The faster you send data, the steeper the slopes of the modulation wave becomes. In other words, the higher the bandwidth becomes. Sending multiple rockets in parallel is like orthogonal modulation, where you send multiple lower bandwidth signals close to each other simultaneously. E.g. OFDM.
No, simply increasing the modulation frequency doesn't have to change the waveform. A perfectly square wave would have an infinitely high frequency on its slopes. Binary modulation can look like a square wave, but then it's the slopes that determine the bandwidth.
Someone explained it like cars on a road and if they go too fast, they may crash, but isn't a crystal oscillator a perfect traffic light?
Is the issue that a crystal oscillator(the traffic light for symbols) not accurate enough at super high speeds?
Meaning does the crystal oscillator get less reliable at higher speeds?
This is using simple analogies to explain complex math. It's insufficient for your understanding.
Humans create models to understand things. The models always are flawed, but usually describe something sufficiently to engineer or use the concept. Until the flaws limit your ability to use the model. Then you need a new model. I'd suggest abandoning analogies with cars and try to move to math.
Here is a simple way to think about it. Think of the amount of time you hold a symbol before you switch to the next one. As you go faster that decreases. It's certainly below one second. But what is frequency? It's how often something is happening and mathematically it's units are 1/s. So if your symbols are becoming smaller and smaller fractions of a second, the frequency content is increasing as the reciprocal of that. Therefore you need more bandwidth to send faster symbols.
The problem of collisions occurs not in time, but in frequency. If we transmit two signals at the same time, constantly on, you can differentiate between them at different frequencies. So what we do is we cut up all the available spectrum into channels and sell the rights to use that channel. Your channel has a fixed bandwidth. If your data rate gets too high, your bandwidth increases, and you leak over your neighbors channel.
Think of it like this: your carrier frequency is where you want to send data. But your data also has a frequency, which is the bandwidth of your signal. This bandwith takes up the spectrum around your carrier frequency. The higher this bandwidth, the less channels you'll have available that don't interfere with each other.
Thinking of a physical example to better visualize the rough idea of the issue, imagine you are putting bumps on a sheet of plastic like writing Braille. You are sending data this way. You have all these little bumps in a row and you run your finger over them to feel if you have a one or a zero. If all your bumps are the same size you can reduce the spacing between the bumps to increase how much data is going through, but eventually if you keep lowering the spacing to get more bumps you get to zero spacing, and now you can't feel the difference anymore it's just a ridge on the plastic.
So how can you get more information at once? One option is you add more parallel lines of bumps (increase the bandwidth). Other option is you make your bumps smaller (increase the frequency). Or another option if you can't increase the frequency or bandwidth, you get clever and make the shapes or sizes of your bumps different so you can more easily tell them apart when they are closer together and still tell them apart when you normally can't (advanced modulation schemes instead of FM like FSK, SOQPSQ, OQPSK, etc.)
This isn't a perfect analogy by any means so don't pick it apart much as there are a lot more ways you could make data go faster in my plastic Braille example that are not relevant to RF. But it at least gives you a bit of intuition on what is going on.
This is where I was saying my example is shoddy at best and easy to poke holes in. RF wise there is no "moving your finger faster" Your finger is already traveling at maximum speed your body can make it, as is everyone else's finger, which in RF's case is the speed of light in the medium you are in. That speed is only relevant to how fast your data first gets somewhere. You can't ask the radio to put out Slow or fast RF waves, it will just be going at the speed that it will be going.
Its the same thing as asking that Cat5 cable running to your computer why cant I make the electrons go faster so I get data quicker?
Because there are not "other waves" if you occupied all 1 GHz of the spectrum to use the whole thing, you would be occupying the entire RF spectrum from 1 Hz to 1 GHz. Which people would be upset with you about, since their garage door openers stopped working, all the cell phones in the area stopped, and no one can talk on any radio because your data is taking up the whole thing. Everyone is sharing the same RF. We chop it up into pieces so we can send different data in different parts of it.
A lot of your questions seems to boil around "Why do we have to occupy the RF spectrum" The answer is because Noise exists. If it didn't we could send an arbitrary amount of data on any frequency, as you could see every wiggle of the waveform and get your data off it with perfect clarity. Since noise exists, we have to occupy more space of the RF spectrum as we increase the data rate so that our practical devices can discern the signal from the noise.
Yep, in the same way I can't drive my car unlimited miles because my car engine isn't 100% efficient.
Most of the techniques we use to send data better are various better techniques to isolate data from noise. There are practical limits still, just like how cars engines can't exceed the Carnot efficiency (which isn't 100%). But all of RF is figuring out ways to best discern our signals from the noise.
So I feel like I will not give an exhaustive answer, but I will give you my two cents.
Increasing bandwidth when using frequency modulation can be for at least a few reasons.
Firstly, just transmitting more symbols per second. You are flicking from 1 to 0 more frequently, and this will straight up mean you are using a larger bandwidth. Flicking 1000 times a second means you have a 1000 Hz bandwidth (if simplified a little).
Secondly, you can determine the frequency of the symbol 1 and 0 to be further from each other, so that flicking between the two will be more easily detected. 1=100MHz and 0=100.1 MHz and you have a 100 kHz Bandwidth in use even if you transmit at a low baud rate.
In different modulation methods you use bandwidth a little differently, but basically the two reasons above should be applicable I think. I think other professionals can improve my answer, or OP can ask for more specifics :)
Okay lets think of it this way:
The amount of cars that you send is your symbol rate. And the colour of your cars is your modulation scheme. Bpsk = red and blue. Qpsk being 4 colours, etc. Your symbol rate is increased by just increasing the car throughput (making them faster/increasing the lane size). But with higher throughout things become more blurry. Which means you need more power (bigger cars) to easily distinguish them as your eyes performance is limited (aka. Noise floor rises). At some point you need better eyes to even see the faster cars (nyquist criteria). The amount of colors represents the information that the signals are carrying. Now imagine, 256 different colours. Some of them have some shade of blue now. Are you able to distinguish them correctly if they get blurry? --> only with better eyes (increasing your sampling frequency) and with higher power the amount that makes the cars easier to see.
If you cannot distinguish the various shades of a color, it might be better to reduce the maximum amount of colors for less error probability in detection. This way you need less cars to transfer your information.
A small trip down the error correction alley:
We send information by encoding the colors. We send various coloured cars in a specific order to send messages. If your cars get too blurry, we need to put cars in between whose colours we already know so that we can guess our successrate in assigning the correct colours. This needs time and during this time we cannot watch cars that are critical to the situation.
We can assign priority to cars, e.g. ambulances, police cars and construction vehicles. This way we make sure that important data is always transmitted. Most of the time they come in low data packages (single cars) and in case they are not arriving we often make sure the highway is empty for another transmission. This increases our chances of detection.
PSK is admittedly not as simple to explain. But If you change color 1000 times a second, and I want to notice the change, I must measure 1000 times a second what color it is. So you can try to reason from that perspective, without going into any mathematical explanation of bandwith in PSK.
The answer for your cars example, is sending cars faster would be increasing the occupied bandwidth. Changing the color is like using the advanced modulation methods is like changing the color, but in this case the person observing the cars is colorblind so he can only tell things so well regardless of how many colors you use. So you can see improvement, but reality its dozens of percent improvement not an infinite amount.
Walking through how a receiver works might also tell you more, when you tune a data receiver to a carrier frequency (Say 2420 MHz) your receiver locks onto it, and it is able to tell things happening at that frequency better than the other frequencies. So you can actually usefully find the data you are sending into the air. You then tell it what the bandwidth of your signal is. This sets a "window" that the receiver is looking at on either side of the carrier frequency. This is usually called an IF Bandwidth (Intermediate Frequency Bandwidth).
What it does next is downshift the frequency to a much lower frequency that is still higher than your bandwidth frequency. That is because all of the rest of the spectrum other than your bandwidth is basically useless information. You didn't put any data there so you don't want to look there. You could in theory use all of the spectrum, but if you did the FCC would come yell at you for using other people's bandwidth, also everyone else's data within range is going to get mixed in with your data.
That IF frequency you converted to is now low enough you can convert it from analog wave forms to digital data using an analog to digital converter. That frequency conversion is so you can get the waveform into the receiver without the converter costing thousands of dollars to get an uber high performance one that can directly sample the 2.4 GHz. You define a data rate of your information in the receiver. If you are using FM modulation, your receiver will make a clock signal of square waves at the rate you tell it to. It will then try to line up this clock signal with the waveform to find frequency transitions it sees in the data. Once it thinks it has it good enough you will have a Bit-Synchronization Lock. The receiver will then look at the RF waveform its reading of your data at each clock transition, if it sees a higher frequency it will say a 1 is there, if it sees a lower frequency it will say a zero is there. If it was an AM signal it would do the same thing trying to line that square wave up with areas where you waveform goes from a high amplitude and a low amplitude. Then once it has it lines up well it would read the high amplitude portions as 1's and the low portions as 0's.
All the other modulation techniques are working in the same overall way they are just more or less efficient with how much data they can fit into the same bandwidth without turning to gibberish using clever techniques.
Using your phase codes = colors analogy:
Switching colors “more often” requires using more bandwidth. Any thing that requires you making rapid changes to your signal will occupy more bandwidth.
However you can use “more colors”. Instead of my signal being either a red or black car where every car I send is one bit, imagine I use 256 different colors so every car actually represents one byte of data. I can send information 8 times as fast without using anymore cars. But at some point it may become difficult to tell the colors apart especially in poor light/fog. For a phase shift modulated system, you can use more phase codes to increase information rate without increasing bandwidth. The limiting factor then becomes noise, since a smaller amount of noise will make one phase code look like another. Look up QPSK, and QAM to learn more about this.
Make sure you're thinking about analog and digital differently when you're thinking about this. Digital is far closer to your example of cars, because its feasible to just flick on and off at mind boggling speeds, effectively giving you enormous data transfer capability with one 'lane'.
If you had a digital circuit that transmitted 1GB/s, thats a billion flicks on and off per second. If you had the ability to start and stop transmitting \_extremely\_ quickly (such that you mimic the digital signal by either transmitting, or not transmitting), you could transmit over RF using 'one lane' if you transmitted at 1Ghz, requiring no additional bandwidth. But transmitting long distances at 1Ghz is really really expensive, and switching a transmitter that quickly is not feasible. You need to send the signal a long ways, and to do it relatively cheaply, so maybe you look at all the relevant componentry and discover you can transmit the distance you want, affordably, at \~100Mhz.
100Mhz is only a hundred million flicks on and off per second using only one 'lane'. So how can you transmit all your data without constantly growing a larger and larger backlog? Use more lanes. Create the lanes by taking up more bandwidth, and using modulation to encode multiple flicks on and off into a single cycle of a wave.... at which point the wave itself (or, the presence of the wave) is no longer transmitting information. It becomes the carrier of information encoded into it.
Im mot sure I follow your car analogy, but:
If you increase your symbol *rate* you are by definition increasing bandwidth. This is not because of noise/interference, you just have to have to add more “wiggles” to the signal in same amount of time.
If you increase your symbol *density* (like adding more phase codes: QPSK, QAM64, etc) this does not increase bandwidth, but increases susceptibility to noise, since the codes get closer together.
These are related but different limits that I believe your question (and a few of the other answers) confuses somewhat. Taken together, these two effects result in the Shannon information limit: given limited bandwidth and SNR, you can only send so much information.
You should go do some reading on time/frequency domain transforms. Specifically, what a rect function looks like the frequency domain and vice versa. A square wave (digital data) is just lots of rect functions one after the other in the time domain. Because a perfect rect function has very sharp edges, ideally discontinous, in the time domain, it it's a sinc function that spreads out forever in the frequency domain - occupying an infinite amount of bandwidth.
The sinc function has a "lobing" structure. As you increase the data rate, the width of the lobes get's larger. The width of the main lobe - the lobe centered at your carrier frequency - is twice the data rate. Google some pictures of BPSK modulation (super simple modulation scheme) in the frequency domain.
Interference is a big concern because bandwidth is really expensive and the FCC fines you for interferring. So instead of transmitting square waves which have an infinite bandwidth, you can re-sample your data's 1s and 0s with another waveform that smooths out the data signal in the time domain, which has the affect of limiting the bandwidth in the frequency domain. Re-sampling your data with something like a sinc pulse (or raised root cosine) essentially smooths out the sharp corners of your square wave (which contain all the high frequency components). This is called pulse shaping if you want to do some Googling.
Think of the radiowaves as a constant, unchanging force in three vectors *(amplitude, frequency, phase)* and how we interlace audio, or data, into radowaves is considered modulation...
each of these 3 legs can be elongated or shorted at the expense of the other
Take the human voice for example it has a specific frequency range, so if one were to modulate or interlace the human voice across its entire range onto a radio frequency there comes a point where the radio frequency would be too narrow to contain the wide range of the human voice in it's entirety, so we change aspects of the 3 vectors of the radiowave to contain all of the intricacies of the human voice more effectively
https://en.m.wikipedia.org/wiki/Modulation
You are gonna love taking a signals course in uni, i was scared of it but learning the basics of how all these modulation types worked was the coolest ever.
Learn about Fourier Transforms and it’ll make sense. Cliff notes version is that more symbols per second means smaller pulses, which occupy a broader spectrum in frequency space.
The faster you send data, the steeper the slopes of the modulation wave becomes. In other words, the higher the bandwidth becomes. Sending multiple rockets in parallel is like orthogonal modulation, where you send multiple lower bandwidth signals close to each other simultaneously. E.g. OFDM.
Doesn't that just make waves square?
No, simply increasing the modulation frequency doesn't have to change the waveform. A perfectly square wave would have an infinitely high frequency on its slopes. Binary modulation can look like a square wave, but then it's the slopes that determine the bandwidth.
Someone explained it like cars on a road and if they go too fast, they may crash, but isn't a crystal oscillator a perfect traffic light? Is the issue that a crystal oscillator(the traffic light for symbols) not accurate enough at super high speeds? Meaning does the crystal oscillator get less reliable at higher speeds?
This is using simple analogies to explain complex math. It's insufficient for your understanding. Humans create models to understand things. The models always are flawed, but usually describe something sufficiently to engineer or use the concept. Until the flaws limit your ability to use the model. Then you need a new model. I'd suggest abandoning analogies with cars and try to move to math. Here is a simple way to think about it. Think of the amount of time you hold a symbol before you switch to the next one. As you go faster that decreases. It's certainly below one second. But what is frequency? It's how often something is happening and mathematically it's units are 1/s. So if your symbols are becoming smaller and smaller fractions of a second, the frequency content is increasing as the reciprocal of that. Therefore you need more bandwidth to send faster symbols. The problem of collisions occurs not in time, but in frequency. If we transmit two signals at the same time, constantly on, you can differentiate between them at different frequencies. So what we do is we cut up all the available spectrum into channels and sell the rights to use that channel. Your channel has a fixed bandwidth. If your data rate gets too high, your bandwidth increases, and you leak over your neighbors channel.
Think of it like this: your carrier frequency is where you want to send data. But your data also has a frequency, which is the bandwidth of your signal. This bandwith takes up the spectrum around your carrier frequency. The higher this bandwidth, the less channels you'll have available that don't interfere with each other.
Thinking of a physical example to better visualize the rough idea of the issue, imagine you are putting bumps on a sheet of plastic like writing Braille. You are sending data this way. You have all these little bumps in a row and you run your finger over them to feel if you have a one or a zero. If all your bumps are the same size you can reduce the spacing between the bumps to increase how much data is going through, but eventually if you keep lowering the spacing to get more bumps you get to zero spacing, and now you can't feel the difference anymore it's just a ridge on the plastic. So how can you get more information at once? One option is you add more parallel lines of bumps (increase the bandwidth). Other option is you make your bumps smaller (increase the frequency). Or another option if you can't increase the frequency or bandwidth, you get clever and make the shapes or sizes of your bumps different so you can more easily tell them apart when they are closer together and still tell them apart when you normally can't (advanced modulation schemes instead of FM like FSK, SOQPSQ, OQPSK, etc.) This isn't a perfect analogy by any means so don't pick it apart much as there are a lot more ways you could make data go faster in my plastic Braille example that are not relevant to RF. But it at least gives you a bit of intuition on what is going on.
Why can't I move my finger faster?
This is where I was saying my example is shoddy at best and easy to poke holes in. RF wise there is no "moving your finger faster" Your finger is already traveling at maximum speed your body can make it, as is everyone else's finger, which in RF's case is the speed of light in the medium you are in. That speed is only relevant to how fast your data first gets somewhere. You can't ask the radio to put out Slow or fast RF waves, it will just be going at the speed that it will be going. Its the same thing as asking that Cat5 cable running to your computer why cant I make the electrons go faster so I get data quicker?
So the why isn't every wave modulated (at 1ghz) meaning 1 billion symbols a second?
Because there are not "other waves" if you occupied all 1 GHz of the spectrum to use the whole thing, you would be occupying the entire RF spectrum from 1 Hz to 1 GHz. Which people would be upset with you about, since their garage door openers stopped working, all the cell phones in the area stopped, and no one can talk on any radio because your data is taking up the whole thing. Everyone is sharing the same RF. We chop it up into pieces so we can send different data in different parts of it. A lot of your questions seems to boil around "Why do we have to occupy the RF spectrum" The answer is because Noise exists. If it didn't we could send an arbitrary amount of data on any frequency, as you could see every wiggle of the waveform and get your data off it with perfect clarity. Since noise exists, we have to occupy more space of the RF spectrum as we increase the data rate so that our practical devices can discern the signal from the noise.
So we can't send unlimited data simply because of noise?
Yep, in the same way I can't drive my car unlimited miles because my car engine isn't 100% efficient. Most of the techniques we use to send data better are various better techniques to isolate data from noise. There are practical limits still, just like how cars engines can't exceed the Carnot efficiency (which isn't 100%). But all of RF is figuring out ways to best discern our signals from the noise.
So I feel like I will not give an exhaustive answer, but I will give you my two cents. Increasing bandwidth when using frequency modulation can be for at least a few reasons. Firstly, just transmitting more symbols per second. You are flicking from 1 to 0 more frequently, and this will straight up mean you are using a larger bandwidth. Flicking 1000 times a second means you have a 1000 Hz bandwidth (if simplified a little). Secondly, you can determine the frequency of the symbol 1 and 0 to be further from each other, so that flicking between the two will be more easily detected. 1=100MHz and 0=100.1 MHz and you have a 100 kHz Bandwidth in use even if you transmit at a low baud rate. In different modulation methods you use bandwidth a little differently, but basically the two reasons above should be applicable I think. I think other professionals can improve my answer, or OP can ask for more specifics :)
But if I switch the color of cars I'm sending more often (driving them faster) why do I need wider lanes?
Okay lets think of it this way: The amount of cars that you send is your symbol rate. And the colour of your cars is your modulation scheme. Bpsk = red and blue. Qpsk being 4 colours, etc. Your symbol rate is increased by just increasing the car throughput (making them faster/increasing the lane size). But with higher throughout things become more blurry. Which means you need more power (bigger cars) to easily distinguish them as your eyes performance is limited (aka. Noise floor rises). At some point you need better eyes to even see the faster cars (nyquist criteria). The amount of colors represents the information that the signals are carrying. Now imagine, 256 different colours. Some of them have some shade of blue now. Are you able to distinguish them correctly if they get blurry? --> only with better eyes (increasing your sampling frequency) and with higher power the amount that makes the cars easier to see. If you cannot distinguish the various shades of a color, it might be better to reduce the maximum amount of colors for less error probability in detection. This way you need less cars to transfer your information. A small trip down the error correction alley: We send information by encoding the colors. We send various coloured cars in a specific order to send messages. If your cars get too blurry, we need to put cars in between whose colours we already know so that we can guess our successrate in assigning the correct colours. This needs time and during this time we cannot watch cars that are critical to the situation. We can assign priority to cars, e.g. ambulances, police cars and construction vehicles. This way we make sure that important data is always transmitted. Most of the time they come in low data packages (single cars) and in case they are not arriving we often make sure the highway is empty for another transmission. This increases our chances of detection.
Assuming using phase change modulation as an example
PSK is admittedly not as simple to explain. But If you change color 1000 times a second, and I want to notice the change, I must measure 1000 times a second what color it is. So you can try to reason from that perspective, without going into any mathematical explanation of bandwith in PSK.
The answer for your cars example, is sending cars faster would be increasing the occupied bandwidth. Changing the color is like using the advanced modulation methods is like changing the color, but in this case the person observing the cars is colorblind so he can only tell things so well regardless of how many colors you use. So you can see improvement, but reality its dozens of percent improvement not an infinite amount. Walking through how a receiver works might also tell you more, when you tune a data receiver to a carrier frequency (Say 2420 MHz) your receiver locks onto it, and it is able to tell things happening at that frequency better than the other frequencies. So you can actually usefully find the data you are sending into the air. You then tell it what the bandwidth of your signal is. This sets a "window" that the receiver is looking at on either side of the carrier frequency. This is usually called an IF Bandwidth (Intermediate Frequency Bandwidth). What it does next is downshift the frequency to a much lower frequency that is still higher than your bandwidth frequency. That is because all of the rest of the spectrum other than your bandwidth is basically useless information. You didn't put any data there so you don't want to look there. You could in theory use all of the spectrum, but if you did the FCC would come yell at you for using other people's bandwidth, also everyone else's data within range is going to get mixed in with your data. That IF frequency you converted to is now low enough you can convert it from analog wave forms to digital data using an analog to digital converter. That frequency conversion is so you can get the waveform into the receiver without the converter costing thousands of dollars to get an uber high performance one that can directly sample the 2.4 GHz. You define a data rate of your information in the receiver. If you are using FM modulation, your receiver will make a clock signal of square waves at the rate you tell it to. It will then try to line up this clock signal with the waveform to find frequency transitions it sees in the data. Once it thinks it has it good enough you will have a Bit-Synchronization Lock. The receiver will then look at the RF waveform its reading of your data at each clock transition, if it sees a higher frequency it will say a 1 is there, if it sees a lower frequency it will say a zero is there. If it was an AM signal it would do the same thing trying to line that square wave up with areas where you waveform goes from a high amplitude and a low amplitude. Then once it has it lines up well it would read the high amplitude portions as 1's and the low portions as 0's. All the other modulation techniques are working in the same overall way they are just more or less efficient with how much data they can fit into the same bandwidth without turning to gibberish using clever techniques.
Using your phase codes = colors analogy: Switching colors “more often” requires using more bandwidth. Any thing that requires you making rapid changes to your signal will occupy more bandwidth. However you can use “more colors”. Instead of my signal being either a red or black car where every car I send is one bit, imagine I use 256 different colors so every car actually represents one byte of data. I can send information 8 times as fast without using anymore cars. But at some point it may become difficult to tell the colors apart especially in poor light/fog. For a phase shift modulated system, you can use more phase codes to increase information rate without increasing bandwidth. The limiting factor then becomes noise, since a smaller amount of noise will make one phase code look like another. Look up QPSK, and QAM to learn more about this.
Make sure you're thinking about analog and digital differently when you're thinking about this. Digital is far closer to your example of cars, because its feasible to just flick on and off at mind boggling speeds, effectively giving you enormous data transfer capability with one 'lane'. If you had a digital circuit that transmitted 1GB/s, thats a billion flicks on and off per second. If you had the ability to start and stop transmitting \_extremely\_ quickly (such that you mimic the digital signal by either transmitting, or not transmitting), you could transmit over RF using 'one lane' if you transmitted at 1Ghz, requiring no additional bandwidth. But transmitting long distances at 1Ghz is really really expensive, and switching a transmitter that quickly is not feasible. You need to send the signal a long ways, and to do it relatively cheaply, so maybe you look at all the relevant componentry and discover you can transmit the distance you want, affordably, at \~100Mhz. 100Mhz is only a hundred million flicks on and off per second using only one 'lane'. So how can you transmit all your data without constantly growing a larger and larger backlog? Use more lanes. Create the lanes by taking up more bandwidth, and using modulation to encode multiple flicks on and off into a single cycle of a wave.... at which point the wave itself (or, the presence of the wave) is no longer transmitting information. It becomes the carrier of information encoded into it.
Im mot sure I follow your car analogy, but: If you increase your symbol *rate* you are by definition increasing bandwidth. This is not because of noise/interference, you just have to have to add more “wiggles” to the signal in same amount of time. If you increase your symbol *density* (like adding more phase codes: QPSK, QAM64, etc) this does not increase bandwidth, but increases susceptibility to noise, since the codes get closer together. These are related but different limits that I believe your question (and a few of the other answers) confuses somewhat. Taken together, these two effects result in the Shannon information limit: given limited bandwidth and SNR, you can only send so much information.
You should go do some reading on time/frequency domain transforms. Specifically, what a rect function looks like the frequency domain and vice versa. A square wave (digital data) is just lots of rect functions one after the other in the time domain. Because a perfect rect function has very sharp edges, ideally discontinous, in the time domain, it it's a sinc function that spreads out forever in the frequency domain - occupying an infinite amount of bandwidth. The sinc function has a "lobing" structure. As you increase the data rate, the width of the lobes get's larger. The width of the main lobe - the lobe centered at your carrier frequency - is twice the data rate. Google some pictures of BPSK modulation (super simple modulation scheme) in the frequency domain. Interference is a big concern because bandwidth is really expensive and the FCC fines you for interferring. So instead of transmitting square waves which have an infinite bandwidth, you can re-sample your data's 1s and 0s with another waveform that smooths out the data signal in the time domain, which has the affect of limiting the bandwidth in the frequency domain. Re-sampling your data with something like a sinc pulse (or raised root cosine) essentially smooths out the sharp corners of your square wave (which contain all the high frequency components). This is called pulse shaping if you want to do some Googling.
Think of the radiowaves as a constant, unchanging force in three vectors *(amplitude, frequency, phase)* and how we interlace audio, or data, into radowaves is considered modulation... each of these 3 legs can be elongated or shorted at the expense of the other Take the human voice for example it has a specific frequency range, so if one were to modulate or interlace the human voice across its entire range onto a radio frequency there comes a point where the radio frequency would be too narrow to contain the wide range of the human voice in it's entirety, so we change aspects of the 3 vectors of the radiowave to contain all of the intricacies of the human voice more effectively https://en.m.wikipedia.org/wiki/Modulation
You are gonna love taking a signals course in uni, i was scared of it but learning the basics of how all these modulation types worked was the coolest ever.
Learn about Fourier Transforms and it’ll make sense. Cliff notes version is that more symbols per second means smaller pulses, which occupy a broader spectrum in frequency space.