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Views: 45 Author: Site Editor Publish Time: 2020-02-07 Origin: Site
MESH ad hoc network is a new type of wireless network that is completely different from traditional wireless networks. It is a technology that dynamically establishes new links to connect with other nodes. It has the advantages of self-organizing network, self-repairing, multi-hop cascading, and node self-management.
At present, the industry's MESH ad hoc network mainly uses the following technologies:
1) According to the networking frequency band, Mesh is divided into multi-frequency multi-channel networking and single-frequency networking. Single-frequency networking uses a single frequency for transmission and reception, reducing bandwidth capacity by half. In multi-frequency and multi-channel networking, the device uses multiple orthogonal frequencies for different links, which can increase system throughput.
2) In terms of radio frequency technology, in order to improve transmission rate and performance, technologies such as OFDM, MIMO, and smart antennas have been widely used in recent years.
3) In terms of resource scheduling, it is usually divided into CSMA / CA mode and TDMA mode. CSMA / CA uses a resource competition mode, but when there are many nodes and hops, and the network load is high, the effective utilization of resources is low. TDMA mode is a scheduling mechanism based on time allocation. When the network load is heavy, the efficiency is higher.
4) In terms of network routing algorithms, unlike the RIP and OSPF routing protocols used by fixed routing, common Mesh wireless routing algorithms include DSDV, DSR, AODV, etc.
In the early days, broadband MESH products widely used CSMA / CA-based Wi-FiMESH technology. The multi-frequency modular design can provide high-capacity, low-cost wireless access solutions in the ISM band. Wi-Fi MESH products are widely used in the construction of "Wireless Broadband Cities" in European and American countries, and domestic operators, schools, enterprises, factories, etc. are also widely used. During this period, a large number of Wi-FiMESH manufacturers such as SkyPilot and Azalea appeared. However, after the commercialization of 3G / 4G, the wireless broadband access market has shrunk sharply, and many manufacturers have closed down.
Wi-Fi MESH is not suitable for emergency communication and other industries due to issues such as frequency bands, bandwidth, and stability. MESH products that use the same frequency TDMA method have become hot spots in the industry. This type of product generally adopts FPGA + ADC chip architecture, which can flexibly design the underlying wireless communication protocol according to the channel characteristics of the application scenario, and widely uses OFDM, MIMO and other technologies. Products using this solution have higher costs, higher power consumption, and longer product development cycles. There are many companies adopting this solution in the market.
In addition, there is a MESH solution using LTE-related technologies, which fully integrates the LTE physical layer technology and specially designs its frame structure. Different modulation and coding methods can be applied to adapt to different channel changes to obtain maximum transmission efficiency. LTE is a very complete and mature technology, and its reliability and stability can be guaranteed. However, this type of solution has high development thresholds, large investment, and fewer companies that can do underlying research and development. At present, Chenxin Technology Co., Ltd., a subsidiary of China Xinke Group, has developed a MESH solution based on the LTE protocol on its SDR chip CX1860. It adopts a private wireless communication protocol with high security and reliability, and supports QoS mechanism to ensure the quality of wireless transmission services. The algorithm fully considers the multi-path channel environment and optimizes the design. It can also achieve long-distance high-performance transmission with the use of an omnidirectional antenna, up to 150 km. The solution has the flexibility of the FPGA solution and the integration degree. It also has advantages in power consumption, which is convenient for developing miniaturized terminal products. Related manufacturers can quickly develop their own MESH products based on this solution.
The MESH self-organizing network has been used in armed police, fire protection, civil air defense emergency, three defense emergency, water conservancy and flood prevention, power inspection, power rescue, "Xueliang Project", railway rescue, maritime law enforcement, sea surveillance inspection, customs border control, terminal monitoring, forest Fire prevention, oil field anti-theft, military reconnaissance, television broadcasting and other fields. Provide real-time mobile transmission of high-quality images, voice, and data in a variety of complex environments such as cities, seas, and mountains.
In recent years, most of the "Xueliang Project" projects have been concentrated in cities, and the work sinking to counties, townships and towns is still weak. One of the reasons for the slow implementation of the "Xueliang Project" in the county and township areas is that the infrastructure in some rural areas is relatively weak, and there is no optical fiber network resource that meets the requirements. At the same time, topography and other reasons have made the construction of wiring difficult and expensive. In rural, mountainous, grassland, and other sparsely populated areas, the use of wireless MESH video surveillance technology in the "Xueliang Project" construction project has the following advantages:
1) Compared with wired transmission, wireless transmission can save the cost of fiber optic cables, and it is fast and convenient to deploy, easy to maintain, and save construction labor costs;
2) There is no random connection of optical cables; it does not affect existing lines and reduces conflicts with other line departments;
3) Compared with wireless bridges, the MESH multi-hop feature enables long-distance non-line-of-sight transmission. It can solve the problem that the poles used in the "Xueliang Project" are generally only a few meters in height, and there are usually trees, buildings, mountains, etc. between wireless devices, which prevents transmission.
4) Compared with the Wi-Fi bridge by increasing the transmission power and using directional antennas, LTE MESH can achieve higher receiving sensitivity and use omnidirectional antennas for long-distance transmission, which can avoid the complicated installation of directional antennas and require the guidance of technical staff. Prone to problems such as skew.
Equipment miniaturization and portability are one of the future development trends of MESH products. On the premise of fully considering the application scenarios and ensuring the necessary functional performance, research on lightweight and smart technology to meet the requirements of single-person carrying and unmanned airborne.
In the field of emergency communications, Mesh ad hoc network technology is also widely used. The integration of Mesh with other private network communications, satellite communications and other systems is also the focus of future development.
