L.A. Stations Decode Channel-Sharing Question
The FCC and the CTIA-The Wireless
Association believe that having two TV stations
share the same 6 MHz of spectrum
currently used by just one station will provide
broadcasters what they need to do business and open
up much desired spectrum for the wireless industry.
Right now they’re finding out if it can be
“APTS reached out to us on behalf of our
PBS community,” said Alan Popkin, director
of engineering for participant station KLCS.
The Association for Public Television Stations
is a lobbying group for the public television
industry, and Popkin explained that
APTS’ interest in the project was to further
public television’s knowledge by investigating
and evaluating the challenges and benefits
of channel sharing.
“Public television stations have always
embraced technology; they were the first
to caption, use descriptive video and offer
multicast services,” said Lonna Thompson, executive vice president, chief operating officer
and general counsel for APTS.
Popkin said the reason KLCS and KJLA
were chosen was due to their very different
content models. KJLA serves the Hispanic
minority population of Los Angeles and
KLCS as a PBS station serves “the underserved.”
Both agreed to participate because
of their shared mission to serve their viewers.
“What can you successfully put into a
19.39 Mbps channel and how do you do
that with the best engineering practices?”
Popkin articulated that this is a goal of both stations.
The technology to send multiple HD/SD
signals down a single channel has been around
for many years, but taking channels from
two different stations and combining
them created a whole host of
|Mt. Wilson is home to KLCS and KJLA’s antennas.
was to identify how to configure a
Program and System Information
Protocol table for multiple
channels originating from two separate
traffic systems. PSIPs manage
both program and commercial content
for each station. They needed
to make sure the event information
tables would parse out the
proper program descriptions to the
correct channels. What isn’t known
is how many TVs will then be able
to accurately display these.
Dane Eriksen, a consulting engineer
who follows trends in RF for
Hammett & Edison in San Francisco,
is closely watching how the channel
identification will be handled.
“Can the current PSIP code accommodate
two primary channels,
as opposed to just one primary
channel and multiple secondary
channels?” Ericksen asked. The
KLCS-KJLA combination may try
to fit both their 41.1-x and 49.1-x
primary and subchannels into two
virtual channels fed through a single
“Another concern is whether all receivers
built to current ATSC standards will respond
uniformly and if the PSIP can handle
two virtual channels in one RF channel,” Ericksen
Also of interest is a test to encode and
transmit H.264 content over the air. This is
not part of the current ATSC spec, though
many newer web-enabled TVs have H.264
decoders built in for streaming Internet content.
The question is whether there is a way
for the H.264 decoder to be accessed by the tuner, a technology solution that seems very
possible. By enabling more efficient compression
over the air, broadcasters could further
expand their offerings to their viewers.
It also raised an interesting question to
Popkin, “if H.264 works over the air, would
broadcasters be able to get away with using
a lower bandwidth MPEG-2 lifeline channel
and then offer more H.264 streams?” This is
a business and legal quandary that may arise
should the tests prove successful.
The other business and legal issue that
arises from changing current delivery
bitrates and formats is how to handle retransmission
agreements. This is the legal
stipulation where a cable or satellite provider
is supposed to be provided a signal of
a specific quality for retransmission through
their systems. Popkin does not see this as an
issue, however. “To meet retrans rules, stations
can provide other concurrent bitrates
via video fiber or data circuits to the cable or
satellite providers,” he said.
Broadcasters may have invented the original
broadcast standards, but it is the electronics
industry that today determines where the
technology will go. Broadcasters basically
have to broadcast to what the equipment
will receive. This is an important reason for a
productive partnership with the electronics
|(L to R) Alan Popkin and Roger Knipp of KLCS and Eddie Hernandez of KJLA
monitor the results of the stations’ channel sharing experiment.
“The CTIA funded
the project with
the latest encoder/
decoders for us to
see what could be
possible,” said Popkin,
who added that
and groups are
directly involved in
the overall experiment.
their full range of
TVs for reception
testing, to PBS loaning
their QoE measurement
gear, there is a concerted effort by
all parties to create a test that will result in
data that can be used by all involved.
“As digital compression rates continue to
improve, our stations will use their spectrum
to offer diverse programming streams, and educational and public safety data streams, as
well as other public services,” added APTS’s
Because each test station is only licensed
to broadcast specific content, as part of the testing they created a bench system that they
could compare to the OTA broadcast chain.
This was done to set a baseline for testing
other more challenging material such as
sports and other more bitrate-hungry video.
Popkin was pleased to discover that “we found no real degradation between over-theair
and the test bed’s digital streams.” This
gives his team the ability to truly try to first
“break” the program stream on the bench
system without affecting the over-the-air
Unlike cable and satellite media providers,
broadcasters do not control both sides of the
broadcast chain. If they want to add services
or channels they cannot just send their customers
a new box
“Broadcasters have a challenge in innovating,
as they control just the send end of the
pipe,” Popkin said. Thus broadcasters are at
the mercy of the manufacturers and what
functionality they will enable on their devices.
The mobile TV initiatives are good examples
of this where a lack of receiving devices
supporting their transmissions has led
to limited adoption of the new offering. For
broadcasters, moving forward in developing
new technologies will require continued
partnerships, more testing and the ability to
inform and communicate their goals through
the distracting chatter of government and industry
IN THE DETAILS?
The goal of the pilot program, announced
in late January, is to show that if implemented
in markets across the country—as part
of the upcoming incentive auction of television
broadcast spectrum—channel sharing
would allow over-the-air broadcasters to
continue providing—and enhancing—quality
content without impacting their viewers
while reducing infrastructure costs. Subsequently,
the spectrum relinquished by those
channel-sharing broadcasters would be auctioned
with some of the proceeds going to
those participating broadcasters to reinvest
in services to benefit their communities.
In preparation for the testing, which is
expected to wrap up this month, FCC Chairman
Tom Wheeler recently visited KLCS
(one of the two stations participating in
the test, KJLA is the other), where he saw
the station broadcast not only a single HD
channel but also multiple SD channels on
a single transmission path—an action he
called “game changing.” He was not around
for the next planned test which is to fit two
primary HD channels onto that same path.
But considering that public broadcaster
WETA, which is in Wheeler’s own backyard
in Washington, D.C., pioneered multicasting
years ago with a single HD primary channel
and multiple SD subchannels, this technical
demonstration should have been no surprise.
What Wheeler missed was in the details:
The true technical goals of the tests, and
how those results may affect and improve
broadcasters’ ability to maximize the use of
currently allotted spectrum.
Similarly, the CTIA began its press release
saying the “goal of the program” was
to show that squeezing two broadcasters
into one channel would provide motivation
for stations to broker deals in the incentive auctions to sell their spectrum to wireless
providers. These are the auctions where the
government hopes to make money by selling
broadcaster allotted spectrum space to
an eager and wealthy wireless industry.
This pro wireless stance once again
renews the debate of the value of providing
broadcasters use of spectrum
and what truly benefits the public
more. The FCC and CTIA view the
desire for more wireless devices and
services as justification for spectrum
re-allocation, where broadcasters believe
the public services they provide
justify the status quo.
In a cautionary response to the
project, the National Association of
Broadcasters expressed concern that
limiting spectrum access by channel
sharing may limit the industry’s ability
to “offer new and innovative services”
that also will benefit the public.
Looking closer at what public station
KLCS and commercial station
KJLA are actually doing may supply
data that will eventually benefit both
wireless and broadcast industries. It
not only demonstrates that a public/
private partnership can work, it also
shows how advances in technology
can overcome current technical challenges.
This type of success may eventually
provide solutions that will benefit
both industries as well as the public.
The test group in Los Angeles hopes to
present its results at the NAB Show next