New-Tech Europe Magazine | August 2017

High Directivity Couplers Isolate Upstream/ Downstream Paths in Full Duplex DOCSIS® 3.1 Systems

WeiPing Zheng, Steven Scheinkopf, Jeremy Cortez, and Brandon Kaplan, Mini-Circuits

Background: The Push toward Symmetric, Multi- Gigabit Broadband Service Continuous growth in demand for consumer and enterprise broadband data service is driving the efforts of cable industry researchers, operators, and hardware suppliers to extend the DOCSIS 3.1 standard to offer symmetric, multi-gigabit service over existing hybrid-fiber- coax (HFC) networks. The current version of the standard enables downstream capacity of up to 10 Gbps, but upstream capacity is still essentially limited to under 1 Gbps. DOCSIS 3.1 uses Frequency Division Duplexing (FDD) to partition the allocated spectrum (5 to 1220 MHz) for upstream and downstream signal traffic. The upstream bandwidth, typically from 5 to 85 MHz places inherent limitations on data capacity for the return path, posing a barrier for emerging applications requiring

Forward and Reverse Signal in Full Duplex DOCSIS 3.1 Systems Because network nodes are transmitting at high signal power and receiving at low signal power over the same frequencies, one of the unique challenges to realizing working Full Duplex DOCSIS 3.1 systems is the tendency of transmit signal to leak into the receive path. If upstream signal leaks into the downstream signal chain, for example, it can get fed back through the CATV amplifier resulting in intermodulation products and other kinds of interference. The system therefore requires circuit elements that allow forward and return signal to pass in close proximity through network nodes with enough isolation to prevent leakage between the paths. To address this problem, Mini-Circuits has partnered with broadband operators and hardware suppliers to

higher upstream speed. The industry has responded to this looming barrier by exploring the application of full duplex communication to the DOCSIS 3.1 standard, which would allow upstream and downstream signal traffic to utilize the same portion of spectrum at the same time, doubling the efficiency of spectrum use. Full Duplex DOCSIS 3.1 technology, once deployed over 1 GHz HFC networks, could ultimately achieve 10 Gbps capacity in both upstream and downstream directions. Since the announcement by CableLabs in 2016 of the commencement of Full Duplex DOCSIS 3.1 to an R&D phase project, CableLabs members and key suppliers have entered into a major collaboration to define the specification and develop new system architectures to achieve symmetric multi-gigabit performance over broadband networks. The Challenge: Isolating

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