802. 1 1a extends the physical layer of the 802. 1 1 standard, and specifies that this layer uses the frequency band of 5G Hz. The standard adopts OFDM (Orthogonal Frequency Division) modulation technology, and the transmission rate ranges from 6 Mbps to 54 Mbps. * * * There are12 non-overlapping transmission channels. This rate can meet indoor and outdoor applications.
802. 1 1b specifies that the frequency band is 2.4GH z, the modulation mode is CKK, and * * * has three non-overlapping transmission channels. The transmission rate can be automatically reduced from 1 1Mbps to 5.5Mbps, or adjusted to 2Mbps and 1Mbps according to the direct sequence spread spectrum technology to ensure the normal operation and stability of the equipment.
802. 1 1g is the third transmission standard, and * * * has three non-overlapping transmission channels. Although it also runs at 2.4GHz, the standard adopts the same modulation mode as the 802. 1 1a standard, which makes the network reach a high transmission rate of 54Mbps, while the price of products based on this standard is only slightly higher than that of products based on 802.1/b standard.
802. 1 1e will solve the QoS characteristics of 802. 1 1 network. Different from Ethernet, it uses MAC layer instead of TDMA technology, and adds extra error correction function in important communication. At present, the standard has not been finalized, because the service level is still controversial, and how to realize the specific service level is still a problem.
802. 1 1f mainly solves the shortcomings of 802. Internet interconnection 1 1. When users roam between two different switching network segments (wireless channels) or access points of two different types of wireless networks, it is very important for wireless local area networks to have the flexibility of cellular phones.
802. 1 1h tries to be better than 802. 1 1a in transmission power and wireless channel selection, and together with 802.438+0 1A, it will become a widely accepted standard in Europe. 802. 1 1i mainly overcome the shortcomings of 802. 1 1 in security. Different from WEP, the working group in charge of this standard has not yet selected the authentication protocol: some members want to adopt a new system called "OCB", but it belongs to three different patents; It is a brand-new standard based on AES encryption algorithm. Others prefer a universal password.
802. 1 1j is still in the pipeline, and my EEE has not formally established a special working group to discuss it. At the drafting stage, the frequency bands used by 802. 1 1a and HiperLAN2 networks will be adopted.
802. 1 1n, the next new wireless specification, the data transmission rate of this new specification has not yet been determined, but at least it will be above 100MBps.
Wireless LAN is widely used in practice because of its mobility and high-speed data transmission.
① Between buildings
It is simple and cheap to build a network connection between buildings instead of a private line. Catering and retail catering services can use WLAN products to directly input and transmit the contents of guests' orders from the dining table to the kitchen and counter. When retailers promote sales, they can use WLAN products to set up temporary checkout counters.
② medical treatment
Using portable computers with WLAN products to obtain real-time information can help medical staff avoid delaying the treatment of the wounded, unnecessary paperwork, delaying the circulation of documents and misdiagnosis, and improve the quality of care for the wounded.
③ Enterprise
When employees in enterprises use WLAN products, no matter where they are in the office, they can send emails, share files and browse the Internet at will.
④ Warehouse management
With the application of wireless network, general warehouse personnel can immediately input the latest data into the computer warehouse system.
⑤ Container terminal
In general, the bridge crane in the container yard can send real-time information back to the office when the container is transferred, which is beneficial to the related operations line by line.
⑥ Monitoring system
Generally, remote places that need to be monitored can send remote images back to the main control station through wireless network due to wiring difficulties.
⑦ Exhibition venue
For example, in general electronic exhibitions and computer exhibitions, it is a good choice if you can use wireless networks because of the extremely high network requirements and messy wiring. Broadband wireless access system is a fixed wireless access system, which provides high-speed, two-way data, voice or video services by point-to-multipoint transmission, and can be used as a powerful means for applications such as DDN private line, frame relay or E 1 transmission, high-speed Internet access, local area network and metropolitan area network interconnection. Broadband wireless access system can be divided into MMDS (multi-channel multipoint distribution service) and LMDS (local multipoint distribution service) according to different frequency bands. Broadband wireless access system consists of base station and remote station. A base station can communicate with multiple remote stations at the same time within its own wireless coverage. The base station collects the data of the remote station, and then accesses the backbone data network through optical ring or microwave SDH loop.
Advantages of broadband wireless access system include:
1) The network structure is very flexible, extensible and reusable.
2) The network is built quickly and opened quickly.
3) Less initial investment and short return period.
4) Rich business interfaces
5) High quality, high reliability, large capacity, low price and mature technology.
The services provided by broadband wireless access system include:
1) is used for connectionless services.
2) Internet access (WWW browsing, e-mail, high-speed file transfer, etc. )
3) Local area network and metropolitan area network interconnect VOD, distance education, telemedicine and other value-added services.
4) Connection-oriented service (circuit or circuit simulation mode)
5) Ordinary telephone service
6) Circuit bearer services lower than E 1, such as n×64kbit/s, etc.
7) Frame Relay
8) Digital circuit with E 1 or higher carry service.
The typical user groups of this system are
1) business building
2) Group users (mainly group companies, industrial and mining enterprises, banks and government agencies)
3) Hotel
4) Business users (Internet cafes and other entertainment places)
5) Community users
6) FSO technology for private network users is a wireless transmission technology based on optical transmission mode and using infrared laser to carry high-speed signals. It uses laser as carrier and air as medium to realize point-to-point or point-to-multipoint connection. Because its equipment also uses light emitting diode or laser diode as light source, it is also called virtual optical fiber. FSO technology uses a low-power infrared laser beam as a carrier to transmit data between transceivers located on the roof or outside the window. Infrared band is smaller than microwave band, which is more flexible and convenient. The working frequency band of FSO system is above 300GHz, and the application of this frequency band is not stipulated internationally, so it can be used for free. FSO technology has the same bandwidth transmission capacity as optical fiber, and it can even realize wavelength division multiplexing (WDM) technology in free space by using similar optical transmitters and receivers. FSO technology has incomparable advantages over microwave, such as low rain attenuation, no need to apply for frequency band, easy equipment upgrade, etc. Its open interface supports instruments from various manufacturers. At present, the products on the market support the highest transmission rate of 2.5Gbps, and the maximum transmission distance is 4 kilometers. However, FSO technology has no upper bandwidth limit in theory, and 160Gbps equipment is under development.
FSO technology can transmit data, voice and video, and has the characteristics of high bandwidth, rapid deployment, reasonable cost, small size and convenient opening. In large-scale collective communication, emergency service opening, routing backup and other emergency communications, it has the advantages of rapid opening and convenient dismantling. Moreover, FSO equipment can get the right to use the roof more conveniently than microwave equipment that needs antennas, and it can also be installed indoors through windows, which is sometimes extremely critical for operators in large and medium-sized cities in China.
FSO products are installed quickly and conveniently, with the current maximum speed of 2.5G and the longest transmission distance of 4km. FSO products are very useful in the construction of short-distance high-speed networks such as local networks and edge networks. At present, FSO products are mainly used in places where the wiring is not suitable or the wiring cost is high, the construction is difficult, and the approval of municipal departments is difficult, such as between high-rise buildings in urban areas, between buildings on both sides of expressways (railways), on both sides of rivers that are difficult to bridge, ancient buildings, mountains, islands, desert areas and so on. In addition, FSO equipment can also be used for loop construction of mobile base stations, connection between scattered enterprise LANs and emergency communication. For commercial applications such as banks, securities and government agencies that need stable services, FSO products can be used as optical fiber backup equipment to prevent service interruption. In view of the quick and simple installation of FSO products, it can be used as a temporary communication connection in exhibitions, short-term rented buildings, outdoor temporary workplaces or earthquake emergency sites.