IEEE 802.11
IEEE 802.11 defines the set of
standards for local area network, personal area network or other area network protocols. It also specifics the MAC and PHY
layer protocols for wireless local area network commonly known as Wi-Fi. It
operates over a large number of frequencies bands such as 2.4 GHz, 5 GHz, 6 GHz
and 60 GHz etc. maintained by the institute of electrical and electronics
engineers (IEEE) LAN/MAN standard committee (IEEE 802).
General Features:
The 802.11 family uses half-duplex
over-the-air modulation techniques and employs carrier sense multiple access
with collision avoidance (CSMA/CA). The 802.11 families work over the different
frequency bands and use different modulation and optimization techniques. For
example, 802.11b and 802.11g use the 2.4 GHz ISM band, and most commonly found
in an application such as and 802.11 g uses the 2.4 GHz ISM band with only
three non-overlapped 20 MHZ wide channel. We usually found equipment using
these standard band in devices such as microwave ovens, cordless telephones and
Bluetooth devices. 802.11b and 802.11g uses direct sequence spread spectrum
(DSSS) and orthogonal frequency division multiplexing (OFDM) signaling methods
respectively for controlling and susceptibility the interference. 802.11a uses
the 5 GHz band and has at least 23 non-overlapped 20 MHz wide channel.
802.11n can use either the 2.4 GHz or 5
GHz band. Best or worse performance with the higher or lower frequency channels
may be realized and usually depends on the environment where we are using.
Higher frequency has higher bandwidth or speed but has low range whereas lower
frequency has lower bandwidth or speed but has a higher range.
The segment of the radio frequency
spectrum used by 802.11 varies between countries.
Is Wi-Fi and IEEE 802.11 same?
IEEE 802.11 is a
set of technical guidelines that describes procedures, limits, values,
algorithms to establish a LAN/WLAN connection.
IEEE 802.11 main role is developing technical specifications for WLAN implementation however interconnection between vendors cannot be achieved even meeting the IEEE 802.11 standards. Therefore, Wi-Fi Alliance group was formed to resolve the issue.
Fig. 1: Relationship between IEEE 802.11 and Wi-Fi Alliance.
Wi-Fi is a brand
name owned by the Wi-Fi Alliance that certifies with pre-defined tests the
interoperability between the operating devices. Wi-Fi devices are based on IEEE
802.11.
IEEE
802.15:
IEEE standards committee specifies IEEE
802.15 as wireless personal area network (WPAN) standards.
802.15.1 defines
physical layer (PHY) and Media Access Control (MAC) specification
for wireless connectivity with fixed, portable, and moving
devices within or entering personal operating space.
It is also commonly known as Bluetooth
technology standards. These networks are designed for inexpensively connecting low-power
devices located within 1 m to 100 m of each other. The Bluetooth,
802.15.4/Zigbee and Ultra-Wideband fall under IEEE 802.15 standards.
The first, Bluetooth, is deployed in
hundreds of millions of mobile or equipment of daily use. It offers higher data
rates of upto 3Mbps and with up to a range of 100 m, with far lower power
consumption than 802.11b.
Its middleware layer builds on top of
Physical (PHY) and medium access control (MAC) layers to provide a high degree
of interoperability.
The low power consumption and interoperability
guarantee have made use of Bluetooth's features in the mobile phone community.
Bluetooth devices are divided into one
of three classes according to the antenna's output power. Class 1 devices
broadcast using 1 mW to 100 mW power. Class 2 devices broadcast using 0.25 mW
to 2.5 mW power. Class 3 devices broadcast using up to 1 mW power. Bluetooth
devices form networks either piconets or scatternets. Piconets consist of one
master device that communicates directly with up to 7 active slave devices.
Piconets can also have up to 250 parked (i.e., inactive) slave nodes at any
given time. Multiple piconets can also be combined into a single multi-hop
scatternet.
Communication within a piconet occurs
directly between a master and a slave, however, slaves cannot communicate
directly. Bluetooth uses a basic time-division duplexing (TDD) scheme, where
time is divided into 625 μs slots. The master may communicate with a slave
during the odd-numbered slots, and slaves respond during the even-numbered
slots. Each packet may consume 1, 3, or 5 slots. After each packet, the piconet
hops to a different Bluetooth channel; the next channel's frequency is
determined using a pseudo-random number generator.
The second of these technologies,
802.15.4 (Zigbee), provides even higher data rates and speed than Bluetooth.
Zigbee offers data rates of up to 250 kbps, and can easily support links with a
very low duty cycle. Hence, it is suitable for deployment in battery-powered
devices that must survive for up to a year between charges. Zigbee has already
found wide acceptance in the wireless sensor network community, but research is
going on using of Zigbee in-home applications.
ZigBee specifies the three different
device types: Coordinator, router, and end devices and work either in full
function device or reduce function device mode. Coordinators are 802.15.4 fully
function devices (FFDs) that act as 802.15.4 coordinator nodes and maintain
ZigBee-specific information about the PAN (master encryption keys, etc.). Routers
are 802.15.4 FFDs that participate in ZigBee's routing protocols. End devices are
analogous to 802.15.4's reduced function devices (RFDs). RFDs must communicate
with each other by way of an intermediary coordinator or router.
Finally, ultra-wideband (UWB) radios
provide low-power, high-bandwidth pulses that deliver data rates comparable to
wired Ethernet. Its high data rates and relatively low power consumption make
it ideal for replacing short wired links, PC peripherals, and in-home theatres.
UWB uses short pulses (in the
picosecond to nanosecond range) over a large bandwidth (often many GHz). It
offers very high data rates (Mbps or in Gbps) with relatively low power
consumption. The use of short pulses over a wide spectrum also means that the
signal is below the average power output defined as noise by the FCC (-41.3
dBm/MHz), and that UWB signals are not susceptible to noise or jamming.
Unfortunately, IEEE standardization of
UWB has failed, resulting in two incompatible standards: DS-UWB, advocated by
the UWB Forum; and MB-OFDM, advocated by the Wi-Media Alliance. Like Zigbee,
UWB is still in its first stages of deployment, making it difficult to predict
its future success.
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