electronica Nov 2014
38
W
IRELESS
Five trends shaping 802.11 WLANs
By Amal Ekbal,
National Instruments
This article describes
in detail five specific trends
which will likely shape the growth
of WiFi technology in the future.
Although these are the
five biggest trends today,
the progression of technology has
a way of surprising everyone.
Wireless local area networks (WLANs)
based on WiFi technology have become
a standard part of life for many, whether
integrated within a home television or a
radio-controlled drone helicopter. The latest
commercially available version of WiFi, based
on the Institute of Electrical and Electronics
Engineers (IEEE) 802.11ac standard, provides
significant connectivity improvements. In
addition, it is driving upgrades in consumer
and enterprise markets from earlier versions,
such as IEEE 802.11n. As the use of WLANs
has grown, so have feature requests, helping to
drive the evolution of WiFi more rapidly than
ever. The WiFi brand name popularized by the
WiFi Alliance refers to products based on the
IEEE 802.11 family of WLAN standards. The
IEEE 802.11 standard was first approved in
1997. Subsequent amendments added inno-
vations such as orthogonal frequency division
multiplexing (OFDM; from IEEE 802.11a)
and multiple-input, multiple-output (MIMO)
antenna systems (from IEEE 802.11n) to keep
up with market requirements.
As table 1 shows, the theoretical peak phys-
ical layer (PHY) data rate supported by
the standard has increased by more than
100× over the past decade: from 54 Mb/s in
IEEE 802.11g to 6.9 Gb/s in IEEE 802.11ac.
Although these PHY rates do not directly
translate to data throughput due to channel
access and protocol overheads, improvements
in the IEEE 802.11 medium access control
(MAC) layer (such as packet aggregation and
block acknowledgments) enable present-day
IEEE 802.11 devices to achieve 70% to 80%
efficiency. Improvements in data rate are
not the only trend in WiFi evolution. What
follows is a review of five important trends
expected to shape the WiFi ecosystem over
the next decade.
The first trend involves the market rollout of
products based on the IEEE 802.11ac wireless
standard. The current wave of IEEE 802.11ac
products is part of release 1, which added
support for wider 80-MHz bandwidth with
as many as three MIMO spatial streams, per-
frame dynamic bandwidth selection, and high-
er-order modulation operation, in the form
of 256-point quadrature amplitude modula-
tion (256 QAM). In addition, IEEE 802.11ac
simplifies and improves a number of features
present in IEEE 802.11n, such as transmit
beam forming. Based on a 3×3 MIMO con-
figuration with 80-MHz bandwidth, the pres-
ent-day typical release 1 IEEE 802.11ac access
point supports a peak PHY data rate of 1.3
Gb/s. Release 2 devices for IEEE 802.11ac
are anticipated to support even wider band-
width (160 MHz) operation and four MIMO
spatial streams. Release 2 is also likely to sup-
port downlink (DL) multi-user (MU) MIMO
(DL MU-MIMO). As illustrated in figure 1,
today a WiFi access point can only support
one client at a time using single-user MIMO
(SU-MIMO) operation. Since devices such as
laptop computers and smartphones usually
support only one or two antennas and most
IEEE 802.11ac access points support three or
four antennas, this leads to a waste of MIMO
resources and lower throughput. MU-MIMO,
also shown in figure 1, allows the access
point to use spatial separation to send data
to multiple clients at the same time and fully
utilize its MIMO capabilities. MU-MIMO
in IEEE 802.11ac is limited to the downlink
direction - i.e. for data packets sent from the
access point. MU-MIMO has the potential to
increase network capacity since it minimizes
packet collisions, reduces network usage, and
reduces interference to neighboring networks.
Note, however, that performance improve-
ments due to MU-MIMO can vary drastically
depending upon the spatial distribution of
devices and data traffic patterns.
The second trend in WiFi is the development
of high-efficiency WLANs. WiFi has become
so ubiquitous that it is being deployed in
dense,
high-interference
environments,
such as airports and office buildings. Use in
such environments usually results in low-
er-than-expected data rates and sluggish
performance. For example, WiFi users may
