Wireless ad hoc network
A wireless ad hoc network or mobile ad hoc network is a decentralized type of wireless network. The network is ad hoc because it does not rely on a pre-existing infrastructure, such as routers or wireless access points. Instead, each node participates in routing by forwarding data for other nodes. The determination of which nodes forward data is made dynamically on the basis of network connectivity and the routing algorithm in use.
Such wireless networks lack the complexities of infrastructure setup and administration, enabling devices to create and join networks "on the fly".
Each device in a MANET is free to move independently in any direction, and will therefore change its links to other devices frequently. Each must forward traffic unrelated to its own use, and therefore be a router. The primary challenge in building a MANET is equipping each device to continuously maintain the information required to properly route traffic. This becomes harder as the scale of the MANET increases due to the desire to route packets to/through every other node, the percentage of overhead traffic needed to maintain real-time routing status, all must share limited communication bandwidth, such as a slice of radio spectrum.
Such networks may operate by themselves or may be connected to the larger Internet. They may contain one or multiple and different transceivers between nodes. This results in a highly dynamic, autonomous topology. MANETs usually have a routable networking environment on top of a link layer ad hoc network.
History
Packet radio
The earliest wireless data network was called PRNET, the packet radio network, and was sponsored by Defense Advanced Research Projects Agency in the early 1970s. Bolt, Beranek and Newman Inc. and SRI International designed, built, and experimented with these earliest systems. Experimenters included Robert Kahn, Jerry Burchfiel, and Ray Tomlinson. Similar experiments took place in the amateur radio community with the x25 protocol. These early packet radio systems predated the Internet, and indeed were part of the motivation of the original Internet Protocol suite. Later DARPA experiments included the Survivable Radio Network project, which took place in the 1980s. A successor to these systems was fielded in the mid-1990s for the US Army, and later other nations, as the Near-term digital radio.Another third wave of academic and research activity started in the mid-1990s with the advent of inexpensive 802.11 radio cards for personal computers. Current wireless ad hoc networks are designed primarily for military utility. Problems with packet radios are: bulky elements, slow data rate, unable to maintain links if mobility is high. The project did not proceed much further until the early 1990s when wireless ad hoc networks were born.
Early work on MANET
The growth of laptops and 802.11/Wi-Fi wireless networking have made MANETs a popular research topic since the mid-1990s. Many academic papers evaluate protocols and their abilities, assuming varying degrees of mobility within a bounded space, usually with all nodes within a few hops of each other. Different protocols are then evaluated based on measures such as the packet drop rate, the overhead introduced by the routing protocol, end-to-end packet delays, network throughput, ability to scale, etc.In the early 1990s, Charles Perkins from SUN Microsystems USA, and Chai Keong Toh from Cambridge University separately started to work on a different Internet, that of a wireless ad hoc network. Perkins was working on the dynamic addressing issues. Toh worked on a new routing protocol, which was known as ABR – associativity-based routing. Perkins eventually proposed DSDV – Destination Sequence Distance Vector routing, which was based on distributed distance vector routing. Toh's proposal was an on-demand based routing, i.e. routes are discovered on-the-fly in real-time as and when needed. ABR was submitted to IETF as RFCs. ABR was implemented successfully into Linux OS on Lucent WaveLAN 802.11a enabled laptops and a practical ad hoc mobile network was therefore proven to be possible in 1999. Another routing protocol known as AODV was subsequently introduced and later proven and implemented in 2005. In 2007, David Johnson and Dave Maltz proposed DSR – Dynamic Source Routing.
Applications
The decentralized nature of wireless ad hoc networks makes them suitable for a variety of applications where central nodes can't be relied on and may improve the scalability of networks compared to wireless managed networks, though theoretical and practical limits to the overall capacity of such networks have been identified.Minimal configuration and quick deployment make ad hoc networks suitable for emergency situations like natural disasters or military conflicts. The presence of dynamic and adaptive routing protocols enables ad hoc networks to be formed quickly.
Mobile ad hoc networks (MANETs)
A mobile ad hoc network is a continuously self-configuring, self-organizing, infrastructure-less network of mobile devices connected without wires. It is sometimes known as "on-the-fly" networks or "spontaneous networks".Vehicular ad hoc networks (VANETs)
s are used for communication between vehicles and roadside equipment. Intelligent vehicular ad hoc networks are a kind of artificial intelligence that helps vehicles to behave in intelligent manners during vehicle-to-vehicle collisions, accidents. Vehicles are using radio waves to communicate with each other, creating communication networks instantly on-the-fly while vehicles move along roads. VANET needs to be secured with lightweight protocols.Smartphone ad hoc networks (SPANs)
A SPAN leverages existing hardware and software in commercially available smartphones to create peer-to-peer networks without relying on cellular carrier networks, wireless access points, or traditional network infrastructure. SPANs differ from traditional hub and spoke networks, such as Wi-Fi Direct, in that they support multi-hop relays and there is no notion of a group leader so peers can join and leave at will without destroying the network. Apple's iPhone with iOS version 7.0 and higher is capable of multi-peer ad hoc mesh networking.Wireless mesh networks
Mesh networks take their name from the topology of the resultant network. In a fully connected mesh, each node is connected to every other node, forming a "mesh". A partial mesh, by contrast, has a topology in which some nodes are not connected to others, although this term is seldom in use. Wireless ad hoc networks can take the form of a mesh networks or others. A wireless ad hoc network does not have fixed topology, and its connectivity among nodes is totally dependent on the behavior of the devices, their mobility patterns, distance with each other, etc. Hence, wireless mesh networks are a particular type of wireless ad hoc networks, with special emphasis on the resultant network topology. While some wireless mesh networks have relatively infrequent mobility and thus infrequent link breaks, other more mobile mesh networks require frequent routing adjustments to account for lost links.Army tactical MANETs
Military or tactical MANETs are used by military units with emphasis on data rate, real-time requirement, fast re-routing during mobility, data security, radio range, and integration with existing systems. Common radio waveforms include the US Army's JTRS SRW, Silvus Technologies MN-MIMO Waveform, and Codan DTC MeshUltra Waveform. Ad hoc mobile communications come in well to fulfill this need, especially its infrastructureless nature, fast deployment, and operation. Military MANETs are used by military units with an emphasis on rapid deployment, infrastructureless, all-wireless networks, robustness, security, range, and instant operation.Air Force UAV ad hoc networks
Flying ad hoc networks are composed of unmanned aerial vehicles, allowing great mobility and providing connectivity to remote areas.Unmanned aerial vehicle, is an aircraft with no pilot on board. UAVs can be remotely controlled or can fly autonomously based on pre-programmed flight plans. Civilian usage of UAV include modeling 3D terrains, package delivery, etc.
UAVs have also been used by US Air Force for data collection and
situation sensing, without risking the pilot in a foreign unfriendly environment.
With wireless ad hoc network technology embedded into the UAVs, multiple UAVs can communicate with each other and work as a team, collaboratively to complete a task and mission. If a UAV is destroyed by an enemy, its data can be quickly offloaded wirelessly to other neighboring UAVs.
The UAV ad hoc communication network is also sometimes referred to UAV instant sky network. More generally, aerial MANET in UAVs are now successfully implemented and operational as mini tactical reconnaissance ISR UAVs like the BRAMOR C4EYE from Slovenia.
Navy ad hoc networks
Navy ships traditionally use satellite communications and other maritime radios to communicate with each other or with ground station back on land. However, such communications are restricted by delays and limited bandwidth. Wireless ad hoc networks enable ship-area-networks to be formed while at sea, enabling high-speed wireless communications among ships, enhancing their sharing of imaging and multimedia data, and better co-ordination in battlefield operations.Some defense companies have produced products that enhance ship-to-ship and ship-to-shore communications.