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<blockquote>Around the Wi-Fi signal and transmitting and receiving circulating myths and users will then wonder why the connection is so slow. Come with us to look into the mysteries of the spread of Wi-Fi signal. </blockquote> <div> <h3>Related  Article....</h3> </div> <div> <ul> <li>Wi-Fi standards, channel settings, expand the scope of</li> <li>Antennas and their settings, distortion and loss of signal measurements</li> </ul> </div> Wireless network Wi-Fi is already virtually in every home with a laptop or smart phone - enough to buy a Wi-Fi router. Coverage of quality wireless throughout the house so that every corner not only the signal but also high speed connection no longer requires deep technical knowledge. The same is true of outdoor Wi-Fi solutions. You must be aware of all the standards used, the Wi-Fi channels in 2.4 GHz and 5 GHz band, the antennas, sensitivity of the device attenuation and reflections environments and technologies such as MIMO and Beam forming. [caption id="" align="alignnone" width="480"]<img alt="wifi router" height="320" src="http://zive.v.mfstatic.cz/GetThumbNail.aspx?id_file=270696575&width=480&height=320&q=100" width="480" /> wifi router[/caption] <h3>From hands off of obsolete standards</h3> Standards Wi-Fi are numerous, from the first 802.11 (no letter) to the latest 802.11ac and 802.11ad. The 802.11 and 802.11b (11 Mb / s) however you can forget it. They are obsolete, in retrospect quite unsatisfactory and lots of equipment it is not supported. The great expansion of Wi-Fi in our care to 802.11 g with a signal rate of up to 54 Mb / sCommunicates only in 2.4 GHz band and uses OFDM modulation or older DSSS for compatibility with 802.11b. It is this compatibility but may cause a reduction in throughput of the entire network if it jumped in the old device with 802.11b. But even the 802.11g standard is now obsolete, and not just because of the low speed, but because it does not includes support WPA2 encryption - uses the old broken by WEP. Moreover, it may be the only reason for the reduction 802.11g throughput across Wi-Fi networks based on 802.11n. Physical (sync) versus real (TCP) speed: [caption id="" align="alignnone" width="604"]<img alt="wifi router" height="374" src="http://i62.tinypic.com/2620cco.jpg" width="604" /> wifi router[/caption] Due to the limited frequency band at 2.4 GHz was still 802.11a standard, which is identical to 802.11g, but communication takes place in the 5GHz band. He has used strictly OFDM modulation has a greater optical power, because it was used to great distances. I already 802.11a standard is obsolete but due to the low maximum speed of 54 Mb / s, the same as for 802.11g. <h3>Require full 802.11n MIMO</h3> Completely most widespread today 802.11n, which can communicate in both bands (2.4 and 5 GHz). By adjusting the physical and data link layers and the introduction of technology MIMO (multipath propagation) brings real speed of more than 100 Mb / s However, there are many routers and even laptops with only one antenna (1T1R - one antenna at the transmitter, the receiver one), so they can not take advantage of MIMO technology, which theoretical speed drops to 150 Mb / s (actually 5-6 megabytes / s). This lightweight standard tends nickname 802.11n-lite or N150 and I suggest you avoid it. Achieve physical speed of 150 Mb / s belongs in noisy band of 2.4 GHz mostly to the realm of sci-fi, as it is the value at 40 MHz channel width. Often you get from such a Wi-Fi router a channel bandwidth of 20 MHz and a natural rate drops to 72 Mb / s (actually 2-3 megabytes / s). MIMO technology provides a significant increase in speed due to the fact that the transmission of multiple signals and multiple antennas at the receiver side also received multiple antennas. The antenna must be rotated in different ways to go other routes signals and do not interfere with each other. Finished with stacked together and the data is transmitted, resulting in up to 2 × (2T2R), 3 × (3T3R) or 4 × (4T4R) faster than the n-lite. The problem of course is cast other channels. <h3>Great attention to the channels</h3> In the 2.4 GHz band in Europe a total of thirteen channels and frequencies from 2.401 to 2.483 GHz, which means that there is a total bandwidth of only 82 MHz. Channels overlap, so the result is that there are actually only three non-overlapping channels (for a bandwidth of 20 MHz) - 1, 6 and 11 (2.401 to 2.423 GHz, 2.426 to 2.448 GHz and 2.451 to 2.473 GHz). In the 2.4 GHz band and can operate up to three N150 WiFi routers without interfering with each other, all but only with 20MHz bandwidth, ie the physical speed of 72 Mb / s If you would like a bandwidth of 40 MHz (the natural rate of 150 Mb / s), you can only use channels 1 and 9 when two routers together, and even though the band will slightly overlap. <div> <div> <blockquote> In the 2.4 GHz band, there are only three 20MHz channels which do not overlap and thus do not interfere.In the 5GHz there are nineteen </blockquote> </div> </div> Another slightly overlapping channels with a width of 40 MHz is the reason why even in the ideal case where the 2.4 GHz band is not interference, it will never reach full physical speed of 300 Mb / s Two streams transmitted by two antennas will interfere with each other slightly.Therefore, the N300 fully used up in the 5GHz band, where there is much greater bandwidth.Nevertheless, the N300 with a bandwidth of 20 MHz to 2.4 GHz band much more sense than the N150 with a bandwidth of 40 MHz. The reason is very strong interference (Bluetooth, wireless adapters, all running at 2.4 GHz) and other Wi-Fi networks. While the two streams is not a problem 20MHz transfer (physical speed of 150 Mb / s), one problem is 40MHz. So if you want a fast Wi-Fi, avoid not only jednostreamovým Wi-Fi routers, but also Wi-Fi cards in laptops, phones and other devices. <blockquote>Frequency ranges of channels in the 2.4 GHz band (2401 až 2483 MHz) , only three are exceeding 20MHz channels (1, 6 and 11), a total bandwidth of only 82 MHz. </blockquote> [caption id="" align="alignnone" width="620"]<img alt="wifi" height="345" src="http://i59.tinypic.com/vfcowy.jpg" width="620" /> wifi[/caption] While in the 2.4 GHz frequency range is only 82 MHz, at 5 GHz is higher 520 MHz (from 5.18 to 5.70 GHz). There is a total of nineteen channels with a width of 20 MHz, which have no overlap. This fact, together with minimal interference by other devices has resulted in a truly high-speed data transmission. U 5GHz networks, however, there is a problem with a smaller range, which make obstacles more of a problem than the 2.4 GHz network. With a width of 40 MHz channel in the 5 GHz band can communicate simultaneously nine devices without interference. The result is a total of four in 2T2R MIMO (N300) or three at 3T3R MIMO (N450). With the new 802.11ac standard is already a channel width of 80 MHz (the natural rate of 433 Mb / s for a single stream), so in three streams (3T3R) shall possess nearly half the 5GHz band. Mutually disturbing Wi-Fi 802.11ac routers with the physical speed of 1300 Mb / s and can be next to each other only two. In the future, it is to be expected that the 5 GHz band is much occupied. Indeed, not only increase the speed requirements, but also the number of users who use the Wi-Fi. <h3>How to extend coverage</h3> Methods to extend the coverage of Wi-Fi networks, are several. The simplest is to insert into the network Wi-Fi Universal Repeater (Universal Repeater). He does nothing else than to take Wi-Fi signal on the same channel and sends it on. Must be the same as it has two radio interfaces. The result is approximately half the rate for this repeater, despite the fact that you have to put a repeater of course where there is a strong signal from the source, otherwise it will be much lower rate. [caption id="" align="alignnone" width="301"]<img alt="wifi" height="200" src="http://zive.v.mfstatic.cz/GetThumbNail.aspx?id_file=342838237&width=301&height=200&q=100" width="301" /> wifi[/caption] Another option is a system WDS (Wireless Distribution System). After the deployment of Wi-Fi routers is difficult to wirelessly connect, but again will be for each router through degraded at half, everything happens on the same channel. The only reasonable solution to wireless WDS is used for the backbone network 5GHz band, but again we face the problem that you have to use a lot of network elements (routers must be in place a strong signal of the previous ones). Like so WDS repeater is better suited at covering space. The real full Wi-Fi system, which also covers a large building with several floors of a high-speed wireless networks, interconnection is Wi-Fi router AP or cable or other type of network (eg powerline). In the case of building such a network but you must be careful not to each other Wi-Fi routers do not interrupt or put each on a different channel - the best alternate channels 1, 6 and 11 at 2.4 GHz network and a channel width of 20 MHz. If the environment does not change for channels 1, 5, 9 and 13, with minimal overlap.