22-12-2012, 02:51 PM
WIRELESS AD HOC NETWORK
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Abstract:
A wireless ad-hoc network is a decentralized wireless network that does not rely on a preexisting infrastructure. A principal property of wireless ad hoc networks is the use of wireless nodes to produce, consume, and relay data on a flexible, as-needed basis appropriate for the intended application. The research area of wireless ad-hoc networks now includes Mobile Ad-Hoc Networks (MANETs), Wireless Mesh Networks (WMNs), Vehicle Ad-Hoc Networks (VANETs), and Wireless Sensor Networks (WSNs), as well as innovative extensions in areas such as 3G and 4G cellular networks. Additionally, wireless ad-hoc networking and embedded computing and sensing are providing novel solutions to long-standing challenges in other application areas.
INTRODUCTION
There are two typical categories of wireless networks cellular (one hop) networks and wireless ad hoc (multi hop) networks. Wireless ad hoc networks (formerly called packet radio networks) are defined as mobile distributed multihop wireless networks. In a wireless ad hoc network, there is no predetermined topology (preexisting fixed infrastructure) and no central control. The nodes in ad hoc networks communicate without wired connections among themselves by creating
a network “on the fly”. Wireless ad hoc networks are traditionally used in
Battlefield communications, law enforcement, and disaster recovery (fire, earthquake, etc.), and emergency search and rescue
TYPES OD AD HOC NETWORK
Wireless Mesh network (WMN):
Wireless mesh networks can easily, effectively and wirelessly connect entire cities using inexpensive, existing technology.
In a wireless mesh network, the network connection is spread out among dozens or even hundreds of wireless mesh nodes that "talk" to each other to share the network connection across a large area.
Nodes are programmed with software that tells them how to interact within the larger network.
Information travels across the network from source to destination by hopping wirelessly from one mesh node to the next. The nodes automatically choose the quickest and safest path in a process known as dynamic routing.
Mesh nodes are small radio transmitters that function in the same way as a wireless router. Nodes use the common Wi-Fi standards known as 802.11(a, b, g) to communicate wirelessly with users, and, more importantly, with each other.
In a WMN, only one node needs to be physically wired to a network connection like a DSL Internet modem. That one wired node then shares its Internet connection wirelessly with all other nodes in its vicinity. Those nodes then share the connection wirelessly with the nodes closest to them. The more nodes, the further the connection spreads, creating a wireless "cloud of connectivity" that can serve a small office or a city of millions.
Mobile ad hoc networks (MANET):
A MANET is a self-configuring infrastructure less network of mobile devices connected by wireless.
Each device in a MANET is free to move independently in any direction, and will therefore change its links to other devices frequently.
The topology of the network (arrangement of the devices) changes dynamically with time.
VANET is one type of mobile ad-hoc nework.
A type of MANET that is fast gaining wide research focus. VANETs are used for communication among vehicles (equipped with wireless devices) and between vehicles and roadside equipment.
IP ROUTING PROTOCOLS
An Ad Hoc network (also called a Mobile Ad Hoc Network MANET) consists of wireless hosts that move around, i.e. they have no permanent physical location. In order to facilitate communication within the network, a routing protocol is used to discover routes between nodes before the exchange of
IP data packets. Below is a brief overview of IP routing in an Ad Hoc environment. There
The routing protocols in Ad Hoc wireless networks are generally categorized as:
1) Table driven routing protocol (Proactive):
These protocols require each node to maintain one or more tables to store up to date routing information and to propagate updates throughout the network. These protocols try and maintain valid routes to all communication mobile nodes all the time, which means before a route is actually needed. Periodic route updates are exchanged in order to synchronize the tables. It has to maintain O(N) state per node, N = #nodes.