Ad-hoc Wireless Networks (AWN)

Introduction

In recent years mostly due to the growing prevalence of mobile computing devices, the popularity of wireless networking technology has increased dramatically,. Due to its convenience, wireless networking is becoming more popular in traditional desktop computers as well. Increasing trend is in the near future most computing devices will come with some form of wireless technology.
There are many situations which static infrastructure is either inconvenient or impractical, but nonetheless communication is desired. Users with mobile computers might want to collaborate on a group project in an outdoor area where there are no wireless access points. Or, users in a neighborhood might want to share a doc through the network, but without having to pay for broadband Internet access. Lastly the disaster scenarios are where the infrastructure may have been destroyed. Then the communication without infrastructure would be the desired solution. If the users of wireless networking devices wish to communicate with other networked devices, typically a static infrastructure such as a wireless access point or base station must be set up ahead of time to provide the wireless devices with connectivity. In these cases, the wireless devices can arrange themselves into an Ad Hoc network.
An Ad Hoc network is a collection of wireless nodes that form a network without the use of any static infrastructure such as a wireless Access Point. Instead of communicating via a centralized access point, the nodes in the network cooperate to allow information to be exchanged between them. In particular, each node acts as a router, forwarding packets for other nodes in the network.
The IEEE 802.11 specification uses the term Ad Hoc to describe a network composed solely of stations within mutual communication range of each other" [1]. In some cases Ad Hoc refers to multi-hop self-configuring wireless networks. Wikipedia define this as “A wireless ad hoc network is a decentralized wireless network”.

1. Ad-hoc Wireless network technologies
Most of the wireless network technologies are supported to create Ad-hoc networks while implementing those technologies in to practical situations. Some of those technologies are;

• Infrared
• Bluetooth
• WiFi
• WiMax
• WiBro

1.1 Infrared
Recently, it becomes popular to use small size computers such as notebook computers or PDAs in the mobile environment. It sometimes happens that several computers meet at the same place such as meeting rooms or conference sites. In such environment, there are demands to make a direct communication among mobile computers. Route maintenance and host enumeration are key requirement for such an ad hoc network.
Infrared technology allows computing devices to communicate via short-range wireless signals. With infrared, computers can transfer files and other digital data bidirectionally. The infrared transmission technology used in computers is similar to that used in consumer product remote control units. Infrared communications span very short distances. Place two infrared devices within a few feet (no more than 5 meters) of each other when networking them. Unlike Wi-Fi and Bluetooth technologies, infrared network signals cannot penetrate walls or other obstructions and work only in the direct "line of sight."

1.2 Bluetooth
Bluetooth uses radio waves to transmit wireless data over short distances. Bluetooth can support many users in any environment. Eight devices can communicate with each other in a small network known as piconet and it create small ad-hoc network here. At one time, ten of these piconets can coexist in the same coverage range of the Bluetooth radio and then it becomes a large ad-hoc network. A Bluetooth device can act both as a client and a server. A connection must be established to exchange data between any two Bluetooth devices. In order to establish a connection a device must request a connection with the other device. Bluetooth was based on the idea of advancing wireless interactions with various electronic devices. Devices like mobile phones, personal digital assistants, and laptops with the right chips could all communicate wirelessly with each other. However, later it was realized that a lot more is possible [15].

1.3 WiFi
Wi-Fi is the wireless technology to handle the networking/communication. Wi-Fi allocates internet connection globally and to be transmitted by the radio waves. Radio waves are the main cause of Wi-Fi. Radio waves are transmitted from antenna and Wi-Fi receivers pick them up. When a user receives the Wi-Fi signals, a wireless internet connection is produced and a user is prompted to provide the user name and password if required to establish a wireless connection.
Wi-Fi maintains certain security issues. WEP or Wired Equivalent Privacy is used in the physical and data link layers. It was planned to provide the wireless security by protecting the data, while it transmits from one point to another. Wi-Fi networking usually maintained inside a building premises. The data transmission in the Wi-Fi is protected by Wireless LANs but due to the fact that data travels over the radio waves so there are chance that data can be exposed and capture.

1.4 WiMax
WiMax is a wireless digital communications system, also known as IEEE 802.16, that is intended for wireless "metropolitan area networks". WiMax can provide broadband wireless access up to 30 miles for fixed stations, and 5 - 15 km for mobile stations. WiMax can be used for wireless networking in much the same way as the more common WiFi protocol. WiMax is a second-generation protocol that allows for more efficient bandwidth use, interference avoidance, and is intended to allow higher data rates over longer distances.

1.5 WiBro
Developed in South Korea, WiBro (Wireless Broadband) is the newest variety of mobile wireless broadband access. WiBro is based on the same IEEE 802.16 standard as WiMax, but is designed to maintain connectivity on the go, tracking a receiver at speeds of up to 37 miles per hour (60 km/h). WiMax is the current standard in the United States, offering wireless Internet connectivity to mobile users at fixed ranges of up to 31 miles (50 km) from the transmitting base. However, WiMax is not designed to be used while the receiver is in motion. WiBro can be thought of "mobile WiMax," though the technology and its exact specifications will change as it undergoes refinements throughout its preliminary stages.

2. Ad Hoc Routing Protocols
A number of different routing protocols have been proposed and evaluated in various work. We have mentioned a few of these protocols here.

• Dynamic Destination-Sequenced Distance-Vector (DSDV)
• Ad-hoc On-Demand Distance Vector (AODV)
• Dynamic Source Routing (DSR)
• Grid routing protocol

Most of the Ad-hoc routing protocols use hops count as their link metric when choosing routes in the network. That is, if a node has two candidate routes that it can use to send packets to a particular destination, it will always choose the route with the smallest number of hops.

2.1 Dynamic Destination Sequenced Distance (DSDV)
Dynamic Destination-Sequenced Distance-Vector (DSDV) routing protocol [2]. As its name suggests, DSDV is a distance vector routing protocol and operates by having each node in the network maintain a table of destination nodes along with a first hop and distance for each destination. Route updates are tagged with sequence numbers to avoid routing loop problems, and routing updates are broadcast on a periodic basis whether routing changes have occurred or not.

2.2 Ad-hoc On-Demand Distance Vector (AODV)
The Ad-hoc On-Demand Distance Vector (AODV) routing protocol [3] is similar to DSDV, but does not broadcast route updates periodically. Instead, routes are updated on an as-needed basis and each node only maintains entries in its routing table for nodes that it is actually communicating with. This reduces the amount of network traffic required for routing updates, and also reduces the complexity of routing information stored per node.

2.3 Dynamic Source Routing (DSR)
The Dynamic Source Routing (DSR) [4] protocol is somewhat similar to AODV in that it also avoids periodic routing updates. However, as its name implies, it uses source routing rather than distance vector routing, and the protocol authors claim that DSR responds more quickly to routing changes than do the distance vector protocols.

2.4 Grid Routing Protocol
The Grid routing protocol [5] is a position-based protocol. With this protocol, each node must know its own geographic coordinates, via GPS or some other mechanism. To send a packet to a particular destination, a node looks up the position of the destination node and forwards the packet to whichever of its neighbors is geographically nearest to the final destination. The Grid protocol includes a lookup service that allows nodes to learn the positions of other nodes in a scalable way.

3. Wireless Network Projects
3.1 Monarch Project Testbed
A testbed network originally developed at CMU as part of the Monarch project [10, 11] shares some of the goals of the Grid Roofnet, in particular the goal of providing an outdoor physical testbed for evaluating the performance and properties of Ad Hoc networking protocols. However, the Grid Roofnet has a number of major differences both in its goals and implementation. The Monarch testbed used mobile nodes mounted on cars to evaluate the performance of the DSR [13] protocol under dynamic network topologies. This differs from the Roofnet's static node locations, and goal of providing usable Internet access to users in a neighborhood. Probably the most signiffcant difference between this testbed and the Grid Roofnet is the wireless networking hardware used, which operated in the 900 Mhz range rather than the 2.4 Ghz range used by the Roofnet. Also, radios using the 802.11 standard were unavailable when the Monarch testbed was being built, and as a result their radios did not use 802.11. This probably turned out to be rather fortuitous for their system, as we have found the 802.11 layer to be less than ideal for building a multi-hop wireless network.

3.2 Nokia Rooftop
The Nokia Rooftop [6] is a commercial system capable of providing wireless broadband Internet access to residential areas. This is a commercial system and not a research platform. The Nokia system uses a variety of specialized proprietary hardware and methods in order to make their system perform well. Nokia Rooftop uses proprietary 2.4 GHz wireless routers. These routers use frequency-hopping radios which operate at variable power levels between 16 mw and 500 mw, which at the high end is five times the power output of the 802.11b radios used in the Grid Roofnet. The Nokia Rooftop uses a proprietary routing protocol. This protocol uses super nodes referred to as “Air Head routers" to route traffic between the mesh network and the Internet. The system is structured to have in most cases no more than two hops from a regular node to a super node. The routing protocol uses a common radio channel to cooperatively schedule non-interfering data burst transmissions between pairs of nodes and uses multiple data channels simultaneously to maximize overall network throughput. The system uses these multiple channels along with dynamic power control to avoid unnecessary interference between transmissions.

3.3 Ricochet MCDN
The Ricochet Micro Cellular Data Network (MCDN) System [7] is a commercial network providing Internet access to mobile users. The system provides Internet service via a network architecture in which end users use a radio modem which communicates with microcells. Packets from the user then pass from microcell to microcell until they reach a wired backbone, at which point the packets are routed to the Internet. The system uses proprietary routing algorithms to route packets from the microcells to the wired backbone and back, and has special provisions to ensure that nodes that are moving continue to stay in touch with microcells that are in radio range.
Although the Grid Roofnet and MCDN both share the very general goal of providing Internet access to end users via a multi-hop wireless network, the specific goals and implementation of the MCDN system differ significantly from the Grid Roofnet.

3.4 WINGS and DAWN
The Wireless Internet Gateways (WINGS) [8] and the Density and Asymmetry adaptive Wireless Network (DAWN) [9] projects are both part of the DARPA Global Mobile (GloMo) Information Systems program. Both address a number of issues in wireless networking, but in general tackle problems more related to mobility and military goals. The WINGS project extends the Internet to multi-hop wireless networks using an extension to the IP routing protocol. WINGS use a MAC layer protocol called FAMA-NCS that is somewhat similar to 802.11. A network layer protocol called WIRP (Wireless Internet Routing Protocol) that uses Dijkstra's shortest-path algorithm over a hierarchical graph of the network is used for packet routing. The WINGS project uses 900 MHz radios which are not 802.11. The goal of the DAWN project is to provide topologies for multi-hop wireless networks which have a number of properties that are of particular importance in tactical military networks.

3.5 Community Wireless Networking
In recent years a large number of non-profit community wireless networking projects have sprung up around the world. The goals of these projects vary, but generally include sharing Internet access in communities, providing free Internet access in public areas, and providing alternative networks that can be used to share information outside of the Internet. In the simplest cases they may consist simply of a number of individual users who have 802.11 access points connected to an Internet connection and share their connection freely, while some more ambitious projects are working to create metropolitan area wireless networks intended to augment the Internet.