What is an Air Node? How do you build a Cell Network?

We are going to be building 4G LTE networks. Eventually we may move on to 5G but for now the towers and network communication protocols we are going to use is 4G Long Term Evolution or LTE or eUTRA if you are so inclined. As we are building these networks we are going to provide this resource for people to learn how these Air Nodes work and how to build a comprehensive Air Node Network. Obviously this is going to be as brief and as dense and useful as possible. This is meant for people who want to build decentralized World Mobile Air Node Networks. I will cover the basics of Electromagnetic Waves, Network Hardware, and Network Hardware Topology as well as applying this to some of the actual air node antennas we have tested. 

Electromagnetic Wave Basics

The-electromagnetic-spec

We are going to enter a world where everything is RF or radio frequencies. Everything you see, everything on your phone or going across a network, the way your computer computes etc is an Electromagnetic wave. We are going to generally be dealing with waves well under the 300MHz that can be considered the top of the radio frequency spectrum when talking about Air Nodes. We will be using Microwave transmissions for line of sight cell connections that will help us spread signal where there are no physical fiber optic lines. The networks we are going to build will probably have some/many 5-60 GHz point to point microwave antennas that connect Cells to each other. The rest are going to be CBRS 3550-3660 MHz, cell 600/2300, 900/1800, 800/1900 MHz and other cell bands for tower to user session management. And 5G phones will not kill you any more than light from the sun will kill you. It is just another frequency slightly closer to the microwave range. On the other hand don’t walk in front of microwave antennas. Microwave ovens became a thing because someone in the Navy found out they can cook stuff. We learn things the hard way in the Armed Forces. The difference between 3G, 4G and 5G is mostly phase modulation and amplitude math described below.

Signal To Noise Ratio

One thing to keep in mind while i show some pretty and clean pictures of wave signals below is to know that the real world is noisy. There is RF garbage going everywhere. All of the nice pictures I show below are going to look a lot more like these pictures to the left in the real world. Our Air Nodes true effort is to find OUR signal while other networks are trying to do their thing and that prepper in Montana is telling everyone on his HAM radio that the Russians are coming. Our antenna’s biggest enemy is other antenna’s in our network because they are on the same frequencies. So keep EM Noise in mind as we continue 

Amplitude, Frequency, and Phase

The three basic variables you need to keep track of when dealing with RF is Amplitude, Frequency, and Phase. Every electromagnetic wave has a Height and a Width and travels a complete cycle. We tend to display wavelengths as 2 dimensional lines bouncing between a top and bottom, but it is of course more complicated than that.  We can start the cycle at a different point in the phase but the cycle needs to complete each time. Timing is of course incredibly important for all of this and all of our signals need to stay on frequency. 

Amplitude Modulation refers to the height if an EM Wave. The simplest method of transferring information is Amplitude modulation. Because the amplitude of an EM wave is the easiest thing to change this is not the highest quality signal or a good way to transfer large blocks of data.

Frequency Modulation works by changing the frequency within a channel. FM Radio stations end in an Odd number because each station uses the “Center” channel +/- .1 so 107.9 is actually 107.8-108 giving the radio station “space” to modulate the frequency. This is OK for music and voice but changing the length of a cycle drastically complicates the math in filtering for signal so it is not good for data transmission.

freq-modulation

Phase Modulation and Analog vs. Digital

The above modulations are considered Analog Signals. This is where we start getting into Digital Signals.  We can use amplitude or frequency to encode digital signals into EM Waves. 

But this is where things start to get a little out of hand. The final variable we will cover is Phase Modulation. The “energy” of your wavelength determines where it is with respect to it’s phase. Energy isn’t the right word here but go with it. We can transfer digital signals by modulating the phase. An up-down-up is one type of phase. Down-up-down is another. We could assign these to 1 and 0. Same EM Wave, different “start” point.

But stopping there would be silly. We have to hold the frequency static so that we can have more channels and better noise filtering. But if you expand the idea of phases out to it’s practical limit you can have 8 phases. Combine this with Amplitude modification and you can easily get to 16 phase-amp combinations like so. Modern networks range from 16 bit to 1024+ combinations. The balance is between transmit rate and error correction. As frequency and amplitude modulation gets higher your antenna and software have to get better to filter the signal out of the noise. But higher frequency also means faster data transmission.  

Network Topology

Network Topology generally refers to the layout and design of a Network. Networks are generally divided into Cells. A cell will describe an area covered by an antenna/controller that is receiving data from and transmitting data to users. In the beginning they were all big towers and maps were all hexagons. Now not so much.  Generally you will see several vertical aligned antennas at the top  and some little round antennas underneath them on a typical cell tower. Modern Macro Cell towers will also generally be divided into 3 120 degree pie slices.  There are more micro and pico cells now which is what most people looking at Air Nodes are interested in, but this gives us a good frame of reference.

When you are talking about a cell network these are the basic components. There will be antennas which are usually obvious. There will be one or more base stations that generate the EM waves labeled as the Remote Radio Unit right. The Baseband Unit is a glorified router. Finally there will be some way to connect to the Core Network over the internet over high speed back haul. This will be an actual ONT hookup to the internet for a gateway eNode, or one of the little round line of sight microwave frequency antennas mentioned/pictured above for a regular eNode to connect to a gateway eNode.

Basic EM Wave Properties

Our transmitter antennas are a lot like a drum. But instead of hitting hide/plastic stretched around a drum with a stick the Exciter is spewing electrons into a specifically shaped bunch of metal with specific conductivity characteristics at specific frequencies. So when you are “pointing” your antenna it is a lot like pointing the noise out of a drum. Sometimes we can shape our antenna so it is more like a trumpet and will go farther in one particular direction. You will still be able to hear it behind you and EM Waves will make you believe in magic.  

What comes out is your signal. On the other end will be the receivers. In our case cell phones. So the real magic is when the cell phone is able to pick our signal out of everything else being broadcast and put that cat video you were dying to see on your phone. Meow!

Phones are Small Antennas with Stuff

So all of these communications are 2 way and your phone does all of the same things with signal and antenna the tower does. Additionally your phone monitors all of the channels on our band and most likely bands of other carriers you can roam with. Obviously cell phones are much smaller and operate at much lower power. This is why there are cells. You can have a 1000W tower that can reach to the horizon with a T1 internet connection, but the limiting factor will always be the mobile hand unit running at 2-2.5W. There are ways around this but keep this in mind as we get into designing a network.

Networks are going to use Cell Radio Frequencies for User Sessions. These are sessions of communications between a mobile user and a tower. Single user bandwidth is possible over these frequencies and the lower frequencies are more tolerant of physical obstructions. As frequencies get higher you can transmit more data but trees and buildings and terrain become more of an issue. 

Radio vs. Microwave

 

And there are cells that have no Fiber/Internet connection. What we can do in this situation is handle the User sessions with a standard air node, but instead of connecting the eNode to the internet we pipe the user session data between two Microwave Antennas and connect to a cell with a direct connection to the Core Network.

We are going to be building complete Air Node networks. There are several common scenarios  in network design. The easiest situation is standing up a big tower on top of a direct ONT hookup to the internet and a straight pipe to the Core Network. But there are situations like large buildings whose walls block RF. There are remote areas with no high speed internet connections for miles. There are towns and event venues that have thousands of people show up and leave. Populated downtown areas will have hundreds of users per square mile. Highways with fast moving vehicles will have users constantly hopping between towers. Terms you will get familiar with are context switching and cell to cell hand off which take a lot of processing power.  The big companies are into maximizing profit. But even if they weren’t rat bastards this is not simple. Local communities are much more interested in doing a good job. Decentralization is just better. 

History of Mobile Network Technologies.