IEEE 802.

11 WLAN TECHNOLOGY
The Wireless Local Area Network (WLAN) aims to provide wireless data connectivity
within a smaller area such as a building, or an office/college campus. WLANs have gained
immense popularity and are now available on most laptops and several high-end PDAs. The
low cost, ease of installation, and almost no maintenance requirement has resulted in several
businesses looking at the WLAN as a convenient corporate solution. WLAN technology offers
many unique features such as license-free 2.4 GHz ISM band operation, omnidirectional robust
transmission with low radiations, simplified spontaneous operation without much complicated
setup requirements, plug-and-play basis, simple to use operation, in-built encryption
mechanisms, maintaining user privacy, support for location aware applications, and battery-
operated low-power devices.
Compared with wired LAN, WLAN operates in a hostile wireless medium for communication
with an additional requirement to support mobility and security. The wireless medium has
serious bandwidth limitations, frequency regulations, location- and time- dependent multipath
fading, and interference from other WLANs or wireless devices operating in its near vicinity.
Moreover, WLANs are not restricted to any physical boundaries, and they overlap with each
other. The 802.11 standard needs to examine management of connection, link reliability,
power, and link security. The IEEE standard 802.11 specifies a family of WLANs which define
the detailed specifications of physical and MAC layers to accommodate any connectionless
data-oriented networks for wireless wideband local access.

WLAN Advantages and Disadvantages

There are a number of advantages of wireless LAN over wired LAN, which are
summarised as below:
 Quicker Deployment: Adding new subscribers to existing WLAN facility does not involve
making physical connections or running cables or patching new jacks.
 LAN Extension: The WLAN can provide services to inaccessible areas by extending the
wired LAN Internet connectivity. Thus, it is economical in situations where the site is not
conducive to LAN wiring because of building or budget limitations, such as older buildings,
leased space, or temporary locations.
 Easy Access: To hook up to the existing network, the user just needs to enable the wireless
device to access the available WLAN services as per the network configuration. There is no
need of connecting any cable or finding the plug.
 WLAN Mobility: The WLAN mobile users can access the network from anywhere within
the radio coverage area of the network at any time. There is no line-of-sight requirement
with the wireless access points till the received signal strength is good as the radio waves
can penetrate the obstacles. For example, students attending class on a campus access the
Internet or exchange information for learning.
 Cost Effective: After the initial cost of installation and commissioning of the network, there
is no extra cost incurred in the infrastructure for providing services to additional WLAN
users. Wireless technology saves a lot of expenses on cabling, labour, and maintenance.
Most WLAN devices are equipped with plug-and-play feature. This helps to reduce the cost
 due to vendor technical installation, equipment maintenance and to eliminate equipment
redundancy in case of system crash.
 Smart Working: Senior executives or managers can present their briefings using WLAN,
without carrying the data files, charts, and any other storage material. The ad-hoc network
can be configured for peer-to-peer communication.
 Increased Productivity: Wireless technologies have a direct impact on real-time increase
in productivity due to minimum set-up requirements with centralised database access.

There are certain disadvantages of wireless LAN such as the following:

 Limited Bandwidth: Due to limited bandwidth and data-rate capability, the WLAN
technology cannot support video teleconference or real-time applications. The WLAN is not
capable to download and upload large data files quickly.
 Incompatibility: WLAN devices from different manufacturers are often incompatible with
each other as well as with other networks due to usage of a number of different standards.
The problem has been the lack of interoperability among WLAN products from different
manufacturers.
 Interference and Loss of Signal: The wireless link is not always reliable due to external
noise and interference. The received signal strength may vary significantly, resulting in
sudden disconnections or heavy errors. Also, there is interference to other wireless networks
operating in the near vicinity.
 Black or Dead Spots: Due to the type of surrounding structure (steel reinforcing materials)
or high-power running machinery, there may be some spots where there is zero or very weak
radio signal strength, thereby rendering the services inaccessible.
 Less Security: Due to insecure wireless medium, the network is more vulnerable for
malicious attacks and jamming.
 Need of Backbone Network: Wireless transmission is slower, less efficient and less reliable
compared to wired networks. The operation of WLAN is dependent on the reliable wired
backbone network.

IEEE 802.11 System Architecture

The IEEE 802.11 WLAN standard could be used to provide communication between a
number of subscriber terminals as a client/server wireless configuration in infrastructure mode,
or as an ad-hoc network using peer-to-peer mode, or a fairly complicated distributed network.
The IEEE 802.11 standard defines two basic modes of system architectures to provide
connectivity to wireless terminals:
 An infrastructural mode, where a number of wireless terminals are either configured as a
client/ server mode via a wireless LAN Access Point (AP), or as a distributed wireless
network connected to a wired LAN via a number of access points that acts as gateways
between the wireless terminals and the wired network. In this mode of operation, the number
of wireless terminals are connected to a backbone network through wireless access points.
 An infrastructure-less ad-hoc mode, where wireless terminals do not require the presence
of an access point, and form a network by directly communicating, and co-coordinating,
 with each other to exchange information through the system. In the ad-hoc system
architecture mode, wireless terminals communicate in a peer-to-peer basis.

The key components for all these system architectures are wireless Network Interface Cards
(Wireless NIC) installed within wireless terminals and WLAN access points. Each access point
has a radio coverage area, that is, a limited range of operation, which is typically 200–500
metres in an open environment. The AP is usually placed high on the side walls on the interiors
of a building or at the ceiling of a room/corridor and supports a large number of (usually, 115
to 250) wireless-terminal users transmitting, receiving, and buffering data between the WLAN
and the wired network. Wireless terminals operating within an access point’s coverage area are
capable of receiving signals from that access point.

Infrastructural mode
In the client/server configuration, many wireless terminals such as laptops equipped with
wireless interface cards are physically close to each other, typically 20 to 500 metres. They can
be linked to a common AP which functions as a central hub that serves as a bridge between
them and the existing wired LAN. The wireless access cards installed as an add-on unit with
the wireless terminals provide the interface between the PCs and the antenna, while the AP
serves as the WLAN hub.

Figure below illustrates the infrastructure-based WLAN system architecture as client/server

wireless configuration.

Figure given below illustrates the infrastructure-based WLAN system architecture as a

distributed wireless network configuration.
 As indicated in the figure, an access point may be implemented as part of a wireless
terminal. In fact, the AP may be a logic within a wireless terminal that provides access to the
DS by enabling DS services in addition to acting as a wireless terminal. The AP provides access
to a Distribution System (DS) through the wireless medium to a number of wireless terminals
located within the radio coverage of the AP. It is essential that all participating wireless
terminals must execute the same MAC protocol and compete for access to the same shared
wireless medium using CSMA/CA protocol. The access-point, together with the wireless
terminals associated with it operating within its radio coverage, form a Basic Service Set
(BSS). In a BSS, wireless terminals do not communicate directly with one another. If one
wireless terminal in the BSS wants to establish communication with another wireless terminal
in the same BSS, the MAC frame is first sent from the calling wireless terminal to the AP, and
then from the AP to the called wireless terminal. Thus, the AP can be thought of functioning
as a relay point, and a BSS can be referred as a cell. Thus, the two wireless terminals that are
communicating within the same BSS get the call routing service from the single AP of that
BSS.

To integrate the IEEE 802.11 architecture with a traditional wired LAN, a portal is
deployed. The portal logic is implemented in a device such as a bridge or router, which is a
part of the wired LAN and attached to the Distribution System (DS). A BSS is also connected
to a backbone DS through an access point. The DS can be a switch, a bridged IEEE wired LAN,
or another wireless network. Typically, the DS is a wired backbone LAN but can be any
communication network. A distribution system connects several BSSs via the AP to form a
single network and thereby extends the wireless coverage area. In other words, the collection
of BSSs connected by a wired network (also called a distribution system) is known as an
Extended Service Set (ESS). The distribution system connects the wireless networks via the
APs with a portal, which forms the interworking unit to other LANs. Thus, an ESS consists of
two or more basic service sets interconnected by a distribution system. The ESS has its own
unique identifier termed as the ESSID. The ESS appears as a single logical LAN to the logical
link control layer.
If a wireless terminal in one BSS wants to establish communication with another
wireless terminal located in a different BSS, the MAC frame containing the ESSID is first sent
from the calling wireless terminal to the AP of its home BSS, and then relayed by the AP over
the DS on its way to the destination BSS and then finally called to remote wireless terminal via
its AP. Thus, the AP can be thought of functioning as a bridge as well as a relay point, and an
ESS can be referred as a cellular network. The ESSID is used to identify different networks
and may be referred as the name of a network itself. Without knowing the ESSID, the wireless
terminals cannot participate in the WLAN.

Ad-hoc WLAN System Architecture In addition to infrastructure-based networks, the IEEE

802.11 standard allows the system architecture of ad-hoc networks among wireless terminals,
thus forming one or more Independent BSSs (IBSS) as shown

In an ad-hoc WLAN system architecture, an IBSS comprises of a group of wireless

terminals either using the same carrier transmission frequency without any overlapping of their
respective radio coverage areas, or using the different carrier transmission frequencies allowing
overlapping of their respective radio-coverage areas. For example, the wireless terminal WT1,
WT2, and WT3 are configured within their respective radio-coverage areas forming IBSS1.
Similarly, WT4 and WT5 forms IBSS2. This means that WT1 can communicate directly with
WT3, but not with WT5 because there is no AP or DS which can connect both IBSSs. As there
is no central controller in the ad-hoc architecture, the wireless access cards use the CSMAS/CA
protocol to resolve shared access of the wireless medium.

IEEE 802.11 Standards

The IEEE 802.11 is the dominant family of standards for WLAN in the world. The IEEE 802.11
specifies physical layer and MAC layer standards, operating at the 2.4 GHz ISM band with a
data rate of 1 or 2 Mbps, protocols, power levels, modulation schemes, and so on. The MAC
layer should be able to operate with multiple physical layers, each of which exhibits a different
medium sense and transmission characteristic such as infra-red and spread spectrum radio
transmission techniques.
IEEE 802.11a WLAN Standards
802.11a was published in 1999 as a modification to 802.11, with orthogonal frequency division
multiplexing (OFDM) based air interface in physical layer instead of FHSS or DSSS of 802.11.
It provides a maximum data rate of 54 Mbps operating in the 5 GHz band. Besides it provides
error correcting code. As 2.4 GHz band is crowded, relatively sparsely used 5 GHz imparts
additional advantage to 802.11a. The IEEE 802.11a uses the US 5 GHz UNII (Unlicensed
National Information Infrastructure) frequency band. The UNII band is divided into three parts:
(a) The UNII-1 Band 5.15 GHz to 5.25 GHz with maximum power output 50 mW for indoor
applications
(b) The UNII-2 Band 5.25 GHz to 5.35 GHz with maximum power output 250 mW either
indoor or outdoor applications
(c) The UNII-3 Band 5.725 GHz to 5.825 GHz with maximum power output 1W for outdoor
applications
The IEEE 802.11a standard specifies Orthogonal Frequency Division Multiplexing
(OFDM), also called multicarrier modulation as baseband modulation scheme. OFDM uses
multiple carrier signals at different frequencies, transmitting some of the bits on each channel.
All the subchannels are dedicated to a single data source. The IEEE 802.11a specifications
supports the use of various coding and carrier modulation schemes. A convolution code at a
rate of 1/2, 2/3, ¾ or provides forward error correction. The system uses up to 48 subcarriers
with frequency spacing of 0.3125 MHz that are modulated using BPSK, QPSK, 16-QAM, or
64-QAM digital modulation schemes.

IEEE 802.11b WLAN Standards

In order to meet the user demand for higher data rates, the IEEE standard 802.11b (popularly
known as Wi-Fi for Wireless Fidelity), is an extension of the IEEE 802.11 DSSS standards and
specifies a physical layer providing a basic rate of 11 Mbps and a fall-back rate of 5.5 Mbps in
the 2.4 GHz ISM band. The chipping rate is 11 Mcps and provides the same occupied
bandwidth as that of original IEEE 802.11. In order to achieve a higher data rate in the same
bandwidth in the same chipping rate, the IEEE 802.11b standard specifies the use of a
modulation scheme known as Complementary Code Keying (CCK) is used. The system uses
CSMA/CA technique, and the typical coverage is up to 100 metres. The security level is
comparatively low.

IEEE 802.11g WLAN Standards

The IEEE 802.11g WLAN standard operates at 2.4 GHz ISM band with new modulation
schemes, forward error correction and OFDM scheme to provide a wider array of data rates
from 1 Mbps to 54 Mbps. IEEE 802.11g is backward compatible with 802.11 and 802.11b
standards by specifying the same modulation and framing schemes for 1, 2, 5.5, and 11 Mbps
data rates. IEEE 802.11g adopts the 802.11a OFDM scheme for 6, 9, 12, 18, 24, 36, 48, and 54
Mbps. The OFDM scheme is referred to as Extended Rate Physical (ERP) layer OFDM. In
addition, ERP Packet Binary Convolutional Coding (ERPPBCC) scheme is used to provide
data rates of 22 and 33 Mbps optionally
IEEE 802.11n WLAN Standards

The IEEE 802.11n WLAN standards provides a series of enhancement techniques to both the
physical layer and MAC layers leading throughput of up to 100 Mbps. The standards include
Multiple-Input Multiple-Output (MIMO) and 40-MHz operation to the physical layer. The
standard includes the use of multiple antennas, smart antennas, change of signal encoding
schemes and MAC access protocols. It addresses other performance-related requirements such
as more uniform radio coverage, improved range at existing throughputs, and increased
resistance to interference

IEEE 802.11ac WLAN Standards

IEEE 802.11ac-2013 is an amendment to IEEE 802.11, published in December 2013, that

builds on 802.11n. The standard has been retroactively labelled as Wi-Fi 5. Changes compared
to 802.11n include wider channels (80 or 160 MHz versus 40 MHz) in the 5 GHz band, more
spatial streams (up to eight versus four), higher-order modulation (up to 256-QAM vs. 64-
QAM), and the addition of Multi-user MIMO (MU-MIMO).

IEEE 802.11ax WLAN Standards

Wi-Fi 6 (802.11ax) technology is all about better and more efficient use of the existing radio
frequency medium. Higher data rates and wider channels are not the goals of Wi-Fi 6. The goal
is better and more efficient 802.11 traffic management. Most of the Wi-Fi 6 enhancements are
at the PHY layer and involve a new multi-user version of OFDM technology instead of the
single-user OFDM technology already used by 802.11a/g/n radios. Another significant Wi-Fi
6 change is that an access point (AP) can supervise both downlink and uplink transmissions to
multiple client radios while the AP controls the medium. In addition to these multi-user
efficiency enhancements, Wi-Fi 6 (802.11ax) radios will be backward compatible with
802.11/a/b/g/n/ac radios. Unlike 802.11ac radios, which can transmit only on the 5 GHz
frequency band, 802.11ax radios can operate on both the 2.4 GHz and 5 GHz frequency bands.

WLAN Applications
Wireless LANs have clear-cut edge over traditional wired LANs because WLANs satisfy the
additional requirements for mobility, ad-hoc networking, relocation, and coverage of locations
which are difficult to wire. Due to advancements in transmission technologies, modulation and
coding techniques, and many new protocols and algorithms, WLANs have been able to achieve
acceptable data rates, reasonable security, and occupational safety concerns in an unlicensed
worldwide frequency band. One of the major application areas for WLAN lies in its capability
either to provide similar services as an alternative to a wired LAN where laying of cables is not
feasible, or as an extension to existing wired LAN to new operational areas. Thus, a wireless
LAN offers an effective solution to set up either a peer-to-peer ad-hoc network with no
centralised server or an infrastructure network to link with wired LAN and servers.
The WLAN must meet certain requirements such as connectivity among hundreds of wireless
terminals across multiple BSSs as well as to fixed terminals on a wired backbone LAN,
broadcast capability, hand-off/roaming capability, transmission robustness, data security,
collocated WLANs operation, dynamic configuration, low power consumption, and so on.
Wireless LANs allow for the design of small, independent and battery-operated devices such
as small PDAs and notepads. They can survive natural disasters, and wireless communication
can still be established if the wireless devices are safe. After providing wireless access to the
infrastructure via an access point for the first wireless terminal, addition of more wireless
terminals in WLANs does not require any change in fixed infrastructure and hence are cost
effective.
There are still few challenges and issues which need to be addressed for enhancement of
application areas. For example, WLANs typically offer limited data rate with lower quality of
service than their wired LANs. This is mainly because of lower bandwidth availability in radio
transmissions. WLANs can offer only 1–10 Mbps data rate instead of 100–1,000 Mbps for
wired LANs, higher error rates (10−4 instead of 10−12 for fiber optics) due to interference,
eavesdropping, unwanted radiations, and longer delay due to usage of extensive error
correction and detection mechanisms in WLANs. Moreover, WLANs are limited to operation
in license-free frequency bands, which are not the same worldwide.

HIPERLAN TECHNOLOGY
High Performance Radio LAN (HIPERLAN) is a pan-European alternative for the IEEE
802.11 WLAN standards, and is defined by the European Telecommunications Standards
Institute (ETSI). In ETSI, the HIPERLAN standards are defined by the Broadband Radio
Access Networks (BRAN) project. The HIPERLAN standards provide features and capabilities
similar to those of the IEEE 802.11 WLAN standards, used in the US and other adopting
countries.
The HIPERLAN standard family has four different versions: HiperLAN/1, HiperLAN/2,
HIPERACCESS, and HIPERLINK.
 The high-speed HiperLAN/1 standard supports mobility at data rates above 20 Mbps in
the 5-GHz RF band up to 100-m radio range. It specifies both infrastructure and multi-
point to multi-point ad-hoc system architecture.

 HiperLAN/2 operates at up to 54 Mbps in the same RF band up to 25 Mbps data rates

in an ad-hoc system architecture, and has the potential for sending and receiving data,
images, and voice communications, and intends to accommodate ATM as well as IP-
type access with QoS support.

 HIPERACCESS technology is used for remote access up to 5 km, up to 25 Mbps data

rates, having provision for more than 155 Mbps with QoS.
  HIPERLINK is designed to interconnect different access points and switches with a
high-speed link in the backbone of up to 155 Mbps data-rate capability.

The specific requirements for HIPERLAN can be listed as

– Multi-hop and ad hoc networking capability
– Radio coverage up to 100 metres
– Support of both asynchronous and synchronous traffic
– Data rates up to 23.5 Mbps in the 5.2 GHz unlicensed band
– Support of time-bounded services and power-saving mode
The maximum data rate for the user depends on the distance of the communicating nodes. With
short distances up to 50 m and asynchronous transmission, a data rate of 20 Mbps is achieved;
with up to 800-m distance, a data rate of 1 Mbps are provided. For connection-oriented services
such as video-telephony, data rates of at least 64 kbps are offered.

HIPERLAN/1 System Architecture

HIPERLAN/1 is mainly designed to work without the need of any infrastructure. Two nodes
may exchange data directly, without any interaction from a wired (or radio-based)
infrastructure. Thus, the simplest HIPERLAN/1 consists of two nodes. Further, if two
HIPERLAN/1 nodes are not in radio contact with each other, they may use a third node which
must forward messages between the two communicating nodes. Figure shows the overall
system architecture of an ad-hoc HIPERLAN/1.

A multihub topology is considered that also allows overlay of two HIPERLANs to extend the
communication beyond the radio range of a single node. There are two overlapping
HIPERLANs, A and B, and the node 4 acts as a bridge between the two. Each node is
designated either as a Forwarder (F) node or a Non-Forwarder (NF) node. In the above figure,
nodes 1, 4, and 6 are forwarder nodes and these have forwarding connections. A forwarder
node retransmits the received packet to other nodes in its neighbourhood, if the packet is not
meant for it. Nodes 2, 3, and 5 are non-forwarder nodes, which simply accept the packet that
is meant for it. Each non-forwarder node should select at least one of its neighbour nodes as a
forwarder node. Inter- HIPERLAN forwarding needs mutual agreement and cooperation, and
should exchange regular update messages to support proper routing and maintenance.
HIPERLAN/2 Standards
HIPERLAN/2 is designed as a fast wireless connection for many kinds of networks such as the
UMTS backbone network, ATM and IP networks. HIPERLAN/2 allows interconnection into
almost any type of fixed network technology. This makes it suitable, for example, to connect
mobiles, portables and laptops to a fixed access point. The basic services provided in
HIPERLAN/2 are QoS in voice, data, and video transmission. HIPERLAN/2 also provides
unicast, multicast and broadcast transmissions.
It uses the unlicensed 5 GHz U-NII band and supports up to 54 Mbps data rate at the physical
layer and about 35 Mbps at the network layer. Modulation techniques such as BPSK, QPSK,
16QAM or 64QAM are used. The physical layer of HIPERLAN/2 is very similar to IEEE
802.11a wireless LANs. However, the multiple access technique is dynamic TDMA in contrast
to CSMA/ CA used in IEEE 802.11a.

IEEE 802.15 WPAN TECHNOLOGY

The IEEE 802.15 standards is a family of protocols to address the needs of Wireless Personal
Area Network (WPAN) at different data rates in 2.4 GHz ISM band, same as defined in IEEE
802.11 WLAN standards. A WPAN is a wireless communications network among a number
of portable and mobile devices on the network such as cellphones, pagers, PCs, laptops,
peripherals, PDAs, and consumer electronic devices within a small service area of up to about
10 metres, which enables the use of low power, low cost, and extremely small-sized devices.

IEEE 802.15.1 System Architecture

The IEEE 802.15.1 WPAN standards support applications which require medium data rate
(typically up to 1 Mbps). Bluetooth technology has been adopted as the IEEE 802.15.1 WPAN
standards which are commercially available in numerous devices ranging from cellphones,
PDAs, laptops to wireless mouses and cameras. Bluetooth devices can communicate with other
Bluetooth devices in several ways. The basic unit of the WPAN system architecture is a
piconet. It consists of a master device and from a minimum of one to a maximum of seven
slave devices. All slave devices must be within 10-metre radio range of the master device. The
master device determines the assignment of frequency- hopping sequence and timing offset for
slave devices to transmit. A slave device may only communicate with the master device after
getting permission to do so. There can be 255 parked slave devices in the single piconet but at
any time, a maximum of seven are communicating.

Figure depicts a simple configuration of a piconet architecture.

Each of the slave devices has an assigned 3-bit active device address. Many other inactive slave
devices can remain synchronised to the master device, referred to as parked devices. The master
device regulates the channel access and other operations for all active devices as well as parked
devices. Piconet supports both point-to-point and point-to-multipoint connections.

A device in one piconet may also exist as part of another piconet and may function as either a
master or slave in each piconet. This form of system architecture configured from overlapping
piconets is called a scatternet. Thus, a scatternet can be referred to a group of independent and
non-synchronised piconets that share at least one common device. The objective to form
scatternets is to provide effective and efficient communication over multiple hops with
acceptable response times and power consumption so that end-to-end wireless communication
links can be established.

All communication between devices takes place between a master and a slave, using time-
division duplex, with no direct slave-to-slave communication. The master will poll each active
slave to determine if it has data to transmit. The slave may only transmit data when it has been
polled. Also, it must send its data in the time slot immediately following the one in which it
was polled. The master transmits only in even-numbered time slots, while the slaves transmit
only in odd-numbered time slots. In each time slot, a different frequency channel is used (a hop
in the hopping sequence).
A piconet is established with a potential master device identifying other devices in its radio
coverage area that wish to participate in the piconet. It begins with an INQUIRY message by
the potential master device if the address is unknown, followed by a subsequent PAGE
message. If the address is already known, a connection is made by sending a PAGE message
only.

IEEE 802.15.1 Protocol Architecture

The IEEE 802.15 WPAN standard protocol architecture defines the physical layer
specifications and MAC layer requirements. The IEEE 802.15.1 standards, also popularly
known as Bluetooth specifications, defines the physical layer comprising of a Frequency-
Hopping Spread Spectrum (FHSS) device that uses the worldwide unlicensed 2.4-GHz ISM
frequency band. In most countries including US, there are 79 different frequency channels
available in the available 2.4 GHz–2.4835GHz ISM band. The nominal bandwidth for each
channel is 1 MHz. A Bluetooth transceiver uses all 79 channels, and hops (changes frequencies)
pseudo randomly across all channels at a rate of 1600 hops per second for data transmissions.
When connected to other Bluetooth devices, a Bluetooth device hops in a pseudorandom
sequence, with each physical channel occupied for 625 μs. Each 625 μs time period is referred
to one time slot, and these are numbered sequentially.
The Bluetooth specification uses Time Division Duplexing (TDD) and Time Division Multiple
Access (TDMA) for device communication. TDD is a link transmission technique in which
data are transmitted in one direction at a time, with transmission alternating between uplink
and downlink directions. Since more than two devices share the piconet medium, the access
technique can be characterised as FH-TDD-TDMA.

IEEE 802.15.3 High-Rate WPAN

The IEEE 802.15.3 standard, also called WiMedia, physical layer operates in the unlicensed
2.402–2.480 GHz frequency band. It is designed to achieve higher data rates of the order of
11–55 Mbps, which are needed in high-fidelity audio and high-definition video applications.
WiMedia Ultra Wideband (UWB) technology is optimised for Wireless Personal-Area
Networks (WPANs), delivering high-speed, low-power multimedia capabilities for the PC,
mobile and automobile market segments The IEEE 802.15.3 standard defines the specifications
for high-rate WPANs supporting speeds of 11 Mbps, 22 Mbps, 33 Mbps, 44 Mbps, and up to
55 Mbps in the 2.4 GHz ISM band. It supports peer-to-peer or adhoc networks. It supports two
different channel plans––a coexistence channel plan, and a high-density channel plan. It uses
Trellis Code Modulation (TCM) and Forward Error Correction (FEC) technique which encodes
the digital signal so that single bit errors can be detected and corrected.

UWB transmits low-power, short-range signals. UWB broadcasts a very short digital pulse
(less than 1 ns) that is timed very precisely. The sender and receiver must be synchronised with
very high accuracy. If the sender knows exactly when a pulse should arrive, multi-path
propagation is no longer an issue because only the strongest signal will be detected within a
very short time slot. UWB technology can be used for WLANs transmitting very high data
rates over short distances. UWB can send data at speeds of up to 2 Gbps. The IEEE 802.15.3
system employs a 11 Mbps symbol rate, and uses Trellis-coded QPSK at 11 Mbps, uncoded
QPSK modulation at 22 Mbps, and 16/32/64-QAM at 33, 44, 55 Mbps respectively.

IEEE 802.15.4 Low-Rate WPAN

The IEEE 802.15.4 standards define low-rate, low-power WPANs with low bandwidth
requirements. The physical layer specifies the operation at 2.4-GHz ISM band worldwide to
offer a transmission data rate of 250 kbps. It supports 16 channels between 2.4 GHz and 2.4835
GHz with a 5-MHz channel spacing. It employs a 16-ary quasi-orthogonal modulation
technique based on DSSS binary data which offers better performance than differential BPSK.
The applications have few or no QoS requirements with provision for retransmission of data in
case of errors due to interference. Moreover, transmissions will be infrequent, with the devices
operating in a passive mode most of the time. Higher throughput, lower duty cycle, and lower
latencies are the features of these specifications.

Comparison of IEEE 802.15 WPAN standards

WPAN Applications

(a) A Wireless Personal Area Network (WPAN), popularly known as Bluetooth technology, is
an extremely short-range wireless network, formed around the personal operating space of a
wireless terminal with built-in Bluetooth device.
(b) Typically, WPANs are used to replace cables between a computer and its peripheral
devices.
(c) WPANs can be used for transmitting images, digitised music, and other data.
(d) Bluetooth is the only WPAN technology which is commercially available and is an essential
component in a series of devices ranging from laptops to wireless mouses to cameras and
cellphones.
(e) Bluetooth technology enables short-range wireless communication networks between user
devices incorporating a Bluetooth interface, and greatly improves the way users access services
and data wirelessly.
(f ) With the help of Bluetooth technology, ad-hoc wireless piconets can be formed, which are
local area networks with a very limited coverage (about 10 metres) and without the need for an
infrastructure, offering asynchronous data and synchronous voice services at data rate of 1
Mbps.
(g) Mobile phones could have a built-in Bluetooth chip in place of WLAN adapters. The mobile
phone can then act as a bridge between the local piconet and the cellular network. In this way
a mobile phone can be connected to a PDA or laptop in a simple way using wireless piconets.
(h) Bluetooth standard utilises a short-range radio link to exchange information, enabling
effortless wireless connectivity between mobile phones, mobile laptops, handheld computers
and other peripherals.
(i) Bluetooth technology aims to replace the IrDA specifications of Infrared in mobile phones
and computing devices.
(j) Bluetooth can connect cellular mobile phones, a laptop, notebooks, desktop PCs, PDAs,
handsfree headsets, LCD projectors, printers, modems, wireless LAN devices, FAX machines,
keyboards, joysticks, and virtually any other digital device to one another via Bluetooth short-
range radio modules installed in each of these devices, replacing the cable used to connect
them.
(k) Bluetooth also provides a universal bridge to existing data networks and a mechanism to
form small private Mobile Ad-hoc Networks (MANETs).
(l) WPANs help in the interworking of wireless technologies to create heterogeneous wireless
networks. For instance, WPANs and WLANs will enable an extension of devices without direct
cellular access to 3G cellular systems.
(m) Devices interconnected in a WPAN should be able to utilise a combination of both 3G
access and WLAN by selecting the access mechanism that is best suited at a given time. In
such networks, 3G, WLAN, and WPAN technologies do not compete against each other but
enable the user to select the best connectivity for intended purposes. Facts to Know !
(n) The Bluetooth specification defines two transmit power levels––a low transmit-power level
that covers a small personal area within a room, and a high transmit-power level that can cover
a medium range, such as an area within a home or office.

IEEE 802.16 WMAN TECHNOLOGY

The IEEE 802.16 standards address the needs of Wireless Metropolitan Area Network
(WMAN) that can provide data communication network in an entire city. The access to the
data network is provided by the WMAN to buildings through exterior antennas, communicating
with base stations. It can also extend the capabilities of existing cabled access networks such
as coaxial systems using cable modems, DSL links, and fiber optic links. The IEEE 802.16
standards have been evolved as a set of air interfaces at 10 GHz–66 GHz band on a common
MAC protocol layer. The IEEE 802.16a, also known as WiMAX, extends the air interface
support to lower frequencies in the licensed as well as unlicensed 2 GHz–11 GHz band. The
WiMAX system can serve more wireless terminal users at relatively lower data rates.

Need of Wireless MAN

In general, wireless networks allow users to be connected as they move about, freeing them
from cumbersome wires/cables and phone lines. WLANs and WPANs have restricted both
connections and mobility, allowing users to roam around a few hundreds of metres from the
source of the RF signal. These users have also been restricted mostly to stay within line-of-
sight antennas. Therefore, user mobility has remained largely confined to offices, homes, and
hotspots (such as airports and some public places in larger cities) except for voice
communications and low-speed data over cellular networks. WMANs are a group of
technologies that provide wireless connectivity across a substantial geographical area such as
a large metropolitan city.
IEEE 802.16 Protocol Architecture
The IEEE 802.16 standard specifies the physical layer in the 10 GHz–66 GHz band. The
channel bandwidths are typically 20 MHz and 25 MHz in US, and 28 MHz in Europe. The
point-to-point wireless communication is enabled through a TDM scheme in which a base
station transmits the data sequentially to each wireless terminal in its allocated time slot in the
downlink direction. The channel access in the uplink direction is by TDMA technique.
For the deployment of single-carrier transmission the line-of-sight conditions must exist. The
burst design selected allows coexistence of both FDD (full-duplex as well as half-duplex) and
TDD forms of communication. The FEC encoded data is mapped to a QPSK, 16-QAM or 64-
QAM to form burst transmissions with varying efficiency and robustness.

The IEEE 802.16 MAC layer protocol supports point-to-multipoint broadband wireless access.
It accommodates both continuous and burst type of data traffic.

IEEE 802.16a WiMAX

WiMAX is an acronym that stands for Worldwide Interoperability for Microwave Access.
WiMAX, also known as Wireless Metropolitan Area Networks (WMANs), provides
broadband wireless connectivity across a substantial geographical area such as a large
metropolitan city. It is based on the IEEE 802.16a standard and has been designed to evolve as
a set of air interfaces based on a common MAC protocol but with physical layer specifications
having an air interface support in the 2–11 GHz band, including both licensed and license-
exempt spectra.
WiMAX can use radio channel bandwidths that can vary from 1.25 MHz to 28 MHz in steps
of 1.75 MHz in 2 GHz–11 GHz band, and uses multicarrier OFDMA scheme to achieve
transmission data rates as high as 155 Mbps. WiMAX can provide multiple types of services
to the same user with different Quality of Service (QoS) levels. For example, it is possible to
install a single WiMAX transceiver in an office building and provide real-time telephone
services and best effort Internet browsing services on the same WiMAX connection
The maximum distances achievable in a WiMAX network depend on the frequency band used.
Higher frequencies are used for metropolitan area line-of-sight, point-to-point, or multipoint
applications at very high data rates. Lower licensed frequencies will be used for private, line-
of-sight network connections of up to 16 kilometers and long-distance links of up to 56
kilometres. Frequencies below 11 GHz will be used for non-line-of-sight networks with a
maximum range of up to 8 kilometres. In a typical cell radius deployment of 3-10 kilometres,
WiMAX systems can be expected to deliver capacity of up to 40 Mbps per channel.

WiMAX and LTE/3GPP – Comparison

The two prominent mobile broadband technologies are 3G/3G+ cellular and WiMAX
technologies. 3G cellular mobile technologies, as defined by IMT2000, are Wideband Code
Division Multiple Access (WCDMA), also known as Universal Mobile Telecommunications
System (UMTS) in Europe, and Code Division Multiple Access 2000 (Cdma2000). WCDMA
is a technology with backward compatibility with GSM, while Cdma2000 is an advanced
technology of CdmaOne. WCDMA uses Direct Sequence Spread Spectrum (DSSS) to spread
the baseband signal over a 5 MHz spectrum. It is based on the Third Generation Partnership
Project (3GPP) Release 99 and provides data rates of 384 kbps for wide area coverage and up
to 2 Mbps for hotspot areas. The improvements in WCDMA for data capabilities came in the
form of High Speed Packet Access (HSPA) technologies which improved the data speeds of
up to 14.4 Mbps for downlinks and 5.76 Mbps for uplinks. Cdma2000 evolutions for data
handling capabilities have came in the form of Cdma2000 1x, 1x- EV-DV (Evolutionary Data
and Voice), 1x EV-DO (Evolutionary Data Only) and Cdma2000 3x (also called IMT-2000
CDMA MC). It can provide the speed of around 2–4 Mbps and use Orthogonal Frequency
Division Multiple Access (OFDMA) technology. The IMT-2000 family of standards support
four different multiple access technologies, including FDMA, TDMA, CDMA, and OFDMA
(includes WiMAX).
Technological advancements in the form of 3.5G, Long Term Evolution (LTE) or Super 3G
and Ultra Mobile Broadband (UMB) are also under consideration in order to meet the demands
of increasing data rate applications and value-added services such as interactive video.
The prominent features of LTE include
– High data rates of up to 100 Mbps for downlinks and 50 Mbps for uplinks
– Data-centric networks instead of voice-centric networks
– Use of advanced OFDMA technology instead of CDMA
– Horizontally oriented structure instead of vertically oriented
– Flexibility for operators to deploy in different-sized bands according to availability of
spectrum
– Higher spectral efficiencies by using advanced antenna systems like MIMO (Multi-Input
Multi-Output)

LTE defines new radio connections for mobile networks, and will utilise Orthogonal Frequency
Division Multiplexing (OFDM), a widely used modulation technique that is the basis for Wi-
Fi, WiMAX, and the DVB and DAB digital broadcasting technologies as well.

The key features of WiMAX technology include

– Advanced performance (high per-user throughput and low latency)
– Wide variety of devices (laptop add-in cards and modules, game consoles)
– IP-based, optimised for packet-based data applications
– Support for IMS (Internet Multimedia Subsystems)
– Next-generation multiplexing technique
– Support for advanced antenna techniques/systems like MIMO (Multi-Input Multi-Output)
and beam forming
– Multiple hand-off mechanisms (supports a variety of hand-off mechanisms)
– Worldwide availability (operates in three spectrum bands: 2.3–2.4 GHz, 2.496–2.69 GHz and
3.4–3.6 GHz)
– Dynamic bandwidth allocation (enabling flexible management of spectrum resources and a
more efficient use of spectrum)
– Easy integration with technologies like 2G, 3G and Wi-Fi
– Tolerance to multi-path and self-Interference
– Global roaming (allows subscribers to access different networks using the same device and
a single, familiar interface)Facts to Know !
– Equipment based on open standards, an attractive Intellectual Property Rights (IPR)
structure and high base-station capacity