What Is a Mobile Ad Hoc Network?

A mobile ad hoc network is a network that combines mobile communications and computer networks, and is a type of mobile computer network. User terminals can move around within the network and maintain communications.

Chinese name: Ad hoc network
Foreign name: Ad Hoc

Solid: Multi-hop temporary autonomous system
Prototype: ALOHA Network

Overview of self-organizing networks

Mobile Ad Hoc network is a multi-hop temporary autonomous system. Its prototype is the ALOHA network established in the United States in 1968 and the PR (Packet Radio) network proposed in 1973. The ALOHA network requires a fixed base station. Each node in the network must be directly connected to all other nodes to communicate with each other. It is a single-hop network. Until the PR network, a multi-hop network in the true sense did not appear. The nodes in the network do not need to be directly connected. Instead, they can use relays to transfer information between two nodes that are far away and cannot communicate directly. . PR networks are widely used in the military field. When the IEEE developed the 802.11 standard, it proposed to rename the PR network to Ad Hoc network, which is the mobile ad hoc network we often say today.

Mobile Ad Hoc Network. On the one hand, the network information exchange uses the packet switching mechanism in the computer network instead of the circuit switching mechanism in the telephone switching network; on the other hand, the user terminal is a portable terminal such as a notebook, PDA, etc. Mobile or stationary. Each user terminal in a wireless ad hoc network has both router and host functions. As a host, the terminal can run various user-oriented applications; as a router, the terminal needs to run the corresponding routing protocol. This distributed control and centerless network structure can maintain the remaining communication capacity after some communication networks are damaged. , Has strong robustness and invulnerability.

As a distributed network, the mobile ad hoc network is an autonomous, multi-hop network. The entire network does not have a fixed infrastructure. It can be used in situations where it is not possible or convenient to use the existing network infrastructure (such as base stations, APs). Provides mutual communication between terminals. Because the transmission power and wireless coverage of the terminal are limited, two terminals with longer distances must use other nodes to perform packet forwarding if they want to communicate. In this way, a wireless multi-hop network is formed between the nodes.

Mobile terminals in the network have routing and packet forwarding functions and can form any network topology through wireless connections. The mobile ad hoc network can work independently as a separate network, or it can be connected to existing networks in the form of end subnets, such as the Internet network and the cellular network.

Ad hoc network characteristics

Mobile ad hoc networks can use the routing and forwarding functions of mobile terminals to communicate without infrastructure, thereby making up for the lack of usability of network-free communications infrastructure. Ad hoc network technology provides a solution for computer-supported collaborative work systems. The main features are:

Dynamic change of network topology of self-organizing network

In mobile ad hoc networks, due to the effects of factors such as random movement of user terminals, node startup and shutdown at any time, changes in transmit power of wireless transmitters, mutual interference between wireless channels, and terrain, mobile terminals use wireless channels The network topology structure formed may change at any time, and the way and speed of the change are unpredictable.

Self-organizing network

Mobile ad hoc networks do not have strict control centers. All nodes have equal status and are peer-to-peer networks. Nodes can join and leave the network at any time, and the failure of any node will not affect the operation of the entire network, which is highly resilient.

Ad hoc network

Because the transmission power and coverage of a mobile terminal are limited, when a terminal wants to communicate with a terminal outside the coverage, it needs to use an intermediate node for forwarding.

It is worth noting that, unlike multi-hop in general networks, multi-hop routing in wireless ad hoc networks is performed jointly by common nodes, rather than by special routing equipment.

Ad hoc network has limited wireless transmission bandwidth

The physical characteristics of the wireless channel itself determine that the bandwidth of the mobile ad hoc network is much lower than that of the wired channel. The collision, signal attenuation, noise interference, and channel interference caused by competing shared wireless channels make the actual bandwidth of the mobile terminal much smaller than the theory value.

Limitations of Ad Hoc Mobile Terminals

Mobile terminals (such as laptops, mobile phones, etc.) in ad hoc networks have the advantages of dexterity, portability, and good mobility, but at the same time their limited power, small memory, and low CPU performance make us need Consider these factors.

Application area of self-organizing network

Mobile ad hoc networks are often used in situations where there is no or inconvenient use of existing network infrastructure. The main applications are in the following areas.

Self-organizing network military communications

In modern battlefields, because there is no infrastructure such as base stations, military personnel equipped with mobile communication devices, military vehicles, and various military equipment can exchange information through mobile ad hoc networks in order to maintain close contact and complete collaboration. Combat missions; military vehicles and equipment equipped with audio sensors and cameras can also transmit the location and environmental information collected in the target area to the processing node through a mobile ad hoc network; the fleet battle groups that need to communicate can also use mobile autonomous Organize networks to establish communications without having to rely on terrestrial or satellite communications systems. Mobile ad hoc network technology has become the core technology of the US military's tactical Internet. The US military's digital radio and wireless Internet controllers have adopted mobile ad hoc network technology.

Ad hoc network mobile conference

At present, people often carry portable terminals such as notebooks, PDAs (personal digital assistants) to participate in various meetings. Through mobile ad hoc network technology, various mobile terminals can be quickly organized into wireless networks without using routers, hubs, or base stations to complete questions, exchanges, and data distribution.

Ad hoc network mobile network

Mobile terminals generally do not have a fixed IP address related to the topology, so they cannot be connected through traditional Mobile IP protocols, and mobile multi-hop networking is required. Because the flat topology is used, there is no problem of address change, so that these mobile terminals are still like in a standard computer environment.

In addition, in practical applications, in addition to local communication, the ad hoc network can also be used as an end subnet to connect to an existing network infrastructure, such as the Internet or a cellular network, through a gateway. As an end subnet, only information originating from or destined to nodes within the autonomous system is allowed in and out, and other information is not allowed to pass through the autonomous system. It can be seen that mobile ad hoc networks can become a wireless access method for various communication networks.

Ad hoc networks connect domain networks

A personal area network (PAN) contains only devices that are closely related to a person. These devices cannot connect to the wide area network. Bluetooth technology is currently a typical personal area network technology, but it can only achieve indoor short-distance communication. Therefore, mobile ad hoc networks provide the possibility to establish multi-hop interconnection between PAN and PAN.

Ad hoc network emergency services and disaster recovery

When network infrastructure fails and becomes unusable due to natural disasters or various other reasons, it is very important to quickly restore communication. With the help of mobile ad hoc network technology, temporary networks can be quickly established and network infrastructure can be extended, thereby reducing the harm caused by rescue time and disasters.

Ad hoc network wireless sensor network

Wireless sensor networks are a large application area of mobile ad hoc network technology. The sensor network uses wireless communication technology. Due to the small transmission power, it can only use multi-hop transmission for communication. The distributed sensor nodes are self-organized into a network to complete various application tasks.