wireless router knowledge mistake!Interpretation of the antenna number and signal strength of the relationship between the
antenna routing is better?
An antenna coverage is wider, the more the more the stronger the signal, the routing is better in short antenna "Feel very Common sense "Friends can continue to look down the body.As you read antenna number and the relationship between signal strength!
first of all, you should also be noticed that the older generation wireless router antenna will not more than one root, here The older generation "Refers to the 802.11 n agreement before 802.11 a/b/g routing, old 54 m products only an antenna.So, 802.11 n is apparently a watershed, and since then the antenna is no longer only one lone root (1 t1r 150 m is an exception), that what is going on?Here we are after a 11 n agreement to get the specific application of multi-antenna technology, is also a very important in the field of wireless communications technology MIMO (Multiple Input Multiple Output, much more than)
first to see, for example, some people say that, why I bought a latest 3 antenna support ac 802.11 protocol of wireless router, the signal intensity, the coverage even didn't speed up?The antenna is not enough?To tell you, 300 root also useless, check your use of receiving terminal does not support AC agreement.Such as you use the iPhone 3, this cell phone can support only 11 a/b/g even far from 11 n, so even if you give this it down with a few antennas also useless.How to solve?Equipped with AC adapter or in terminal, in short antenna is useless.
why say so?First of all, the application of wi-fi is indoor environment, we often use the 802.11 series of agreement is set up for this condition.Because the transmitter to the receiver between all kinds of obstacles, when to send and receive almost non-existent direct signal.That how to do?The idea is known as multipath transmission, also called multipath effect.Multipath, literally also is easy to understand, is to increase the transmission path.Since
so the question comes, is multipath, transmission distance has long have short, and some may be reflected from the table, some may be through walls, these carry the same information but with different phase of the signal and eventually gathered together on the receiving end.Modern communication is store-and-forward packet switching, also called packet switching, transmission is code (Symbol).Due to disorder of different transmission delay, will cause the intersymbol interference (ISI) (InterSymbolInterference).In order to avoid the ISI, the bandwidth of the communication must be less than can tolerate delay countdown.For 802.11
a/b/g 20 MHZ bandwidth, the maximum delay of 50 ns, multipath transmission radius under the condition of no ISI is 15 m.In IEEE802.11 agreement we can see that the value of maximum range is 35 m, this is the agreement and a variety of means such as error retransmission guarantee communication, is not to say that there is a little ISI was completely unable to work.So you will find that for 802.11 a/b/g agreement, even if there was no sense in adding more antennas.Instead of assuming that the antenna can work at the same time, can make the multipath effect.All in all,
is the scope of wireless router to launch the IEEE802.11 protocol, rather than to simply look at antenna.Say so many,
single antenna routing, double antenna routing, three line four lines, and even more have what differentiation?Are, but for actual use in the process of impact is not big, this includes the signal coverage, signal strength, antenna speed even more nonsense.Despite the already very rare single antenna, & the rest of the other;Multiple antenna "All just realize MIMO technology Medium "Or rather, Tools ", the difference is that the use of different architecture: common dual antenna products mainly use t2r 1 or 2 t2r, three antenna products is used in 2 or 3 t3r t3r.
in theory, increase the quantity of the antenna will reduce coverage blind spots, but we through a lot of evaluation, confirmed that the difference in the average family environment completely negligible.And, like built-in antenna can be external, three antenna coverage than double antenna is not alone, in the end product quality is also an important factor.As for the signal strength and "Through walls "Depends on the transmission power, this thing ministry made provisions, shall not be higher than 20 DBM (100 mw), The more the more antenna signal "Also falls.The last conclusion is that, as long as the route adopted effective MIMO technology, do not need to care about antenna number.
the next page we will further understand the magic of MIMO technology.
search all kinds of IEEE802.11 wikipedia data entry, we can read, since 802.11 n, data transfer rate or the carrying amount of data that has a lot of improvement.First, 802.11 n had 40 MHZ model, according to the previous theory, however, the scope of its launch should therefore reduced by half, but in fact data bolster doubled (70 m), how is that?
this will benefit from the MIMO technology, just now, we discuss a variety of means is to combat severe multipath environment, but the multipath is there any good?In fact, also based on multipath MIMO, we call it space diversity.There are many kinds of technical means, the application of multiple antennas here introduces two: Beamforming (Beamforming) and space-time block codes (mainly introduces Alamouti & # 39;Scode).The advantage of the two technologies is don't need multiple receive antennas.Especially the Alamouti code, even without channel information, using mathematical operations can use two antennas to achieve 3 db gain, nice right.
without the need for multiple receive antennas is that not all the advantages of the device can be fitted with multiple antennas.In order to avoid the side lobe radiation (antenna pattern, the radiation beam is called main lobe largest, next to the main lobe of small beam called sidelobe), meet the space sampling theorem, to send signals of half wavelength as a general physical antenna spacing.From the GSM signal 1.8 GHz and 1.8 GHz or 2.4 GHz wi-fi signal, we temporarily take 2 GHz is easy to calculate, half wavelength is 7.5 cm.So, we see most of the distance from the antenna on a router so that it is, therefore, it is hard to multiple antennas installed on mobile phones.Borrow
Beamforming (Beamforming) : is produced by multiple antenna with a directional beam, the energy is concentrated in the want to the direction of the transfer, increase the quality of signal transmission, and to reduce interference with other users.We can simple understand it in general antenna directivity: assume that all power of directional antenna is 1, only the range of 180 degrees of directional antenna power can reach 2.So we can use four 90 - degree power antenna quadrupled in theory.Beamforming is another pattern through channel estimation azimuth at the receiving end, then have directed against that point emission, improve the transmission power (similar to the condensing flashlight, the smaller the range, the brighter the light).Smart antenna technology is established on the basis of the shape of the beam.
space-time Block codes (Space - Time Block Code, namely STBC) : in a multiple antennas on different Time to send information to improve data reliability.Alamouti code is space-time block code in one of the most simple.Two yards, in order to transmit d1d2 separately send in the two antennas 1, 2 d1, d2 * and d2 and d1 *.Due to multipath, we assume that the two antennas channel h1h2 respectively, so the information for the first time the receiver receives r1 = d1h1 + d2h2, after receiving the information of r2 = - h1 + d1 d2 * * h2.Received the 2 d square if multiplied by the channel, can get the information of d1d2.Look not to understand it doesn't matter, anyhow it is Alamouti find a set of orthogonal code rate for 2 ×2 matrix, in this way on the two antennas can launch each other;An antenna can be used to receive, through mathematical method of sending a message to get in the future.
other MIMO, may better understand on the concepts, such as two transmitting antenna t1t2 respectively on two receiving antenna r1r2 launch, then the equivalent of two people working at the same time, speed up 2 times, and so on.But actual implementation on the one hand require multiple receive antennas on hardware, on the other hand need to channel estimation algorithms such as communication, it is very complicated, and time-consuming and the calculation of the hardware.
about the above two kinds of technology is, in fact, MISO (Multiple Input Single Output) method, is also to prove from another aspect, the antenna does not mean that they can work together.100 years ago, more people will know that the antenna, the better the bigger the better, but the genius of the Alamouti code 1998 years to be brought up much antenna technology of 802.11 n agreement in 2009 before application.
20 years ago, people use OFDM (Orthogonal Frequency Division Multiplexing, namely Orthogonal Frequency Division Multiplexing, a multi-carrier modulation technique) against caused by city or indoor obstacles too much multipath fading, and now we have started to improve the quality of communication with multipath.This is the development of the technology by leaps and bounds, rather than a simple "Take it for granted throughout the &;Can be achieved.
is written in the last
mimo itself is a time-varying, not smooth in the system.Research on MIMO, is a worldwide issue, still have a lot of questions left, the same problem even also can appear different academic.However, for general consumers don't have to dig in, saw the beginning we speak Myth ", know routing antenna is a Tools ", double antenna to ordinary families, when the choose and buy to see the product specifications, don't be misled by the businessman.related:
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