IEEE Spectrum April, 2014 - 18

SatelliteS and
SimulationS track
miSSinG methane
europe is spending €45 million to correctly
gauge emissions of the greenhouse gas
Methane emissions from oil and gas extraction, herding livestock,
and other human activities in the United States are likely 25 to 75 percent
higher than the U.S. Environmental Protection Agency currently recognizes,
according to a meta‑analysis of methane emissions research published recently
in Science. While experts in remote sensing debate the merits of this and other
recent challenges to the EPA's numbers, definitive answers are already on
order via a high‑precision Earth observation satellite to be launched next year.
The intensifying methane emissions debate has profound implications for cli‑
mate and energy policy. Natural gas consumption is rising, and methane's global
warming impact is more than 30 times as much as that of carbon dioxide, molecule
for molecule, and second only to carbon dioxide's in today's net climate impact.
Greenhouse gas inventories such as the EPA's quantify emissions from the
bottom up. They assume a leakage rate for each known source type and add up
the sources. The EPA's figures are being challenged by studies employing top‑
down methods, which use "inverse modeling" to transform point measurements
of atmospheric methane into emissions estimates. Models of airflow are used
to predict where measured methane is coming from and how fast it is flowing.
Conclusions from the meta‑analysis research, led by Stanford University
energy resources expert Adam Brandt, track closely the results of the most
recent and most comprehensive measurement‑based estimate of nationwide
methane emissions. The latter, published in November in the Proceedings of the
National Academy of Sciences by a multi‑institution
Do you Smell SomethiNG?
team of U.S.‑based scientists, relies on more than
A satellite might determine
12 000
air samples collected from towers across
whether cattle or oil and gas wells
the United States and flights by research planes
are the bigger climate culprits.

istockphoto

nEwS

Perlman has claimed that pCell technol‑
ogy could eventually increase the capacity
of today's cellular networks as much as a
thousandfold. But experts say that any per‑
formance gains will be limited by the pro‑
cessing capability at the data center and
the speed and reliability of links to the ac‑
cess points. "You should be able to collect
channel information, compute the signals,
and send them back to the transmitters in
less then 10 milliseconds," USC's Caire says.
"According to our simulations, we see gains
of about a factor of 10 for realistic scenarios.
Much more than that, I'm skeptical."
At Columbia University in New York City,
Perlman demonstrated pCell technology
communicating with 4G LTE phones and
other devices. Compatibility with LTE would
allow users to roam seamlessly between the
two networks without having to buy new
handsets. Artemis's engineers achieved this
feat by simulating LTE base stations in soft‑
ware, using these virtual radios to inform the
waveform calculations. However, MU-MIMO
experts argue that such compatibility will
be much more difficult to maintain in real‑
world environments.
Artemis is manufacturing pCell access
points with small‑cell provider PureWave
Networks and is planning for large‑scale tri‑
als in San Francisco. The company expects
commercial rollouts by the end of 2014.
Wireless experts say that Artemis has yet to
prove it can overcome several difficult obsta‑
cles, including the large‑scale coordination of
transmissions from many access points and
the integration of pCell clusters into existing
cellular networks. "These are rigorous engi‑
neering challenges," says Zhouyue "Jerry" Pi, a
senior director of Samsung Research America
in Dallas. "It's not easy to make this kind of
distributed MIMO work and create benefits."
Still, some experts concede that technolo‑
gies like pCell would make sense in congested
hot spots such as airports, sports stadiums,
and city centers-places where operators are
already investing in dense clusters of small
cells and where users don't move around
much. "But is it really going to revolutionize
the data capacity of the whole world?" Pi asks.
"I doubt that." -a r iel bleicher

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Table of Contents for the Digital Edition of IEEE Spectrum April, 2014
