Will LTE Fuzz Up Cable?

The next-generation wireless-broadband
technology being widely deployed in the U.S. could be a
headache for cable operators — even if a relatively small one.

Testing performed in conjunction with Virgin Media,
Britain’s largest cable operator, showed that Long Term
Evolution wireless equipment can interfere with many
set-tops and cable modems. The tests were commissioned
by the United Kingdom’s Office of Communications, the
country’s telecommunications regulatory authority, to determine
the effect of LTE operating in the 800-Megahertz
band on cable TV.

The results: Seven out of the nine set-tops tested were susceptible
to interference from LTE user equipment operating
at full power, and all 12 of the cable modems were disrupted.

On the other hand, the LTE equipment was tested at a distance
of 1 meter, meaning a customer would have to place
an LTE phone practically on top of a set-top or cable modem
to replicate the problems.

The testing and other studies “suggest that mobile handsets
located close to [set-top boxes] could cause interference
due to limitations in the [radio-frequency] screening of the
tuner section,” the report said.

In the U.S., Verizon Wireless has already deployed LTE
in 38 markets covering more than 110 million Americans; it
expects to double coverage over the next 18 months. AT&T
plans to begin launching LTE in mid-2011 and has said it
will cover up to 75 million people by year-end.

In Europe, the frequency band for LTE is 790 to 862 MHz.
Th e Ofcom report noted that cable-TV interference was observed
only for channels that used that same frequency
range. “[N]o adjacent, local oscillator or image channel interference
was observed,” the report said.

Cable modems appeared to be more at risk: 10 of the 12 cable
modems failed to conform to suggested European limits
for signal immunity in the tested LTE frequency range. Only
one set-top of the nine didn’t meet suggested limits.

The Ofcom report concluded that “some simple measures
could be taken to improve the resilience” of cable modems,
such as additional screening of the RF circuitry.

In general, coaxial cable is highly resistant to signal interference
because the central core is covered by a metallic
shield. The Ofcom test, though, measured the effect of LTE
on customer-premises equipment.

The testing was conducted by British consulting firm
Cobham Technical Services over a seven-week period at
Virgin Media’s lab facility in Birmingham, U.K., starting in
April 2010. The measurements were taken from the front,
side and back of each set-top, and from the front and side of
each cable modem.

The report didn’t identify the manufacturers of the cable
modems and set-tops used by Virgin Media that were part
of the test. The MSO’s suppliers historically have included
Cisco Systems, Motorola, Pace, Samsung Electronics and
Ubee Interactive.

All of the equipment tested complies with existing European
regulations, Cobham Technical Services noted.