Ok , I pretty much know all the major ways of modulating digital and analog data. In principle there are only 3 ways to vary a sine/cosine carrier wave
amp , phase , frequency ( digital are ASK , PSK ,FSK / analog versions are AM ,PM ,FM )
Most of the ones used are a combination of them like QAM 16,64,256 ,...etc as well as others.
I also know to have multiple people using a wireless or wired media at the same time you either have to do some sort of round robin or multiplexing technique.
For the round robin you could use CSMA avoidance/detection techniques or just a time slot.
If you want to transmit all people at the same time then you would have to do some multiplex technique like TDM ,FDM CDMA ,COCDMA , ...etc etc there are many choices but in principle they all use some form of time, amplitude , frequency , phase , use multiple carriers (i.e vary shape) and or combination of them to allow people to transmit all at the same time with no interference. (I know by doing the math which ones are better in which situations )
Channel based transmissions ones that are used in mobile phone networks MUST USE MULTPLEXING or then we would have chaos if a ton of people wanted to use it forget round robin or waiting.
But then we have Packet based based transmissions like the ones in 802.11 or ethernet home LANS. In these multiple people really cann't transmit all at once like the mobile phone network allows but they use CSMA detection/avoidance which usually a person wireless/wired card waits for the channel to be clear to send. Same thing when it comes to going out my cable internet modem.
I am curious why don't we just all use the multiplex techniques and stop using the CSMA stuff and use the multiplexing technique that allow us to have many people sending there data all at once. (i,e with no waiting to see if the channel is clear or other things)
Question 2
Is this sort of CSMA avoidance/detection / time slot info sending just used in the computer LAN and modems to the ISP. Or is there more places it is used in today. Because I just cann't see the waiting being necessary when you have far superior multiplexing technique to allow everybody to transmit at once with out worrying about collisions or interference.
Question 3
Doing Fourier series and the math out it is easy to see how to mathematically extract the data from the carrier or demodulate /modulate the data. But this is just on a piece of paper I am more fascinated or curious on what we can do with actually physically building these modulators/demodulators from the math.
I have built simple FM,AM transmitters / receivers over the years and I know the basics of how to create an oscillator , detector , tuner, ...etc circuit from simple resistors,caps,inductors...etc
But I am amazed that we can physically build all those modulators/demodulators circuits that you can do out on paper.
Curious from a hobby point of view is it possible to build detectors/modulators other then the simple ones with out special chips or hardware.
I know in theory you can do anything with enough cap , resistors,transistors, ...etc and enough space/time but I would think it would get to the point where it would take a life time to build these from simple electronic components/from scratch.
So is it true that other then the simple AM , FM transmitter/receivers the only reasonable way to create the more complex ones to send away for special QAM chips ,...other chips etc etc.
Though correct me if I am wrong
I know these questions are rather all over the place but my main one is if anybody knows more on why we use CSMA when we have all the multiplex things to never have collision issues. ( as well as if we use things like CDMA and other spread spectrum based multiplexing technique gives use are data security and prevents in most cases jamming signals)
Thanks for an info I hope you understand.
amp , phase , frequency ( digital are ASK , PSK ,FSK / analog versions are AM ,PM ,FM )
Most of the ones used are a combination of them like QAM 16,64,256 ,...etc as well as others.
I also know to have multiple people using a wireless or wired media at the same time you either have to do some sort of round robin or multiplexing technique.
For the round robin you could use CSMA avoidance/detection techniques or just a time slot.
If you want to transmit all people at the same time then you would have to do some multiplex technique like TDM ,FDM CDMA ,COCDMA , ...etc etc there are many choices but in principle they all use some form of time, amplitude , frequency , phase , use multiple carriers (i.e vary shape) and or combination of them to allow people to transmit all at the same time with no interference. (I know by doing the math which ones are better in which situations )
Channel based transmissions ones that are used in mobile phone networks MUST USE MULTPLEXING or then we would have chaos if a ton of people wanted to use it forget round robin or waiting.
But then we have Packet based based transmissions like the ones in 802.11 or ethernet home LANS. In these multiple people really cann't transmit all at once like the mobile phone network allows but they use CSMA detection/avoidance which usually a person wireless/wired card waits for the channel to be clear to send. Same thing when it comes to going out my cable internet modem.
I am curious why don't we just all use the multiplex techniques and stop using the CSMA stuff and use the multiplexing technique that allow us to have many people sending there data all at once. (i,e with no waiting to see if the channel is clear or other things)
Question 2
Is this sort of CSMA avoidance/detection / time slot info sending just used in the computer LAN and modems to the ISP. Or is there more places it is used in today. Because I just cann't see the waiting being necessary when you have far superior multiplexing technique to allow everybody to transmit at once with out worrying about collisions or interference.
Question 3
Doing Fourier series and the math out it is easy to see how to mathematically extract the data from the carrier or demodulate /modulate the data. But this is just on a piece of paper I am more fascinated or curious on what we can do with actually physically building these modulators/demodulators from the math.
I have built simple FM,AM transmitters / receivers over the years and I know the basics of how to create an oscillator , detector , tuner, ...etc circuit from simple resistors,caps,inductors...etc
But I am amazed that we can physically build all those modulators/demodulators circuits that you can do out on paper.
Curious from a hobby point of view is it possible to build detectors/modulators other then the simple ones with out special chips or hardware.
I know in theory you can do anything with enough cap , resistors,transistors, ...etc and enough space/time but I would think it would get to the point where it would take a life time to build these from simple electronic components/from scratch.
So is it true that other then the simple AM , FM transmitter/receivers the only reasonable way to create the more complex ones to send away for special QAM chips ,...other chips etc etc.
Though correct me if I am wrong
I know these questions are rather all over the place but my main one is if anybody knows more on why we use CSMA when we have all the multiplex things to never have collision issues. ( as well as if we use things like CDMA and other spread spectrum based multiplexing technique gives use are data security and prevents in most cases jamming signals)
Thanks for an info I hope you understand.
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