The outstanding structural characteristics and research and development status of WiFi long-distance wireless ad hoc networks, WiFi long-distance wireless ad hoc networks mainly form long-distance data transmission in the form of multi-hop interconnection through a group of equal nodes, connect nodes through wireless channels, and allow nodes at the same time. The dynamic movement between, its network topology can also make different changes according to different environmental conditions, because each node has a host and router functions equally, so even if there is damage or failure between each node, adjacent nodes Broken nodes can still be selectively replaced. In the WiFi long-distance wireless ad hoc network, each node can interact with the machine as a host, and can dynamically update and maintain the network according to the routing protocol.

Features of WiFi long-distance wireless ad hoc network

(1) The dynamic node structure and distributed networking are different from the past networking methods. The nodes have a high degree of autonomy, which can disperse the network control capability to each node.

(2) Flexible network structure, wireless ad hoc network is divided into equal structure (that is, plane network structure) and hierarchical structure. There are multiple paths between nodes in the plane network structure, which has the characteristics of balancing load and optimizing routing, and has strong security. However, the coverage is small, and the control cost of a dense network of nodes is high. The hierarchy is divided into clusters, and each cluster consists of the first node of the cluster and the cluster nodes. Clusters in the hierarchical structure can be specified in advance or selected using a certain algorithm. The role of the first node of the cluster is to forward data.

WiFi long-distance wireless ad hoc network comparison of two structures

In distributed operation, nodes are connected to each other through a distributed routing protocol, and each node is equal, acting as both a host and a router, and the exit of a node will not affect the entire network.

In terms of ad hoc network routing protocols, DSR, AODV, OLSR and ZRP are currently recognized wireless ad hoc network routing protocols. These protocols usually establish routing tables through broadcast multicast, with the core of reducing broadcast storms. Routing protocols must be studied, and until today, it is still the subject of ad hoc networks, including OLSR (Optimized Link State routing) and other flat topology proactive routing protocols have been regarded by IETF as the routing protocol standard for WiFi long-distance wireless ad hoc networks. It uses two control packets, the Hello packet and the TC (TopolpgyControl) packet.

OLSR uses periodic broadcast Hello packets to establish the state of neighbor nodes. The link status between nodes includes: asymmetric link, symmetric link, MPR link (MultiPointrelay) and invalid link. Due to the existence of MPR nodes, the OLSR routing protocol can achieve selective flooding instead of indiscriminate non-selective flooding, which reduces a certain network cost. OLSR obtains two tables required for route calculation through Hello packets and TC packets: neighbor table and topology table. On the basis of these two tables, the node uses the Dijkstra shortest path algorithm node to calculate the routing table at the current moment.

AODV protocol (ADHocondemanddistancevector) is a reactive routing protocol. It does not maintain the global transmission of information across the network. The node considers that a valid path is one that transmits at least one packet within the time set for that path. Therefore, in AODV, a route discovery packet can be created and declared only when the source node must connect to the destination node and there is no valid path. AODV builds the entire routing table dynamically, and each node maintains a counter to delete unused or invalid routes. The main disadvantage of AODV is that it does not support asymmetric links. It only supports symmetric links where both parties can send packets.

DSR is also a widely used routing protocol. Since each packet in the DSR protocol contains a complete list of node routes, all nodes sending or receiving packets will store routing information for backup. Whether nodes move at any time or keep moving, DSR will quickly change the network topology to maintain better performance.

The ZRP protocol (Zonerouting Protocol) combines the characteristics of the pre-routing protocol and the reactive routing protocol, and limits the transmission range of the node activity protocol update packet to a certain number of areas, thereby reducing the cost of routing control packets. When communicating with nodes outside the area, the selection of reactive routing protocols is done.

Research and development status of WiFi long-distance wireless ad hoc network era

As a wireless network form different from the traditional base station terminal architecture, the wireless ad hoc network can forward data and route functions in any harsh environment due to its flexible nodes, and is widely used in military and civilian fields, common military combat exercises , jungle reconnaissance exercises, etc., the civilian field is more extensive, covering many application scenarios of temporary communication systems such as fire emergency, disaster emergency rescue, local anti-terrorism, border guard, mine survey, etc. Its unique communication method, which integrates base stations and terminals, is common The single-soldier handheld mesh equipment, vehicle group network communication platform, unmanned system communication platform and other transmission equipment can be called wireless base station platform.

Of course, the WiFi long-distance wireless ad hoc network itself comes from military needs. It also replaces its unique military requirement function after entering the civilian domain. Common non-center anti-destructive, distributed routing, multi-hop nodes, fast networking, etc., can quickly provide satellite technology, front-end audio and video information collection, on-site radio dispatch and command, relay network relay and other business coordination according to on-site needs. access.

With the continuous development of satellite technology, the research of wireless ad hoc network in the field of satellite communication is also increasing. Foreign research on wireless ad hoc networks is also very early. For example, Tsai et al. proposed low-cost distributed routing protocols Darting, Karapantazis, etc., based on the need to reduce routing expenses, drawing on the dynamic source routing (Dynamic Source Routing, DSR) routing idea in Ad-hoc networks. , reducing routing overhead by forming the smallest routing request area.

Compared with traditional networks, the characteristics of WiFi long-distance wireless ad hoc networks are as follows:

(1) The topology structure is changeable, and the network nodes can be assigned any movement as needed, and make different strains with the movement of the nodes.

(2) Flexible link bandwidth moves with nodes. For better communication performance, the communication link can vary with the distribution of node bandwidth.

(3) Due to the mobility characteristics of network nodes, most nodes do not have continuous energy, so energy-saving design needs to be considered.

Since wireless ad hoc networks have multi-hop characteristics triggered by wireless communication, they face wireless mobile communication and network configuration device discovery, traditional problems (bandwidth optimization, power control, transmission quality improvement, etc.). Topology requires a new research topic such as maintenance, addressing and automatic routing.

In order to solve the problems associated with wireless ad hoc network routing protocols, many academic organizations are also working to standardize wireless ad hoc network routing protocols. Including the OLSR protocol (OptimizedLinkStaterotingprotocol), the AODV protocol (Adhocondemandistancetorotingprotocol), and the DSR protocol (Dynamicsourcerotingprocol) submitted by the MANET working group and used as the routing protocol specification. In order to meet the needs of ad hoc network routing, it is necessary to choose a routing protocol that is more in line with the actual project.