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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
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
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
42 l New-Tech Magazine Europe