How Cell Service Actually Works | Wendover Productions

0:00This is electromagnetic radiation. You can't see it, but it's there. In fact, it's everywhere, but here's a more relatable form. This is the color cyan. But more accurately, this is waves of electromagnetic radiation, oscillating at about 616,856,909,465,021 times per second. As they reach your eyes, light receptive cells translate the radiation into electric signals which travel to your brain and are generally perceived as the color that we collectively refer to as cyan. If we strip away our interpretation, though, the radiation scaled up about 100,000 times looks like this. The color cyan is waves of energy roughly 486 nanometers wide, but what happens if that width tightens? At 380 nanometers, our perception changes to this dark purple. Meanwhile, if it expands to a roomy 780 nanometers, our brains interpret the radiation as this shade of dark red. Essentially, as the wavelength changes, so too do the properties. So what happens if

1:06we change the wavelength more dramatically? Like tightening it by 100 times? Well, now the waves have much higher energy. They're much more powerful, so much so that they can actually pass through some less dense materials like fabric or human tissue, but they aren't quite strong enough to pass through denser materials like metal or bone. You can see where this is going. We refer to these wavelengths as X-rays and use their special properties to look inside bags at airport security and inside humans at the hospital. So what happens at the other end of the spectrum? What if, instead of the width of human DNA, the waves were the width of humans? Well, this is what we'd refer to as an ultra-high frequency radio wave. Its comparatively enormous wavelength allows it to travel over huge distances, pass through obstructions, and even bend around obstacles. All useful properties if you wanted to use electromagnetic radiation to, say, communicate. Of course, in order to convey information using a radio wave, we'd need a way to manipulate

2:08the radio wave that corresponds to the desired information. For this, there are options. To start with, there's the strength of the wave. We know that a blue light, for example, can be weak or strong, but no matter if it's weak or strong, it's still blue, and the fact that it's blue means that it's still fundamentally the same wavelength of electromagnetic radiation. The same principle applies up the spectrum with radio waves. They can be powerful, weak, or anywhere in between, and still be the same wavelength. In this context, we call that strength the amplitude. Therefore, we can transmit an audio signal, for example, by modifying that amplitude by a proportional amount. The receiver just needs to know how to interpret those amplitude modulations and translate them back to an audio signal. In the case of an AM radio station, the radio receiver only focuses on the radiation with a wavelength of 1119 feet or 341 meters long, for example, and it tracks the amplitude modulations to output the audio signal that we end up hearing. Amplitude modulation

3:09radio communication has a number of useful features. It's exceptionally simple and can work over huge distances, but it does tend to be highly susceptible to outside interference. That's a big reason why AM radio tends to be lower quality, and a big reason why it's not as useful a technique for transmitting bigger chunks of data. Of course, the wavelength can also be manipulated. That means that we can essentially do the same thing, but this time by ever so slightly modifying the distance between waves. In this context, we'd refer to this as the frequency, which is proportional to wavelength, but rather than being a physical measure, it's a temporal one. How many times the wave oscillates within a second? So, by slightly modulating frequency, we can transmit the same audio signal, but since this method is less susceptible to interference, we can generally get higher quality. Now, traditional radio works by encoding the audio signal itself into radio waves using amplitude or frequency modulation, but computers, phones, essentially everything digital nowadays encodes

4:10its data into binary code, sequences of ones and zeros. This only makes communication using electromagnetic radiation better. We could set it up so that when the amplitude is high that corresponds to a one, while when it's low, it corresponds to a zero, or rather, when frequency is high, that's a one, and when low, that's a zero. This is simple and already more efficient than encoding the analog audio signal, but it could be even more efficient. That's because there's yet another wave property that we can manipulate. For these purposes, we can consider one full cycle of a wave going up, down, and up again, one phase. But we can also consider this, the wave going down, then up, then down again, one phase as well. Therefore, we could assign this upward phase to the binary digit one, and this one, the downward phase to the binary digit zero. Then, we can transmit data using a sequence of these different phases. The transmitter doesn't need one phase to

5:10seamlessly go into the next, so it's an even faster, even more efficient way of encoding binary sequences into electromagnetic radiation. But here's where things get really cool. There can be more than two phases. We could divide the cycle into one phase starting at the midpoint going upward, one starting at the crest, one starting at the midpoint going downward, and one starting at the trough. So with four distinct phases, one can correspond to the binary sequence zero one, one to one one, one to one zero, and one to zero zero zero. Therefore, we can cram twice as much data into the same signal. But it doesn't stop there. We can even take this a step further and have eight distinct phases so that we can transmit every possible three digit sequence of ones and zeros, thereby tripling efficiency. Eight distinct phases is typically the practical limit for wireless data transmission. It becomes too tough to distinguish between phases with any more, so the error rate is too high. However, this is just manipulating one property of the wave,

6:13and there are, of course, two others. This phase, initially upward from the midpoint, could be broadcast at a high amplitude or a low amplitude. So we can say that the low amplitude version of this correlates to the binary sequence zero zero zero zero, while the high amplitude version zero zero zero one. By adding two amplitude options to each of the eight phases, we get 16 total transmission options, meaning we have enough to correlate to each of the 16 possible four digit combinations of zeros and ones. If we haven't accurate enough method of transmission, we could further increase the number of phase and amplitude combinations to a total of 64, each corresponding to a six digit binary sequence. In fact, the newest Wi-Fi standards have 1,024 phase and amplitude combinations, while extremely accurate copper twisted cables can deal with 32,768 combinations, each corresponding to a 15 digit sequence. Constrained by the accuracy of wireless communication, your cell phone,

7:15meanwhile, uses as few as 16 combinations in the case of some 3G networks and as many as 1,024 in the most advanced 5G networks. Fundamentally though, this is how your cell phone gets a lot of data out of a little slice of the radio spectrum. Of course, transmitting data is only half the battle. Something also needs to receive it. That something is, of course, a cell site. Now, keep in mind that a cell phone is essentially just a fancy walkie-talkie. It uses the exact same process just more advanced. In fact, the earliest portable phones, carphones were just one step removed from walkie-talkies. A telephone company would set up a radio transmitter in a city, users would install a bulky system in their car, the system would communicate with the transmitter just as a walkie-talkie would, and the tower would then plug the signal into the landline network. Put another way, it was just a citywide version of cordless landlines. The only difference from walkie-talkies was that these carphones would have a dedicated channel for outbound transmission

8:16and a dedicated channel for inbound transmission so that both sides could talk simultaneously, unlike with a walkie-talkie where one needs to wait and push to talk since only one channel is used. These carphones were fairly similar to today's cell phones from a user experience perspective, but they were horribly inefficient. In their early days, there were only 32 available channels, meaning only 32 people in a city could use their carphones simultaneously. In addition, if one left the service area of that one tower in their home city, their carphones wouldn't work. Of course, the solution was cells. The idea was this, a given area would be split up into a pattern of hexagons. At the center of each of those hexagons was a cell site. These are generally thought of as cell towers, but that's a misnomer since cell sites can be located on buildings, inside church seapoles at the tops of mountains, or really anywhere that's elevated relative to the typical user. Fundamentally, these cell sites just send and receive radio signals to and from cell phones, which is a fairly simple process. Then, they need a way to plug into the wired

9:19communication network to convey data over longer distances. Often, this is accomplished through physical fiber optic cables, but especially in more rural areas, that's not always practical. If one put a cell site on the top of a mountain, for example, it would likely have to operate completely off-grid, powered by solar or a generator, and it also couldn't physically plug into the wired communication network due to its isolation. Therefore, these more remote cell sites use microwave transmitters. Now, tiny microwaves, thanks to their extremely rapid frequency, are incredibly efficient at moving huge amounts of data fast. The most advanced systems have reached over 100 gigabits per second, but they're not very resilient. One needs a direct line of site between the transmitter and receiver to accurately transmit, which prevents microwaves use for portable cell phones. However, for fixed cell sites, this is possible. So, many are set up with microwave transmission systems that relay signal to the closest site with a physical link to the wired communication network. With both a wired and wireless option, cell sites can be located

10:23anywhere, which is important because their location absolutely matters. Centering their hexagon, the signal from each of these sites must reach far enough that there is some overlap between the cells. That way, if a cell phone is being used on the move, the call can be seamlessly passed from one cell site to the next with no drop-off in signal, and the network can be expanded far beyond the reach of one transmitter. However, the system starts to seem less ingenious once you do the math. Originally, only 832 different frequencies were allocated for use by cell phones. There are a lot of different uses for the radio spectrum, so regulatory bodies like the American FCC, British Off-Com, or German B-Nezza can only allocate so many frequencies for different industries, and spectrum allocation is crucial so that two users don't try to use the same frequency, which would render both of their uses useless. So, of those 832 frequencies, 42 were used by the cell network for its own back-end internal communication. That left 790, but a call-repired both an outbound and inbound

11:26frequency effectively meaning there were only 395 call channels. However, in order to prevent interference, no two bordering cells could use the same frequency. As each hexagon had six neighbors, that meant each cell could only use one-seventh of the available channels. So, each cell had 56 channels, meaning 56 users within each cell could make a call at a given. This initially worked fine, but then cell phones got popular. To keep up with the manned, cell carriers needed to find a way to do more with a single frequency. When the second generation of mobile networks came along, calls were no longer transmitted as analog audio waves. Rather, they started to use those digital signals encoded using phase and amplitude. The thing was, this method was more efficient, meaning using a whole channel to transmit a single voice conversation was overkill, one only needed part of it. Of course, the difficulty was that voice conversations happen in real time. It's not like you could compress an entire two-minute call and send it at the

12:30end. Therefore, cell companies divided a given channel into eight time slots. These time slots would rotate one after another in rapid succession, and a given phone would be told to use, say, the third time slot. So, each time that time slot came up, it would fire off its ones and zeros quickly, then wait for it to come around again. But because the data was compressed into an efficient digital signal, the amount received during a time slot would be enough to decode into enough of the conversation to play until the next time slot came up. This system meant that one channel could now be used by eight phones simultaneously. What was 56 channels now became 448. But eventually, as phones became ever more commonplace, the system of time division multiple access became, once again, not good enough. The next evolution was where things got complicated, but also fascinating. It's called Code Division Multiple Access. It's an ingenious way where multiple

13:32phones can send and receive data on the same channel truly simultaneously. To explain the incredibly simple version, let's say a first user wants to transmit the binary sequence 11, a second user 01, and a third one zero. Now, each of these users would be allocated what's called a spreading code, 0101, 01011, and 0000 respectively. For the first user, their first binary digit, one, would be compared to each of the four digits of their spreading code. If the spread code digit and the binary digit is the same, it will output a zero. If it's different, it will output a one. So, for user one, the output sequence would be 10101010. The process would repeat for user 2, which output 00111, 1100, and user 3, which outputs 1111000. Next, the sequences are translated so that zeros become positive ones and ones become negative ones. Then, each digit of the three sequences

14:35of numbers are added together. That outputs the composite sequence, negative 11, negative 3, negative 1, negative 1113. This composite sequence is what is then transmitted using a single channel. Now, the exact details of this process are not tremendously important, but what is is what happens next. What happens next is that this process is reversed. So, the receiver of that composite sequence would know each user's unique spreading code. The spreading code is also translated so that zeros become positive ones and ones become negative ones. And then, the receiver multiplies the composite sequence with this translated spreading code. For user one, that outputs negative 1, negative 1, negative 3, one, negative 1, negative 1, one, negative 3. Now, the first four digits of this sequence, which we know correlate with the first digit of the data, are added together to get negative 4, which is then divided by 4 to get negative 1. The process repeats for the second set of 4 to get negative 1. Now, if we translate this back so that negative ones become ones and positive

15:37ones become zeros, then we get the data sequence, 1, 1. With just the composite sequence and the unique spreading code, this process figured out what user one's unique data sequence was. If we repeat this entire decoding process with user 2 spreading code, we get 0, 1. It's data sequence, and unsurprisingly, it also works for user 3. So, with one composite signal and three unique spreading codes, we are able to triple up the use of one channel. In practice, this process works at a much larger, much more complex scale, but it uses these same mathematical principles. This, fundamentally, is how cell service works. Making a 2 way radio work for one person is simple. Making a 2 way radio work for everyone in the same area at the same time is difficult. It's all about packing as much data as possible into a single transmission, and then packing as many transmissions as possible into a single radio wave. The aforementioned techniques to accomplish

16:40these two goals are only the tip of the iceberg. Many of the most advanced networks have moved on to a system called orthogonal frequency division multiple access to pack even more transmissions into a single wavelength, for example, but they are indicative of the process that got us to today. When we move from 3G to 4G and 4G to 5, what's happening in the background is incredibly smart people finding more and more ingenious methods of transmitting more data using the same resources, also that we, the end users, can browse Twitter and watch YouTube just ever so slightly faster. Now that this video is over, I am extremely excited to announce that in just two weeks, we'll be releasing our first ever feature length documentary. It's called the Colorado problem, a river in the red. Never before have I been more surprised that this story isn't covered more. The Colorado river, the river that single-handedly supplies water for the entire desert region of the American southwest, is becoming smaller and smaller and smaller each year and the reserves are almost gone.

17:43Put another way, in much of Utah, Nevada, Arizona, and California, people need more water than they can get. Our documentary covers what led to such a cataclysmic problem and the harsh reality of the future for the American Southwest. You'll be able to watch it on either CuriosityStream or Nebula when it releases on February 8th, but of course, if you're not currently a subscriber of either of those streaming services, the CuriosityStream Nebula bundle deal, available on sale now for less than $15 a year at curiositystream.com slash whendover, gets you access to both. CuriosityStream has a huge catalogue of top-quality non-fiction shows and documentaries while Nebula is the streaming site founded by creators, including myself, to act as the best home to the stuff we make. It features all our normal videos early and ad-free, occasional exclusive behind-the-scenes and companion videos, as well as the big budget Nebula originals that many of you know so well. So, make sure to block off 90 minutes on February 8th to watch the Colorado problem, and if you haven't already, head to curiositystream.com slash whendover or click the button on screen to get

18:44both Nebula and the CuriosityStream for less than what you pay for a month of the largest streaming services, and you'll be helping support Wendover and tons of other independent creators while you're at it.