IEEE Wireless Communications • February 2016
38
1536-1284/16/$25.00 © 2016 IEEE
The author is with Uni-
versitat Pompeu Fabra,
Barcelona
AbstrAct
IEEE 802.11ax-2019 will replace both IEEE
802.11n-2009 and IEEE 802.11ac-2013 as the
next high-throughput WLAN amendment. In this
article, we review the expected future WLAN
scenarios and use cases that justify the push for a
new PHY/MAC IEEE 802.11 amendment. After
that, we overview a set of new technical features
that may be included in the IEEE 802.11ax-2019
amendment, and describe both their advantages
and drawbacks. Finally, we discuss some of the
network-level functionalities that are required to
fully improve the user experience in next-gener-
ation WLANs and note their relation with other
ongoing IEEE 802.11 amendments.
IntroductIon
IEEE 802.11 wireless local area networks
(WLANs) [1] are a cost-efficient solution for
wireless Internet access that can satisfy most cur-
rent communication requirements in domestic,
public, and business scenarios.
Similar to other wireless technologies, WLANs
have evolved by integrating the latest technolog-
ical advances in the field as soon as they have
become sufficiently mature, aiming to continuous-
ly improve spectrum utilization and raw WLAN
performance. IEEE 802.11n-2009 adopted sin-
gle-user multiple-input multiple-output (SU-MI-
MO), channel bonding, and packet aggregation.
Those mechanisms were further extended in IEEE
802.11ac-2013, which also introduced downlink
multi-user (MU) MIMO transmissions. In addi-
tion, new amendments such as IEEE 802.11af-
2013 and IEEE 802.11ah-2016 are further
expanding the application scenarios of WLANs,
which include cognitive radio, long-range commu-
nication, advanced power saving mechanisms, and
support for machine-to-machine (M2M) devices.
Partly because of their own success, next-gen-
eration WLANs face two main challenges. First,
they must address dense scenarios, which is
motivated by the continuous deployment of new
access points (APs) to cover new areas and pro-
vide higher transmission rates. Second, the cur-
rent evolution of Internet usage toward real-time
high-definition audio and video content will also
significantly increase users’ throughput needs in
the coming years.
To address those challenges, the High-Effi-
ciency WLAN (HEW) Task Group [2] is current-
ly working on a new high-throughput amendment
named IEEE 802.11ax-2019. This new amend-
ment will develop new physical (PHY) and medi-
um access control (MAC) layer enhancements
to further improve the WLAN performance,
with a focus on the throughput and battery
duration. This article overviews some of those
new enhancements, and describes the potential
benefits and drawbacks of each one. We have
grouped these enhancements into four main cat-
egories: spatial reuse, temporal efficiency, spec-
trum sharing, and multiple-antenna technologies.
Moreover, we also discuss several key system-lev-
el improvements for next-generation WLANs, as
in addition to the IEEE 802.11ax-2019 amend-
ment, they will likely implement other in-prog-
ress amendments such as IEEE 802.11aq-2016
(pre-association discovery of services), IEEE
802.11ak-2017 (bridged networks), and IEEE
802.11ai-2016 (fast initial link setup time) to sat-
isfy the created expectations.
scenArIos, use cAses, And
r
equIrements
The forecast number of devices and networks,
and traffic characteristics and user demands for
the 2020–2030 decade motivate the development
of a new PHY/MAC IEEE 802.11 amendment to
cope with the new challenges and usages WLANs
will face [2].
One of the most representative characteris-
tics of WLANs is the use of carrier sense multiple
access with collision avoidance (CSMA/CA) as
the MAC protocol. It offers a reasonable trade-
off between performance, robustness, and imple-
mentation costs. Using CSMA/CA, when a node
has a packet ready for transmission, it listens to
the channel. Once the channel has been detect-
ed as free (i.e., the energy level on the channel
is lower than the clear channel assessment, CCA,
threshold), the node starts the backoff procedure
by selecting a random initial value for the backoff
counter. The node then starts decreasing the back-
off counter while sensing the channel. Whenever a
transmission, either from other nodes within the
same WLAN or belonging to other WLANs, is
detected on the channel, the backoff counter is
paused until the channel is detected to be free
again, at which point the countdown is resumed.
When the backoff counter reaches zero, the node
starts transmitting. Figure 1a shows an example of
CSMA/CA operation.
dense WLAn scenArIos
Providing high data rates in scenarios where
the density of WLAN users is very high (e.g., 1
user/m
2
) requires the deployment of many APs
Boris Bellalta
IEEE 802.11ax: HIgH-EffIcIEncy WLans
a c c E p t E d f r o m o p E n c a L L
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