Lou Frenzel, Contributing Editor
What’s the Difference
Between IEEE 802.11ah
and 802.11af in the IoT?
Looking to gain a foothold in the Internet of Things, HaLow and White-Fi bring low-
power and long-range potential to a wide array of applications.
T
he IEEE standard 802.11 usually defines what we 11af
Frequency Cellular
all know as Wi-Fi. Multiple versions of this stan- 54-698 MHz
600-900
dard exist, but not all are designated as Wi-Fi despite 11ah MHz
11 b/g/n 900 MHz
their being a part of the family. Specifically, consider
11a/ac 2.4 GHz
two relatively recent versions of the standard: 802.11af, now 11ad 5 GHz
referred to as White-Fi, and 802.11ah, otherwise known as 60 GHz
HaLow. Both versions, which are more suited to Internet of
Things (IoT) applications, offer benefits beyond traditional
Wi-Fi, including longer range and lower power consumption. Wireless
10 m 50 m 100 m
This article takes a closer look at these standards, either of node 1 km 1-3 km 3 km+
which could be the solution to your next design. Range
IoT Requirements These are the approximate maximum ranges of 802.11 wireless
Most IoT applications involve sensors transmitting minimal technologies. Environment, obstacles, etc. can shorten or lengthen
data from remote locations over short distances. A core these ranges.
requirement is low power consumption—most applications
are battery-operated, so long battery life is a must. with higher power up to the imposed FCC limits and by using
Another burgeoning need is longer range. Most IoT gain antennas.
applications cover short range from 10 to say 100 meters. Using a lower frequency also extends range. For the same
However, many others need to extend that range from 100 power, along with other factors, dropping the operating
meters to many kilometers. Low data rates (less than 1 Mb/s) frequency below 1 GHz will dramatically extend the useful
are typical. range. Another benefit of lower-frequency signals is that they
Traditional wireless technologies such as Wi-Fi, Bluetooth, penetrate buildings and other obstacles better than higher
ZigBee, and others can easily handle the short-range frequencies. In fact, non-line-of-sight (NLOS) operation is
applications, but their operating frequency limits that range. possible. The 802.11af and 802.11ah standards take advantage
Power consumption may be an issue, too. of the characteristics provided by these lower frequencies (<
The distance traveled by a radio wave of a given power, 1 GHz).
antenna gain, and receiver sensitivity directly relates to the
operating frequency. The physics of radio indicates that The Wi-Fi Option
the range is inversely related to frequency. In other words, If your application requires high data rates and the expected
lower-frequency signals naturally travel farther than higher- range is less than 100 meters, a conventional Wi-Fi radio may
frequency signals. be your best bet. Examples include video monitoring in the
Most of the basic short-range technologies operate in the home or some commercial/industrial use requiring internet
2.4-GHz band, or 5 GHz. However, range can be extended access and good security.
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The widely used 802.11n standard can produce speeds to Korea, 916-927 MHz in Japan, and 755-787 MHz in China.
300 Mb/s. The more recent 802.11ac operates in the 2.4- or This is good news because low power can be used over these
5-GHz bands and achieves speeds in excess of 1.3 Gb/s. The lower frequencies, enabling battery-operated equipment.
main limitations are a range of up to 100 meters, depending on While most Wi-Fi gear has a maximum range of 100 meters
the environment, and medium to high power consumption. under ideal conditions, HaLow can reach up to a kilometer
Higher data rate needs can be met, though, with the 802.11ad with the right antenna.
WiGig option operating at 60 GHz. Range is typically less The 902- to 928-MHz spectrum offers 26 MHz of bandwidth
than 10 meters, but speeds can reach up to 7 Gb/s. Other that’s divided into 1-, 2-, 4-, 6-, or 16-MHz channels. The
choices are available if you need longer range and lower power 11ah modulation scheme is orthogonal frequency-division
consumption. multiplexing (OFDM) using 24 subcarriers in a 1-MHz
The figure shows the estimated maximum ranges for the channel and 52 data subcarriers in the larger bandwidths.
802.11 standards. Keep in mind that the environment, terrain, Modulation can be BPSK, QPSK, or 16QAM, 64QAM, or
obstacles, and other factors either shorten or lengthen those 256QAM with multiple coding options, providing for a wide
approximations. range of data rates. Rates of 100 kb/s in a 1-MHz channel
and up to several hundred megabits per second in a 16-MHz
Long-Range, Low-Power Options channel are easily achieved.
If you’re looking for a long-range, low-power wireless The real goal of 11ah is low power. The typical user station
solution, lots of choices are available. Table 1 lists the primary has a sleep mode to conserve battery charge. Short data
alternatives for building a low-power wide area network packets and shortened contention access procedures minimize
(LPWAN) with extended range. Space doesn’t permit a transmit time and power usage.
comprehensive discussion of each, but more background The standard supports a massive number of possible
information is available in the article “Long-Range IoT on the network stations (8191). A special station type is the relay
Road to Success” on www.electronicdesign.com. access point, which helps all other stations pass along messages
The choices boil down into two groups: proprietary, non- over longer distances at low power.
standard technologies and cellular. Cellular is an interesting Support is also provided for up to four spatial data streams to
choice, as it provides excellent range and reliable coverage further boost data rate. In addition, the antenna-sectorization
with existing networks. The downsides for some applications feature partitions the coverage area.
are high cost and high power consumption. Proprietary The 802.11ah standard is blessed by the Wi-Fi Alliance
technologies cover many use cases, so some evaluation is (WFA), which gave it the trade name HaLow. The WFA says
needed. Then again, the IEEE standards may simply be the that it will implement one of its testing and certification
answer. programs for HaLow by 2018.
HaLow is a sophisticated technology that has yet to be
HaLow (802.11ah) widely adopted. Nevertheless, it’s still worthy of consideration
This standard can use any industrial-scientific-medical for new projects.
(ISM) frequency spectrum below 1 GHz, but the primary
targeted band is the 902- to 928-MHz license-free band in White-Fi (802.11af)
the U.S. Similar bands just below 1 GHz are found in other White Fi, also known as Super Wi-Fi, is designed to use the
countries, such as 863-868 MHz in Europe, 717-723 MHz in TV white spaces (TVWS) or the unused TV channels from 54
to 698 MHz. These channels are ideal
to support long-range and non-line-
MAIN FEATURES OF LPWAN TECHNOLOGIES of-sight transmission. The standard
Data rate employs cognitive-radio technology
Technology Frequency Range Power Cost
max and geolocation database access to
Ingenu 2.4 GHz 624 kb/s Many km Low Medium ensure that there’s no interference
LoRa 915 MHz <50 kb/s 15 km Low Low
to local TV signals or other services
operating in this region (e.g., wireless
LTE-M Cellular bands 1 Mb/s Several km Medium High
microphones). The base station queries
NB-IoT Cellular bands 250 kb/s Several km Medium High a database to see what channels are
Sigfox <1 GHz 100-1000 b/s Several km Low Medium available locally for data transmission.
Symphony 915 MHz <50 kb/s Up to 10 km Low Medium The 802.11af standard works with
Weightless <1 GHz 0.1-24 Mb/s Several km Low Low
TV channels that have bandwidths of
6, 7, or 8 MHz. Modulation is OFDM
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using BPSK, QPSK, 16QAM, 64QAM, or 256QAM. A wide
range of coding rates allow for optimization of the connection.
The maximum data rate per 6-MHz channel is about 24 Mb/s.
A typical mobile user station can have a transmit power of
100 mW, while a base station or access point has up to 4 W
of power.
Range depends on the actual frequency. Several kilometers
can be achieved at the higher frequencies. Even longer ranges
of up to several miles are possible at the lower VHF TV
frequencies.
This standard isn’t part of the Wi-Fi Alliance family, unlike
802.11ah. Its main competition is the Weightless group of
TVWS open standards and some proprietary designs. Few, if
any, actual operating networks have been implemented.
Technologies Looking for Adopters
Though both of these standards are viable options for
new IoT applications, activity with them hasn’t been visible.
For low-speed, long-range, and low-power use cases, both
technologies offer superior benefits. What’s hindered their
adoption is the fact that they joined the IoT movement late in
the game, and the competition is fierce.
The 11ah and 11af standards aren’t only battling the long-
range vendors listed in the table, but also some of the other
traditionally short-range wireless technologies that can offer
extended range in the popular 2.4-GHz band. One example
is 802.15.4-based technologies like ZigBee—a ZigBee
option offers 902- to 928-MHz operation. Newer versions of
Bluetooth may be another longer-range option, depending
pon the environment and equipment.
As you pursue new IoT or M2M projects, keep your mind
open to 11ah and 11af as possible solutions.
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