1. <dd id="jcf9u"><track id="jcf9u"></track></dd> <em id="jcf9u"><strike id="jcf9u"></strike></em>
      1. <th id="jcf9u"></th><dd id="jcf9u"><pre id="jcf9u"></pre></dd>
        
        
        <li id="jcf9u"></li>
      2. <th id="jcf9u"></th>

            Location:Home > News > Industry news

            What is the knowledge of WIFI technology?

            Date:2017-12-11 09:38:09 Hits:3516

            WiFi concept:

            WiFi is one of the most popular technologies in WLAN (Wireless Local Area Network), which is based on IEEE 802.11 series protocols.

            The original intention of WiFi is a certification mark, which is guaranteed to be compatible with each other through the 802.11 protocol. The global certification authority is the WiFi Alliance (WFA), predecessor of WECA (Wireless Ethernet Compatibility Alliance).


            WiFi basic principles of work:

            Half double time division system: the same area, the same frequency point / channel, and only one device can send messages at the same time.





            Work model:

            The main use of DCF (distributed coordination, Distributed Coordination Function), that is, through CSMA/CA (carrier intercept / collision avoidance / collision avoidance, Carrier Sense Multiple Access with Collision Avoidance) technology to achieve channel sharing.

            There are many WiFi devices / terminals in the environment, and the overall transmission efficiency will be reduced rapidly, and all the time will be used to transmit the signaling and can not communicate with the normal data.



            1709024862.jpg




            WiFi technical parameters



            The main five parameters are frequency band, speed, bandwidth, number of space flow and MU-MIMO.





            1) frequency band: two main bands 2.4GHz, 5GHz, 2.4GHz and 5GHz band.

            Radio signal attenuation formula: Los=32.4+20lg (F) +20lg (R)

            Among them, Los (dB) is attenuation, F (MHz) is frequency, and R (km) is the distance.

            It can be obtained that the attenuation of 2.4GHz is slow, the performance of wall through is good, the attenuation of 5GHz is fast, and the performance of through wall is poor.

            Note: through wall performance is good, which means wide coverage, but at the same time, it also means receiving a wide range of interference sources.

            Specific:

            2.4GHz: China has opened 13 channels (2.402~2.483GHz), but North America only has 11 channels.

            Application protocol: 802.11b/g/n, where 802.11n supports dual band operation.

            2.4GHz is a section of the ISM band (industrial / scientific / medical frequency band, Industrial Scientific and Medical Band), and all countries are open, so many wireless technologies use this band (mainly microwave oven, Bluetooth and ZigBee, WiFi, garage door controllers, cordless phones, line free mouse, and some wireless home appliances).

            5GHz: China has opened two bands of 5.8GHz and 5.1GHz.

            5.8GHz (5.725~5.850GHz) frequency band:

            The 5 subchannels (149153157161165) which are not interfered with each other belong to the ISM band.

            5.1GHz (5.150~5.350) frequency band:

            It contains 8 mutually independent subchannels (36,40,44,48,52,56,60,64).

            Application protocol: 802.11a/n/ac, where 801.11n supports dual band operation.





            2) rate:

            Correlation rate and actual throughput (described below are related rates of WiFi).

            In actual transmission, the maximum effective throughput is only 50% of the associated rate due to the short message of the Beacon frame (beacon), the transmission delay, the competitive avoidance and so on.

            When the 2 and 3 devices send the data at the maximum rate of correlation, the utilization rate of the entire wireless network is the highest; the number of equipment increases again, and the overall throughput of the wireless network will decline rapidly.

            802.11: only 1, 2Mbps, two rates.

            802.11b: a total of four rates, increase 5.5, 11Mbps two rates, downward compatibility 802.11.

            802.11a/g: supports eight, 6, 9, 12, 18, 24, 36, 48 and 54Mbps rates.

            802.11g is down compatible with 802.11b, with a total of 12 rates.





            3) bandwidth:

            Channel binding (Channel Bonding)

            802.11n starts to introduce, means multiplying the bandwidth, and actually occupying adjacent channels in practical operation.

            802.11n supports two kinds of bandwidth of 40MHz and 20MHz.

            802.11ac supports higher 80MHz and 160MHz bandwidth.





            4) quantity of space flow

            MIMO (more than Multiple-Input Multiple-Output)

            MIMO uses space multiplexing technology to divide the data into multiple parallel data streams and transmit them through multiple antennas. In order to avoid the disagreement of the cut signals, multiple antennas are also received at the receiving end. The separate signals are recombined according to the factors of time difference to restore the original data. Transmission efficiency is directly proportional to the number of data substreams (spatial flows).

            The 802.11n protocol supports up to four space streams.

            The 802.11ac protocol supports up to eight space streams.

            The biggest feature of 802.11ac WAVE2 is to support MU-MIMO (multiuser input and output, Multi-User Multiple-Input Multiple-Output), which can further improve the utilization of wireless network.





            5) MU-MIMO

            MU-MIMO (multiuser input output, Multi-User Multiple-Input Multiple-Output) technology implementation description:

            Uplink MU-MIMO: different terminals use the same time-frequency resource for uplink transmission. (no need to change the terminal side. The device side needs to identify the terminals and isolate them, so as to avoid interference).

            Downlink MU-MIMO: devices use the same time-frequency resources to transmit downwards to different terminals. (terminal side by eliminating / zeroing (Zero Forcing) algorithm to separate data streams that are sent to different terminals, or by using the method of BF (Beam forming) on the device side, to separate the data streams of different users in advance, thus simplifying the operation of the device side.





            WiFi technology is deficient.



            Advantages of WiFi Technology

            1) network coverage is large and mobile is convenient.

            WiFi's hotspot covers a large area, up to 200 meters in diameter, which is expanding as technology advances.

            In the hot coverage and product of WiFi, if the number of users changes, it is only necessary to increase or reduce the mobile terminal, that is, to increase and decrease the wireless access point, which is very convenient and fast.

            The WiFi connection point network is different from the wired network. It does not depend on the physical wired backbone. The user can move freely within the coverage of its hot spot without breaking the connection, and can set up a network at any time according to the need. If necessary, it can be used.






            ?


            亚洲日韩精品欧美一区二区_无码日韩免费看A片_av影音先锋_性欧美高清短视频免费