Thank you Nakul, for the overview. I think I learned so much about how wireless communication fundamentally work. I do have a couple of questions though, hopefully you can help me to clarify. Sure. I think the first will be, when you talk about interference or the noise. What would be the example for it? Would it be like in the urban environment? Let's say in the buildings or you're talking about more like a natural factors, like the trees, mountains and foliage etc. Good question. Just to reemphasize, noise and interference are some of the impediments, as we discussed, that degrade the quality of your wireless signal. Noise is mostly natural in it's source in that, just like us human beings hear ambient noise all the time, like a car passing by or rustling of the leaves. Most electronic devices also hear some electrical or thermal noise. That electrical or thermal noise is the electronic version of ambient noise that us human beings hear. Noise is natural in its origin, mostly, but it doesn't quite originate from the trees or buildings as far as those electronic devices are concerned. That noise in a simplistic manner can be considered to be present in the wireless channel, the media, or the device itself. As far as interference is concerned, as we discussed, it is deliberate. That is, if someone else is trying to send a wireless signal at the same time and the same place that you're using or you're trying to use that wireless channel. Yes, that other transmission will interfere with your own intended transmission. That is the basic difference between noise and interference. Now, as to your question whether trees and buildings might lead to noise or interference. Well, not exactly. Such obstacles, natural or man-made, tend to have certain other effects on the wireless signal. Effects such as blocking, shadowing, reflection, refractions, diffractions, etc. Let's look at those one by one because they do have certain merit in wireless engineers mind. So what is blocking? It's pretty easy to understand. Just like visible light cannot pass through an opaque surface. Electromagnetic signals, which are wireless signals have difficulty passing through certain objects to varying degrees. Through some objects, they can pass, let's say, 50 percent of their strength. Through some other objects, they may be able to pass only 2-5 percent of their strength. Through some other objects, they may not be able to pass any strength at all. That is essentially blocking and more importantly, concrete or brick buildings have a big impact on the blocking that I just mentioned. Other factors such as reflections, are also quite important. When a wireless signal or any electromagnetic signal in general, hit some metallic surface, a lot of its energy is reflected back in a specific direction, that is reflection. Just like how visible light reflects from the surface of a smooth mirror. Reflections tend to be problematic, but wireless engineers over the years, have devised certain techniques that can actually take advantage of those reflections. When we talk about MIMO, in a little bit, or if the audience is already aware of MIMO to a certain extent. They will know that MIMO is one of those technologies that actually takes at one page of those reflections. So to answer your question, noise and interference, noise that is naturally present because of the nature of the medium, interference is deliberate. Other natural or man-made objects like trees, buildings, cars, etc, cause certain other impediments to the wireless signal. Impediments like blockage, or shadowing, or reflection, refraction, diffraction, etc. That is how you can separate multiple phenomenon. I see. I think you've brought up a really important point. You're talking about different electronic devices, and they're operating different channels, different frequencies. How does that work, if I have my cell phone and there's a Wi-Fi router or the smart home devices around me. How does the channel and frequency work? Then how will that avoid or cause interference? Another good question. So what channel a wireless device uses is mainly determined by two factors. What kind of device it is, and what kind of service it is offering. For example, our old FM radios, they work in one band. The Bluetooth devices that you may have, they work in yet another band. Let's say the satellite TV and radio, they work in an altogether different band. International agencies and to certain extent, local, national regulators like FCC in the United States make that decision. But to a certain extent, if not to the extreme extent about what kind of devices will operate in what kind of spectrum. So to pick on your example about a cell phone versus Wi-Fi devices, they inherently work in two different bands. For example, in North America, cellphones typically work under or around two gigahertz of frequency, whereas Wi-Fi or Bluetooth devices, can either work in around 2.4 gigahertz of frequency, or around five gigahertz of frequency. To answer your question at the high level, because those devices fundamentally operate in two different bands or two different parts of the frequency spectrum. It is fair to say that by default, they won't interfere with each other. You don't have to be worried about your cell phone versus your Wi-Fi devices. That, however, brings me to raise another question that even you may have thought of already. That hey, if my cell phone and Wi-Fi devices won't interfere with each other, that's fine. But how about multiple Wi-Fi devices that I have? Will they interfere with each other, if not the cellular phone? Well, if you don't do anything, they might interfere with each other. But the international agencies are the standardization bodies, as we engineers call them. They have put a lot of thought into that problem already, and they have device certain sophisticated sets of algorithms that prevent these Wi-Fi devices from interfering with each other, even though they operate in the same frequency band. Technicalities can get pretty gruesome. But to give you one simple example, imagine a classroom full of students. Let's say, the teacher say something, and multiple students have questions at the same time. But you won't see all of them asking their questions all at the same time. They will most likely raise their hands and they will ask their questions one at a time, so that their questions don't interfere with each other. The multiple Wi-Fi devices that you may have in your house work in pretty much the similar manner. I'm simplifying things here, but they work in a similar manner that whenever a Wi-Fi device, like your laptop, wants to talk to the network, it raises its proverbial high in technological talk saying that, I want to talk to the network. If there is no other device that is looking to talk to the network at the same time. That is when your laptop can communicate with the network. That is how all the devices in your house take turn talking to your Wi-Fi router, making sure that even though they operate in the same frequency band, they don't interfere with each other. International standardization bodies have put a great deal of effort in codifying and standardizing those interference mitigation algorithms.
