Mobile ad hoc network is a mobile communications and computer networks combined network, a mobile computer network, the user terminal can move freely within the network and maintain communications. Organization Network Overview Mobile Ad (Ad Hoc) network is a multi-hop temporary autonomous system, its prototype is the United States as early as 1968, and after the establishment of the ALOHA network in 1973's PR (Packet Radio) network. ALOHA network needs a fixed base station, each node in the network and all other nodes must be connected directly to communicate with each other, is a single-hop network. Until the PR network, only a true sense of the multi-hop network, each node in the network does not require a direct connection, but be able to relay the way, in two very far away and can not communicate directly transmit information between nodes . PR Web is widely used in military field. In the development of IEEE 802.11 standards, the proposed network will be renamed PR Ad Hoc networks, that today we often say that the mobile ad hoc networks.
Mobile ad hoc networks. One hand, network information exchange using computer networks packet switching mechanism, rather than the circuit switched telephone network exchange mechanism; the other hand, the user can move the portable terminal is a terminal, such as a laptop, PDA, etc., the user can at any time in mobile or stationary. Wireless ad hoc networks each user terminal are two functions of both routers and hosts. As host, the terminal can run a variety of user-oriented applications; as routers, terminal need to run appropriate routing protocols. Such distributed control and no central part of the network structure can maintain the communications network after the destruction of the remaining communication capabilities, with strong robustness and survivability.
As a distributed network, mobile ad hoc networks is an autonomous, multi-hop network, the network has no fixed infrastructure, can not use or inconvenient to use existing network infrastructure (such as base stations, AP) in the case, provide communication between the terminal. As the wireless terminal transmission power and coverage is limited, so far away from the two terminals if you want to communicate with other nodes must be grouped by means of forwarding such nodes form a wireless multi-hop network.
Mobile terminals in the network routing and packet forwarding with, constitute a wireless connection can be any network topology. Mobile ad hoc network can work independently as a separate network, can also be the end of the subnet in the form of access to existing networks, such as the Internet network and the cellular network. Characteristics of self-organizing network Mobile ad hoc networks can use the routing forwarding mobile terminals, in the case of non-infrastructure communication to compensate for the non-network communication infrastructure deficiencies that can be used. Since the networking technology for computer supported cooperative work system provides a solution, the main features are: (1) dynamic network topology In mobile ad hoc networks, due to random mobile user terminals, nodes always-on and off, writing device wireless transmit power changes, the mutual interference between wireless channel and the impact of a combination of factors such as terrain, the mobile terminal through the wireless channel between the formation of the network topology may change at any time, and changes in the way and speed are unpredictable. (2) self-organizing network of centers without Mobile ad hoc network does not have a strict control center, the status of all nodes are equal, is a peer to peer network. Nodes can join at any time and leave the network, any node failure will not affect the operation of the entire network, with strong survivability. (3) multi-hop network As the mobile terminal transmit power and limited coverage, with coverage when outside the terminal to terminal communication, the need to use intermediate nodes to forward. As shown below. It is noteworthy that, in general the different multi-hop network, wireless ad hoc networks in multi-hop routing is done by the ordinary nodes to work together, rather than by specialized equipment to complete the route. (4) wireless transmission bandwidth is limited The physical characteristics of the wireless channel itself determines the mobile self-organizing network bandwidth than cable channel is much lower, and competition generated by the collision shared wireless channel, signal attenuation, noise and channel interference and other factors make the mobile terminal is far less than the actual bandwidth theoretical value. (5) the limitations of mobile terminals Self-organizing network of mobile terminals (such as notebook computers, mobile phones, etc.) with smart, light, mobility and good, but its power is limited, small memory, CPU performance and low limits, so we develop the application, need to consider these factors.
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