Ad Hoc Network Ammar Abu-Hudrouss Islamic University Gaza ١ Introduction An ad hoc wireless network is a collection of wireless mobile nodes that self-configure to form a network without the aid of any established infrastructure. Webster s lists two relevant definitions for ad hoc: formed or used for specific or immediate problems, and fashioned from whatever is immediately available. They avoid the cost, installation, and maintenance of network infrastructure. They can be rapidly deployed and reconfigured. They also exhibit great robustness due to their distributed nature, node redundancy, and the lack of single points-of-failure. Technology is not mature yet! Research opportunities. Slide 2 ١
Applications The lack of infrastructure is highly desirable for low-cost commercial and for military systems. If the network is designed for maximum flexibility to support many applications then it will be difficult to tailor the network to different application requirements. This will likely result in poor performance for some applications, especially those with high rate requirements or stringent delay constraints. On the other hand, if the network is tailored to a few specific applications then designers must predict in advance what these killer applications will be - a risky proposition. Slide 3 Data Netwroks Ad-hoc wireless data networks primarily support data exchange between laptops, palmtops, personal digital assistants (PDAs), and other information devices. These data networks generally fall into three categories based on their coverage area: LANs, MANs, and WANs. Infrastructure-based wireless LANs are already quite prevalent, and deliver good performance at low cost. The advantages of Ad-Hoc networks lies on : First, only one access point is needed to connect to the backbone wired infrastructure: this reduces cost and installation requirements Slide 4 ٢
In addition, it can be inefficient for nodes to go through an access point or base station. For example, PDAs that are next to each other can exchange information directly rather than routing through an intermediate node.. The challenge in these networks is to support high data rates, in a cost-effective manner, over multiple hops, where the link quality of each hop is different and changes with time. Ad-Hoc Networks may be dropped into remote areas where network infrastructure cannot be developed. In addition, networks that must be built up and torn down quickly, e.g. for military applications or disaster relief, are infeasible without an ad hoc approac Slide 5 Home Networks Home networks are envisioned to support communication between PCs, laptops, PDAs, cordless phones, smart appliances, security and monitoring systems, consumer electronics, and entertainment systems anywhere in and around the home. It allows for smart homes and aware homes. There are several design challenges for such networks. One of the biggest is the need to support the varied quality-of-service (QoS) requirements for different home networking applications. Other big challenges include cost and the need for standardization and power constrains for some devices. Slide 6 ٣
Device Networks Device networks support short-range wireless connections between devices. Such networks are primarily intended to replace inconvenient cabled connections with wireless connections. The main technology drivers for such networks are low-cost low-power radios with networking capabilities such as Bluetooth, Zigbee, and UWB. The radios are integrated into commercial electronic devices to provide networking capabilities between devices. Some common uses include a wireless headset for cell phones, a wireless USB or RS232 connector, wireless PCMCIA cards, and wireless set-top boxes. Slide 7 Sensor Networks Wireless sensor networks consist of small nodes with sensing, computation, and wireless networking capabilities, as such these networks represent the convergence of three important technologies. Sensor networks have enormous potential for both consumer and military applications. Most sensors will be deployed with non-rechargeable batteries. The problem of battery lifetime in such sensors may be averted through the use of ultra-small energy-harvesting radios. This low level of power dissipation enables nodes to extract sufficient power from the environment - energy harvesting - to maintain operation indefinitely. Slide 8 ٤
Distributed Control Systems Ad hoc wireless networks also enable distributed control applications, with remote plants, sensors and actuators linked together via wireless communication channels. Such networks allow coordination of unmanned mobile units, and greatly reduce maintenance and reconfiguration costs over distributed control systems with wired communication links. Current distributed control designs provide excellent performance as well as robustness to uncertainty in model parameters. However, these designs are based on closed-loop performance that assumes a centralized architecture,synchronous clocked systems, and fixed topology. Slide 9 Ad hoc wireless networks cannot provide any performance guarantee in terms of data rate, delay or loss characteristics: delays are typically random and packets may be lost. Unfortunately, most distributed controllers are not robust to these types of communication errors, and effects of small random delays can be catastrophic. Thus, distributed controllers must be redesigned for robustness to the random delays and packet losses inherent to wireless networks. Ideally, the ad hoc wireless network can be jointly designed with the controller to deliver the best possible end-to-end performance. Slide 10 ٥
Design Principles and Challenges An ad hoc wireless network has peer-to-peer communication, networking and control functions that are distributed among all nodes, and routing that can exploit intermediate nodes as relays. Ad hoc wireless networks can form an infrastructure or node hierarchy, either permanently or dynamically. For example, many ad hoc wireless networks form a backbone infrastructure from a subset of nodes in the network to improve network reliability, scalability, and capacity. If a node in this backbone subset leaves the network, the backbone can be reconfigured. some nodes may be chosen to perform as base stations for neighboring nodes Slide 11 ٦