Hello,
I am (still) doing a university class on all sorts of stuff including networking, where the explanations are suboptimal. I would like to ask you to answer these questions in the simplest manner as possible.
So a few questions first.
Frequencies:
The way I understand frequencies, we have electromagnetic waves and the frequency describes how often the amplitude goes up and down. So for example, 2.4GHz (or rather 2.4GHz - 2.5GHz) describes a bandwidth where the waves go up and down in a interval within a time frame (the speed is 2.4GHz - 2.5 GHz).
Now what I don't quite understand is: How do devices work with frequencies. Let's just pretend there is two devices in the world that use frequencies.
Obviously I have things like FSK, ASK and PSK (which I ironically understand, or I think I do) as forms of modulation in . The devices need some form of modulation to write the signals on the medium they use: These methods of modulation mean that amplitude is "manipulated" and thus the "appropriate electromagnetic waves" are generated (?) to send the signals.
In simple terms, how does this work? When I send via WLAN or mobile does my mobile phone manipulate amplitude to generate electromagnetic waves to send data? If that is correct - how does my phone know what frequency to listen to when receiving data?
As for FSK - when my mobile phone is sending within a frequency range, lower frequency means sending 0s while higher frequency means writing 1s. Is the "lower" and "higher" frequency just relative to the frequency range my phone communicates in?
The way I understand this is when communicating with an access point the devices communicate within a certain frequency band (bandwidth). So to write 0s I'd have to use lower frequencies within that range?
(My study materials really just say about FSK that lower frequency = 0, higher = 1 and I am desperately trying to make sense of it without going into phyiscs too hard)
Channels:
What do people mean by channel in this entire context? The only thing I sort of think I know is that channels dont actually exist but they are some sort of logical unit because data packets (see IP-Packets) are not that big and given a big enough frequency range we could split that frequency range up into multiple channels to send data packets simultaneously. So what's a channel?
Bandwidth:
Bandwidth generally describes the range between a lower and a upper frequency. How this would work for wireless I understand because we already use frequencies, but what about cable? Does the frequency range determine how many data frames we can send within a time unit?
I also "understood" that the higher bandwidth, the more "channels" we have
Multiplexing:
FDMA: I read conflicting things about FDMA on the internet really. On one side it says that FDMA means that one signal station (cell tower for example) has a frequency range and it splits it up into smaller frequency ranges which can be used by one device at a time. -> Do I have to think of this as: Users don't occupy one of the "smaller frequency ranges" of the all the time but they use vacant ones when they need to transmit data?
Other sources I've read say that frequency multiplexing means that one device can use multiple frequencies to increase data throughput. -> The only way I can make sense of this is that one device transmits data on one of the "smaller frequency ranges" and within that multiple channels are used
Which one is it then?
SDMA: Here I've also read conflicting descriptions. One one side it says that SDMA means the use one dedicated medium to transmit data. The way I understand this is that SDMA would simply be using different cables or splitting free space up into different cells.
Other sources I've read say that this describes the parallel use of multiple channels. What do they mean by that?
And what do they mean by channel in the context of multiplexing?
I know these are a lot of questions. I'd be happy if I could have at least one of them answered so someone whose brain operates with a hamster wheel understands.
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