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In recent years, wireless network wireless transmission has developed by leaps and bounds, and many new wireless communication technologies and standards have emerged for different applications and needs, and wireless mesh networks are one of the new technologies that have attracted much attention. WMN is a new networking technology, namely mesh network. Its topological structure is dynamic, with self-organizing and self-healing functions, that is, it can automatically form a network without human intervention, and each terminal can join or exit freely. When the information is transmitted, the information is continuously forwarded to the destination terminal through multi-hop. If this technology is used to self-organize wireless sensors, Wi-Fi (Wireless Fidelity), WiMAX (worldwide inter-operability for microwave access) and other technologies, they can extend their application range and strengthen their functions, thereby forming a wireless network. Sensor network, improve the coverage of wireless local area network, build metropolitan area network. Also because of its broad application prospects, it has been paid more and more attention and applied to life and work.
1 WMN technology
1.1 Technical principle
Wireless Mesh networks are low-power multi-hop (multihop) systems. The way they process messages is to pass information packets from one node to another until the information packets reach the destination. The point-to-point network node filters out all the information packets, leaving only its own information packets. The difference is that the mesh network node receives the information packets to be transmitted to other nodes and transmits them again. Each node of the wireless Mesh network can be used as an access terminal, can also have routing and information forwarding functions, and has a high degree of freedom in networking. The wireless Mesh network operates like the Internet, and provides multiple redundant communication paths from source to destination. If a path stops working due to hardware failure or interference, the mesh network will automatically change the routing of information packets to make them traverse an alternative path.
1.2 Network structure
There are two types of WMNs nodes: routers or clients. The routers that form the backbone of the network are very mobile. They provide gateways and bridges that connect mesh networks with other networks (such as the Internet, cellular networks, IEEE802, and sensor networks). Function: Clients can be static or mobile, and they can be networked by themselves or together with the routers of the mesh network.
1.3 Main features
Wireless multi-hop. By reducing the transmit power of wireless nodes, multi-hop transmission between nodes is realized, which can effectively reduce node energy consumption, reduce interference between nodes, increase the spatial reuse of wireless channels, and increase network capacity.
Self-organization and self-repair capabilities. The wireless mesh network is flexible, easy to configure, self-healing, and the nodes are distributed in a mesh pattern. The network has strong scalability and can realize multipoint-to-multipoint wireless communication.
Mobility. Depending on the type of node, the routing node is required to have the least mobility and the client node can move flexibly.
Access method. Flexible and diversified, it can be separately networked with Internet, cellular network, sensor network, etc.
Energy consumption method. There is usually no strict limit on the energy consumption of routing nodes, while client nodes are usually required to implement power-efficient protocols.
Compatibility and interoperability. It is compatible with existing wireless networks and has strong interoperability.
2 WMN protocol
Looking at the topology and architecture analysis of WMN from another angle, it has absorbed the advantages of both star and mesh networks, and is a seamless integration of the two. And this fusion is accomplished by implementing the WMR (Wireless Mesh Routing) protocol on the network nodes (see Figure 1).
Figure 1 WMN protocol based on WMP
As can be seen from Figure 1, in order to provide multiple reflection wireless routing functions, the WMR routing protocol is implemented at both the access point and the mobile node. At the same time, in order to achieve compatibility with IP, WMR is placed as an intermediate layer protocol between the MAC layer and the IP layer, so that the WMR protocol can be implemented well without major changes to other protocol layers. This makes WMR better compatible with most existing applications (including wireless standards represented by 802.11x).
3 Advantages of WMN
WMN has many advantages over traditional wireless networks
(1) The reliability is greatly enhanced
The grid topology adopted by WMN avoids the point-to-multipoint star structure, such as 802.11WLAN and cellular network, due to the centralized control of business convergence, central network congestion, interference, and single-point failure, thus bringing additional reliability Guarantee cost investment.
(2) Has a conflict protection mechanism
WMN can identify the link that causes collision and the angle between the optional link and its own link is an obtuse angle, which reduces the interference between links.
(3) Simplify link design
WMN usually requires a shorter wireless link length, which reduces the cost of the antenna (transmission distance and performance). On the other hand, reducing the transmission power will also reduce the interference between radio frequency signals of different systems and system self-interference. Finally, the wireless link design is simplified.
(4) Increased network coverage
Due to the introduction of WR and IAP, end users can access the network at any place or connect with other nodes of the 5989 series. Compared with the traditional network, the range of access points is greatly enhanced, and the utilization rate of spectrum is improved, and the system capacity Increase.
(5) Flexible networking and easy maintenance
Due to the group network characteristics of the WMN network itself, as long as a small amount of wireless equipment such as WR is added where needed, a wireless broadband access network can be formed with existing facilities. The routing feature of the WMN network makes the link interruption or partial expansion and upgrades do not affect the operation of the entire network, thus improving the flexibility and feasibility of the network, and has more powerful and complete functions than traditional networks.
4 Practical application
Mesh networks have broad application prospects in many fields such as homes, enterprises and public places.
(1) Family
An important use of wireless Mesh networks is to build home wireless networks. Home wireless Mesh networks can connect desktop PCs, laptops, HDTVs, DVD players, game consoles, and various other consumer electronic devices without complicated wiring and installation procedures. In the home wireless Mesh network, various household appliances are not only users on the Internet, but also provide access services for other devices as a component of the network infrastructure. When the number of household appliances increases, this networking mode can provide more capacity and greater coverage. Another benefit of wireless Mesh network in home applications is that it can support applications with a high concentration of bandwidth, such as high-definition video.
(2) Enterprise
At present, most of the wireless communication systems of enterprises use the traditional cellular telephone 695-type wireless link to provide users with point-to-point and point-to-multipoint transmission. The wireless Mesh network is different. It allows network users to share bandwidth, eliminates the bottleneck of the current single-hop network, and can achieve dynamic balance of network load. It is also easier to add or adjust APs in a wireless Mesh network than wired APs, with more flexible configuration, and lower installation and use costs. Especially for those enterprises that need to move access points frequently, the multi-hop structure and flexible configuration of the wireless Mesh network will be very beneficial to the adjustment and upgrade of the network topology.
(3) School
Campus wireless networks are very similar to large enterprises, but they also have their own different characteristics. One is the large scale of campus WLAN, which not only has a large geographical area and a large number of users, but also has a large amount of communication, because students will use multimedia more than ordinary enterprise users; second, the network coverage requirements are high, and the network must be able to achieve indoor and Seamless roaming between outdoors, auditoriums, dormitories, libraries and public places; thirdly, load balancing is very important. Because students often have to concentrate activities, when students use the network at a certain location at the same time, communication congestion may occur .
The traditional way to solve these problems is to install APs in high density indoors, while the number of APs installed outdoors is very small. However, due to the large changes in the user requirements of the campus network, it may often be necessary to add new APs or adjust the deployment positions of APs, which will bring a great increase in costs. The use of wireless Mesh network networking, not only easy to achieve network structure upgrade and adjustment, but also can achieve seamless roaming between outdoor and indoor.
(4) Hospital
The wireless Mesh network also provides an ideal networking solution for public places like hospitals. Due to the dense and complex structure of hospital buildings, some areas must be protected from electromagnetic radiation, so it is one of the most difficult areas to install wireless networks. The hospital's network has the characteristics of difficult wiring and high requirements for the robustness of the network. The use of wireless Mesh networking is an ideal solution to solve these problems. If you want to adjust the wireless network topology of the hospital, you only need to move the location of the existing Mesh node or install a new Mesh node. The process is very simple, and the installation of a new Mesh node is also very convenient. The robustness and high bandwidth of wireless Mesh also make it more suitable for deployment in hospitals.
(5) Tourist and leisure places
The wireless Mesh network is very suitable for places where wiring is difficult or economically uneconomical in remote locations, and broadband wireless Internet access needs to be provided to users, such as tourist sites, resorts, motels, etc. The wireless Mesh network can provide broadband services to these places at the lowest cost.
(6) Quick deployment and temporary installation
For places that require rapid deployment or temporary installation, such as exhibitions, trade fairs or disaster relief, wireless Mesh networks are undoubtedly an economical and effective networking method. For example, if you need to hold a meeting for a few days or hold an exhibition for a few days in a certain place, using a wireless Mesh network to build a network can minimize the cost.
5 Conclusion
WMN not only has broad application prospects in many fields such as households, enterprises and public places, but also in other aspects such as combining data and image acquisition modules to monitor or collect data on target objects, and is widely used in environmental detection, industry, transportation, etc. And other fields. With the continuous updating and improvement of other technologies, WMN is better integrated and complementary to each other so as to maximize its strengths and circumvent its weaknesses.
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