Understanding LTE-Unlicensed // July 2015
Editor's Note
LTE-U Attracts
Controversy and
Industry support
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Can LTE and Wi-Fi Coexist in the Same Spectrum Band?
Although LTE-U is designed to play nice in unlicensed spectrum and avoid interference
with Wi-Fi, some in the industry are skeptical.
By Jason Bovberg
The primary challenge for operators and vendors
engaging in the debate about LTE-U will be to prove
that LTE-U/LAA can coexist with Wi-Fi in the
unlicensed spectrum band. Wi-Fi senses channel
activity before starting a transmission and then backs
off if the channel is occupied. This technology is called
Listen Before Talk (LBT)—a technology that LTE-U
doesn't implement. LAA, the 3GPP-standardized
version of LTE-U, will presumably solve this challenge
and ensure the fair use of spectrum by including LBT.
However, LTE-U, as developed by Qualcomm and the
LTE-U Forum, does not support LBT.
"Instead," said Ahmed Ali, Research Analyst, ABI
Research, "it uses an algorithm called Carrier Sensing
Adaptive Transmission (CSAT), which is a form of
time sharing (of the channel). From Qualcomm and
other LTE-U proponents' point of view, this is 'fair,'
but I still believe that there will be a negative impact
on Wi-Fi. First, CSAT doesn't sense the channel
before transmitting, so it can still interrupt Wi-Fi
transmission; and second, transmission period and
resource allocation are completely controlled by
LTE-U in this case."
The promise of LTE-U is shadowed by this
coexistence controversy. Although LTE-U is designed
to play nice in the unlicensed spectrum and to avoid
interference with other exiting standards such as Wi-Fi,
some in the industry remain skeptical.
Complementary technology?
Monica Paolini, analyst, Senza-Fila, is the author
of the comprehensive report "LTE unlicensed and
Wi-Fi: moving beyond coexistence." She believes
LTE-U adds just as much of a burden on the spectrum
band as another Wi-Fi access point (AP). In terms of
congestion, whether you have Wi-Fi or LTE-U doesn't
matter. "Spectrum is what it is," she said, "and we
have to share it." From this perspective, LTE-U does
