Ad hoc Networks
requisite Discussion :
In this chapter we present several
wireless local area network (WLAN) technologies. This constitutes a
fast-growing market introducing the flexibility of wireless access into office,
home, or production environments. WLANs are typically restricted in their
diameter to buildings, a campus, single rooms etc. and are operated by
individuals, not by large-scale network providers The global goal of WLANs is
to replace office cabling, to enable tether less access to the internet and, to
introduce a higher flexibility for ad-hoc communication in, e.g., group
meetings. The following points illustrate some general advantages and
disadvantages of WLANs compared to their wired counterparts.
1.Wireless LAN :
Some advantage of WLAN (or)
Characteristics of WLAN
Within radio coverage, nodes can
communicate without further restriction. Radio waves can penetrate walls,
senders and receivers can be placed anywhere. Sometimes wiring is difficult if
firewalls separate buildings. Penetration of a firewalls is only permitted at
certain points to prevent fire from spreading too fast.
Only wireless ad-hoc networks allow
for communication without previous planning any wired network needs wiring
plans. As long as devices follow the same standard they can communicate. For
wired networks, additional cabling with the right plug and probably
interworking units such as switches have to be provided
Wireless networks allow for the
design of small, independent devices which can for example be put into a
pocket. Cables not only restrict users but also designers of small PDAs,
notepads etc. Wireless senders and receivers can be hidden in historic
buildings. i.e., current networking technology can be introduced without being
Wireless networks can survive
disasters e.g., earthquakes or user pulling a plug. If the wireless devices
survive people can still communicate. Networks requiring a wired infrastructure
will usually break down completely.
After providing wireless access to
the infrastructure via an access point for the first user, adding, additional
users to a wireless network will not increase the cost.
This helps to know the characteristics and
features of using Wireless LAN
2. IEEE 802.11
The three main sections of this chapter present
the IEEE standard for WLANs, IEEE 802.11, the European ETSI standard for a
high-speed WLAN with QoS support
3. SYSTEM ARCHITECTURE
Wireless networks can exhibit two different
Several nodes called stations (STA)
STA are connected to access points (AP) stations (or) terminals with access mechanisms to the wireless medium and radio contact to the AP.
BSS (Basic Service Set)
A Group of stations using the same radio
The example two BSSs (i.e.) BSS1 and BSS2 -
which are connected via a distribution system.
A distribution system connects several BSSs via
the AP to form a single network and thereby extends the wireless coverage area.
Interconnection network to form one logical
network (ESS :- Extended Service Set) based on several BSS.
Extended service set (ESS) has its own
identifier, the ESSID.
The ESSID is the name of a network and is used to separate different networks. Without knowing the ESSID it should not be possible to participate in the WLAN.
Bridge to other wired networks.
The distribution system connects the wireless
networks via the APs with a portal which forms the interworking unit to other LANs.
Stations can select an AP and associate with
The APs support roaming ie. Changing access
distribution system handles data transfer between the different APs.
within a BSS
power management and
control medium access to support time bounded service
5. Mobile Ad hoc Networks Concept:
An ad-hoc network is a local area network (LAN)
that is built spontaneously as devices connect. Instead of relying on a base
station to coordinate the flow of messages to each node in the network, the
individual network nodes forward packets to and from each other. In Latin, ad
hoc literally means "for this," meaning
"for this special purpose" and also, by extension, improvised or
The Ad Hoc Networks is an international and
archival journal providing a publication vehicle for complete coverage of all
topics of interest to those involved in ad hoc and sensor networking areas. The
Ad Hoc Networks considers original, high quality and unpublished contributions
addressing all aspects of ad hoc and
sensor networks. Specific areas of interest include, but are not limited to:
and Wireless Ad Hoc Networks
Local and Personal Area Networks
Hoc Networks of Autonomous Intelligent Systems
Architectures for Ad Hoc and Sensor Networks
Network Architectures and Protocols
protocols (unicast, multicast, geocast, etc.)
Access Control Techniques
Low-Power and Energy-Efficient Designs
and Scheduling Issues
Tracking and Location-based Services
and Information Management
and Fault-Tolerance Issues
and Software Platforms, Systems, and Testbeds
and Prototype Results
Analysis and Simulation of Protocols
It is used for mobile nodes to
communicate without any infrastructure.
6. WIFI and WIMAX :
These are used for data transfer and
wireless communication such like Bluetooth, but it can connect devices in
higher range. WiMAX is similar to the wireless standard known as Wi-Fi, but on
a much larger scale and at faster speeds. A nomadic version would keep
WiMAX-enabled devices connected over large areas, much like today.s cell
phones. We can compare it with Wi-Fi based on the following factors.
Wi-Fi typically provides local
network access for around a few hundred feet with speeds of up to 54 Mbps, a
single WiMAX antenna is expected to have a range of up to 40 miles with speeds
of 70 Mbps or more. As such, WiMAX can bring the underlying Internet connection
needed to service localWi-Fi networks.
Wi-Fi is intended for LAN
applications, users scale from one to tens with one subscriber for each CPE
device. Fixed channel sizes (20MHz).
WiMAX is designed to efficiently
support from one to hundreds of Consumer premises equipments (CPE)s, with
unlimited subscribers behind each CPE. Flexible channel sizes from 1.5MHz to
Wi-Fi works at 2.7 bps/Hz and can
peak up to 54 Mbps in 20 MHz channel. WiMAX works at 5 bps/Hz and can peak up
to 100 Mbps in a 20 MHz channel.
Wi-Fi does not guarantee any QoS but
WiMax will provide your several level of QoS. As such, WiMAX can bring the
underlying Internet connection needed to service local Wi-Fi networks. Wi-Fi
does not provide ubiquitous broadband while WiMAX does.
Used real time in organizations and
used in smart phones.
7. Wireless Local Loop
The first step in the receiver
involves demodulating the received signal. This is achieved using the same
carrier as the transmitter reversing the modulation and results in a signal
with approximately the same bandwidth as the original spread spectrum signal.
Additional filtering can be applied to generate this signal. While demodulation
is well known from ordinary radio receivers, the next steps constitute a real
challenge for DSSS receivers, contributing to the complexity of the system. The
receiver has to know the original chipping sequence, i.e., the receiver
basically generates the same pseudo random sequence as the transmitter.
Sequences at the sender and receiver have to be precisely synchronized because
the receiver calculates the product of a chip with the incoming signal. This
comprises another XOR operation as explained in section 3.5, together with a
medium access mechanism that relies on this scheme. During a bit period, which
also has to be derived via synchronization, an integrator adds all these products. Calculating the products of
chips and signal, and adding the products in an integrator is also called correlation, the device a correlator. Finally, in each bit period a decision
unit samples the sums generated by the integrator
and decides if this sum represents a binary 1 or a 0. If transmitter and
receiver are perfectly synchronized and the signal is not too distorted by
noise or multi-path propagation,. On the receiver side, this signal is XORed bit-wise after demodulation with the
same Barker code as chipping sequence.
∑ Used to provide data coverage to a
small area with high speed with WiMax
∑ Provides an infrastructure for
establishing a mobile communication