Wireless Multi-hop Ad-hoc Networks: A Review <s> I. Introduction <s> When n identical randomly located nodes, each capable of transmitting at W bits per second and using a fixed range, form a wireless network, the throughput /spl lambda/(n) obtainable by each node for a randomly chosen destination is /spl Theta/(W//spl radic/(nlogn)) bits per second under a noninterference protocol. If the nodes are optimally placed in a disk of unit area, traffic patterns are optimally assigned, and each transmission's range is optimally chosen, the bit-distance product that can be transported by the network per second is /spl Theta/(W/spl radic/An) bit-meters per second. Thus even under optimal circumstances, the throughput is only /spl Theta/(W//spl radic/n) bits per second for each node for a destination nonvanishingly far away. Similar results also hold under an alternate physical model where a required signal-to-interference ratio is specified for successful receptions. Fundamentally, it is the need for every node all over the domain to share whatever portion of the channel it is utilizing with nodes in its local neighborhood that is the reason for the constriction in capacity. Splitting the channel into several subchannels does not change any of the results. Some implications may be worth considering by designers. Since the throughput furnished to each user diminishes to zero as the number of users is increased, perhaps networks connecting smaller numbers of users, or featuring connections mostly with nearby neighbors, may be more likely to be find acceptance. <s> BIB001 </s> Wireless Multi-hop Ad-hoc Networks: A Review <s> I. Introduction <s> The capacity of ad-hoc wireless networks is constrained by the mutual interference of concurrent transmissions between nodes. We study a model of an ad-hoc network where n nodes communicate in random source-destination pairs. These nodes are assumed to be mobile. We examine the per-session throughput for applications with loose delay constraints, such that the topology changes over the time-scale of packet delivery. Under this assumption, the per-user throughput can increase dramatically when the nodes are mobile rather than fixed. This improvement can be achieved by exploiting node mobility as a type of multiuser diversity. <s> BIB002
In early days, most of the wireless networks were wireless local area networks (WLAN) operating the IEEE 802.11 WiFi protocol in infrastructure mode. The infrastructure consists of a base station, also called an access point that is owned by a company or a network operator. Such networks were centralized and the base station controls the access to the communication channel. The base station was also used to connect the WLAN to the company network or to the Internet. IEEE 802.11 offers a second mode, the ad-hoc mode. It is used now a days in many emergency application scenarios BIB002 . For example, military operations, relief and disaster recovery operations etc. In this mode, there is no base station, and devices within the same wireless LAN communicate directly (i.e., in a single hop). An extension of wireless LAN operating in ad hoc mode are multi-hop ad hoc networks. They are typically deployed in large areas. A wireless multi-hop ad-hoc network is a network of nodes (e.g. computers, mobile nodes etc.) connected by wireless communication links. The links are usually implemented with digital packet radios. The transmission range of radio is very limited. Some devices might not be able to communicate directly to each other because of their limited radio range. These networks need other intermediate nodes to forward messages. In such cases, intermediary devices act as relays. In other words, the communication goes through multiple hops before reaching its final destination. This networking concept was successfully applied in several classes of networks that are penetrating the mass market BIB001 . These networks in various forms e.g. wireless sensor networks, vehicular networks, mesh networks and under various names e.g. ad-hoc networks, hybrid networks, delay tolerant networks and intermittently connected networks, are being increasingly used in military and civilian applications too. They are not relying on existing infrastructure hence their deployment cost is low. Also, they offer a potential throughput gain. These characteristics make multi-hop ad hoc networks a promising technology. The remaining part of this paper is organised as follows. Section 2 gives a background of wireless multi-hop ad-hoc networks, as well as its application areas and various research issues are also discussed. Section 3 describes the main evolutions of wireless multi-hop ad-hoc networks specially the opportunistic networks. In section 4, routing challenges related to wireless multi-hop networks are discussed. Finally, section 5 concludes the paper and present the future work.