Basics of Antennas and Beamforming - Massive MIMO Networks

in this video I will tell you about the basics of antennas and beamforming so the first thing to know about an antenna is that it contains a radiating elements just as a light bulb that is radiating electromagnetic waves in a particular direction so in this case it will rate it in this direction and it's the same thing with the typical radiating element in an antenna if you would like the radiation to be more directive pointing in a particular direction towards you then you can put multiple radiating elements next to each other and feed them with the same signal we still call this one antenna but the signal will become more directive and with two rated and elements you get twice of the energy going forward and less energy going out directions we're using the same amount of energy still and these two times we call it three decibels similarly if you have four rated elements and you feed it with the same signal you still have one antenna but you get four times the amount of energy going forward we call it six decibel of array gain the problem with making a more directive signal is that you only benefit right in front of it so if you know what the users going to be you can make sure that you get this much stronger signal that we call an array gain towards its user but if the user is at different locations just as you will move around the light emitted from a flashlight in order to see a large area you need to do the same thing with this beam that you're forming in order to reach your so like the red user in this case here and then you can use the same number for rating elements for example but you need to feed them with different signals in order to create constructive interference in the direction of interest so you can send the beam if I take a direction not a beam in that direction and hopefully you send in direction where the user is and in order to do that you can send the same signal up with different faces and that will then create a constructive interference in a particular direction in addition to that you can also adapt the amplitudes to create other types of beams we call these different rating elements and antenna so the number of antennas is equal to the number image that you're having and if you have two antennas as you can see here you can see that you can form a strong beam in a particular direction but you will get some leakage in other directions as well which we call side lobes we have the main lobe pointing direction of interest and side lobes not directions and if you are then having four rating elements you and you create one antenna each one of them you get a more directive signal in the vertical direction with less side lobes now directions and you can do something in between meaning that it takes for rayvin elements you map them two and two to become two different antennas and you feed each one of them with the same signal in one pair but you are adjusting the face between the first two and second two in that way you can steer beams in different directions but you will not have the same flexibility as before in particular you can get a narrow beam pointing in a particular action but you will also get additional side lobes that could be quite large pointing in a directions still this is something that is used in real systems in particularly when you are putting up a base station array on the rooftop then you can put together ratin elements that are adjacent to each other and feed them with the same signal and still used to send a beam downward because even if you get a signal going up first as well you don't really care about that because you use this won't be later so it won't create any unnecessary interference another important thing with having multiple antennas is that you can do which is called spatial division multiple access or spatial multiplexing that's two names for the same thing and that means that you send multiple beams at the same time it could be to the same user but in particular is of interest to send it to different users that want to access your system at the same time chika-san blue signal in this direction a red signal in this direction and then different users in different directions can receive these ones and since the amount of energy you can radiate from your radiation elements is limited you need to share them between them so instead of sending one strong beam here you send one half of the beam here half of the beam here for example and the more rating elements the more directive the signals are and therefore you can then send these signals to the users with less and less interference between them and you can multiplex as many signals as you have antennas so with four antennas you can choose between sending one strong beam to weaker beams or four even weaker beams however these four beams will still be as strong as if you only had one greater than elements to start with the don't listen to one signal when you have many radiation elements people can start to say well it will be too expensive to feed each one of them with an independent signal that you generate and why don't we send the same signal to each of them and just phase-shifted at the Raven element this is called a phased array and it's an old concept and you can use it very nicely to steer beams in different angular directions but you need to assign the same amplitude to each of the Raven elements and you can only send one beam at a time there is a hybrid beam forming approach where you try to do the same thing with multiple beams where you have fewer beams and radiating elements here you can see an example of the problem with using these type of things I space the race because this is a user where there is no particular path that leads the best to this user there are two different drum directions that we can send the beams in to bounce different objects and get the signal to reach you sir and if you use the faced array you need to select only one of them and if you have all the flexibility of beam forming by having four antennas in this case one input to each of the Rays and elements you can send a beam that points into both of these directions and you put in that way be able to get twice the energy being reached at its user because you're using multiple paths still people might be arguing well yeah we need to sacrifice this capability in order to bring down the price but this is actually a bit of a misunderstanding because there are already at commercial solutions to do this kind of thing so here you see a figure of a 64 antenna base station that have already been deployed in the US and it contains 100 print creating elements which means that each antenna is made about two different radiation elements and to understand what actually going on here we need to talk about polarization so electromagnetic wave if you can have different polarizations like that or like this and each antenna is only sensitive to one type of polarization so there's a risk that you can get signals of a polarization that you cannot detect any antenna unless you have two orthogonal types of polarization so for that reason the base station array contains 64 rated in elements a one polarization and 64 other radiating elements with the other polarization and then the use of device can be rotated in any way you like and we call this big arrays with 64 times massive MIMO so if you would like to learn more about the massive MIMO you can read my book massive Lima networks you can download a free PDF of it at massimo book comm in particular section 7 provides the theoretical details of antennas beam properties array design polarization and other things that i've covered in this video

Channel: Wireless Future

Views: 191,483

Keywords: antennas, beamforming, radiating element, MIMO, Massive MIMO, Massive MIMO Networks, Emil Björnson

Id: xGkyZw98Tug

Length: 7min 46sec (466 seconds)

Published: Wed Nov 28 2018