to 10 times increase in upstream throughput. The downstream throughput is also increased as the use of FDXDOCSIS can eliminate the crossover band of current frequency division duplex (FDD) systems and push the low band edge of the downstream below 258 MHz. Using the 10 MHz to 1.2 GHz spectrum, full duplex DOCSIS has the capability to provide 10 Gbps throughput for the downstream and 5 Gbps throughput for the upstream.
As the downstream and upstream spectrums overlap in FDX DOCSIS, interference occurs between transmission and reception. Thus, interference mitigation is a key enabler for supporting FDX DOCSIS.
Echo cancellation (EC) is required in FDX systems to suppress the interference that is coupled or leaked from the transmitter to the receiver as they operate on the same frequencies. Cisco invented and prototyped FDX DOCSIS echo cancellation algorithms, and demonstrated them in August 2016 at the CableLabs Summer Conference.
This paper explains the types of interference that occurs in FDX DOCSIS operation and the corresponding echo cancellation techniques required. The paper is organized as follows. Section 1 explains the basics of FDX DOCSIS operation. Section 2 explains the challenges with FDX DOCSIS operation: the interference from transmitter to receivers and the interference among cable modems (CMs).
Interference cancellation must be implemented for supporting FDX DOCSIS operation. Section 3 explains the network topology for supporting FDX DOCSIS. The details on the interference types and the corresponding echo cancellation techniques are given in 4-7. Section 8 explains the echo cancellation lab prototype system and test results, and Section 9 explains the live FDX DOCSIS proof of concept (PoC) demonstration system.