802.11 is a wireless local area network standard announced by the IEEE (The InsTItute of Electrical and Electronics Engineers) in 1997. It is suitable for communication between wired stations and wireless users or wireless users.
Specifications for 802.11:â– 802.11 -- The initial specification adopts Direct Sequence Spread Spectrum (DSSS) or Frequency Hopping Spread Spectrum (FHSS) to develop the application in the RF RF band of 2.4 GHz. 1Mbps, 2Mbps and many basic signal transmission methods and service transmission rate specifications.
â– 802.11a -- a derivative of 802.11 that provides a maximum of 54 Mbps in the 5.8 GHz band and uses the orthogonal frequency division mulTIplexing encoding scheme to replace 802.11 FHSS or DSSS.
â– 802.11b -- (so-called high-speed wireless network or Wi-Fi standard), re-released the IEEE802.11b high-speed wireless network standard in 1999, using DSSS technology in the 2.4GHz band, and due to the emergence of this derivative standard, Increases the transmission speed of the original wireless network to 11 Mbps and is compatible with Ethernet.
â– 802.11g -- Provides speed specifications above 20 Mbps on the 2.4 GHz band.
â– 802.11e -- defines the quality of the WLAN (quality-of-service), such as support for voice ip;
â– 802.11h -- complements 802.11a to comply with European specifications for 5ghz WLANs;
â– 802.11i -- wireless security standard, wpa is a subset of it;
â– 802.11j -- the equivalent of 802.11h protocol used in Japan;
â– 802.11k - Radio Broadcast Resource Management. By deploying this feature, service operators and enterprise customers will be able to more effectively manage the connection between wireless devices and access point devices/gateways.
â– 802.11n -- A proposed specification that is expected to be adopted in 2006, which will double the transmission rate of 802.11a/g WLANs;
â– 802.11p - vehicle access.
â– 802.11r - "fast roaming". Although it may not be obvious now, Wi-Fi mobile devices will soon need to have the ability to quickly switch between different networks while users or users are moving.
â– 802.11s - "mesh network", each device in the network can relay data to a node away from the access point.
â– 802.11t - wireless network performance.
â– 802.11u - interactivity with other networks.
â– 802.11v - wireless network management. 802.11v is mainly for operators, and is committed to enhancing the services provided by Wi-Fi networks.
802.11n protocolWith up to 600 Mbps, the emerging 802.11n standard is the next generation of wireless networking technology that delivers the speed, range and reliability needed to support the most bandwidth-sensitive applications. 802.11n combines multiple technologies, including SpaTIal MulTIplexing MIMO (Multi-In, Multi-Out), 20 and 40MHz channels, and dual bands (2.4 GHz and 5 GHz) for Forms a high rate while communicating with previous IEEE 802.11b/g devices.
Multiple Input Multiple Output (MIMO) or Multiple Receive Multiple Antenna (MTMRA) technology is a major breakthrough in smart antenna technology in the field of wireless mobile communications. This technology can double the capacity and spectrum utilization of communication systems without increasing bandwidth, and is a key technology that must be adopted in a new generation of mobile communication systems.
Introduction to 802.11n technology MIMO and OFDM
802.11n focuses on high-throughput research and plans to increase the transmission rate of WLANs from 54 Mbps for 802.11a and 802.11g to more than 108 Mbps, with a maximum rate of 320 Mbps or even 500 Mbps. Such a high rate of course has technical support, and OFDM technology, MIMO (multiple input and multiple output) technology is the key.
OFDM technology is a type of Multi-Carrier Modulation (MCM) that was once adopted in the 802.11g standard. The core is to divide the channel into a number of narrowband modulation and transmit orthogonal subchannels, and make the signal bandwidth on each subchannel smaller than the relevant bandwidth of the channel, to reduce the mutual interference between the carriers, and improve the spectrum. Utilization technology.
OFDM also enables uplink and downlink asymmetric transmissions by using different numbers of subchannels. However, OFDM technology is susceptible to frequency deviation and has a high peak-to-average power ratio (PAR). However, space-time coding, diversity, interference suppression, and smart antenna technology can be used to maximize the reliability of the physical layer. 802.11g Although similar techniques are used, the combination with MIMO technology in 802.11n is naturally inferior.
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