people when the choose and buy a wireless router will have a question, whether wireless routers 1, 2, or 3 antenna wireless signal is better?Most of the friends in the choose and buy wireless router will only be judged by the number and prices of wireless router antenna signal amplitude of the wireless router, wireless router on earth is the more antenna signal is better?A wireless router, what is the difference between second and third antennas?Small make up to sort out some information to share with you.One, two, three,
wireless router what is the difference between antennas?
mimo (much more), that is, multiple antenna technology from the agreement only after some 802.11 n, 802.11 a, b, g.That is to say, first of all, the old router (802.11 n) before never has more than one antenna.So you bought a new 3 antenna support 802.11 ac (protocol) latest router, if your device is old products, such as supporting only 802.11 a, b, g iphone3G, so it's a pity that so many antenna didn't make any sense to you.If unwilling to antenna launch at the same time, but will not have a good effect.
why do you say so?First of all wifi application is indoor environment.We often use the 802.11 series of agreement is set up for this condition.That is because there are a lot of buildings or obstacle, almost no direct signal between transmitter and receiver.We call this multipath transmission.That 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 gathered together on the receiver.We know that modern communication is packet switching, transmission is code (symbol).Due to different time delay described above, the intersymbol interference (ISI) (Intel symbol interference).In order to avoid the ISI, the bandwidth of the communication must be smaller 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 IEEE 802.11 protocol, we can see the largest scope 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.Scope of the launch of
that is to say, the router is agreement.Increased to 802.11 a, b, g, antenna doesn't make any sense.Instead of assuming that the antenna can work at the same time, can make the multipath effect.Multi-input multi-output (mimo) :
in wikipedia links (IEEE 802.11) we can find that from the beginning of the 802.11 n, the data has a lot of improvement, the first 802.11 n had 40 MHZ model, according to the theory, before the launch of his range should therefore reduced by half, and the data instead of ascending doubled (70 m), why?
thanks to the multi-antenna technology, just now, we discuss a variety of means is to combat severe multipath environment, but the multipath is there any good?In fact multi-antenna technology is based on multipath, 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;S code).The advantage of the two technologies is don't need multiple receive antennas.Especially the alamouti code, even without channel information, using mathematical operations with two antennas to achieve the 3 db gain, all teachers are full of praise!
don't need multiple receiving antenna has the advantage of, not all equipment can be fitted with multiple antennas.In order to avoid side lobe radiation, 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 wifi 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.Also for this reason, it is difficult for us to multiple antennas installed on mobile phones (not to mention samsung the 7 inch phone thank you).
1 Beamforming (Beamforming) :
borrow is produced by multiple antenna with a directional beam, the energy is focused on the transmission direction, increase the signal quality, and reduce the interference among 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 to determine the azimuth of receiver, and then have directed against that point emission, improve the transmission power.(similar to the condenser of the flashlight, the smaller the range, the brighter the light).But this model in which agreement application I isn't clear.Space-time block codes
2 STBC (Space—Time Block Code)
is a different moment send information on multiple antennas to improve the reliability of the data.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 respectively h1 h2, so for the first time receiving information 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 d1, d2 & hellip;& hellip;Well, don't seem to explain, can't don't have my notes, searched a circle also didn't find the right material.A word is Alamouti find a set of orthogonal code rate for a 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 t1 t2 respectively on two receiving antenna r1, r2 as 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 is actually the MISO method is also proved 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 technology against caused by city or indoor obstacles too much multipath fading, now we have started using multipath to improve the quality of communication.This is the development of the technology by leaps and bounds, rather than a simple "Take it for granted throughout the &;Can be achieved.Because don't have my notes in class, always feel some not too big hold.For Suppose to work on 802.11 a, b, g SISO model of three antenna router, can think 3 antenna has a larger gain?Throughout the &;And In between the two bridge model router equipment whether to download data from two router at the same time, how to synchronize?Throughout the &;Also be confused.After all, knowledge from books to actual application and a distance, so if there is any wrong place, welcome to point out mistakes.
: summarize the more antenna wireless router signal is better, but, good point is not to say that the wireless router antenna signal number, the more it ability of the launch of the wireless signal is multiplied, penetrating power, the better, in fact, many antenna signal wireless router is better than single antenna wireless router signal 10% to about 15%, is the performance of single antenna wireless router after a wall apart, it signals the rest one, while multiple antenna wireless router's wireless signal between the single and two, is generally not sensitive people almost can't feel their differences, unless you use WIFI signal test software can be very intuitive see differences in the wireless signal, and the double antenna compared with four antenna wireless router, wireless signal strength is almost the same.According to the results of the experiment test we summarize the opinion, wireless router antenna number for signal enhancement wouldn't help very much, only manufacturers use everyone's psychological effect to improve product marketing price.