Im' trying to build a big picture of telecommunication and i'm stuck in a topic, related to digital communication. But the problem is that i can't go too deep into the topic because it is imensely huge and due to time constraint, so i'm trying to get an informal and intuitive big-picture ( but as accurate as i can ).
From what i could read, we can think informally that the probability error is dependant solely on two things :
1 - SNR
2 - Our channel codec ( coder-decoder )
If we implement a better channel codec, we need to pay less SNR for the same probability error.
And also from not-to-deep research, i could pin that SNR would be solely dependant on 2 things :
1 - Signal power at the receiver. This is mainly dependant on our channel characteristics regarding path loss , on the desired bit rate ( which dictates the bandwidth required ) and on the delivered signal power at the transmitter.
2 - Noise power at the receiver. This is mainly dependant on our channel noise resistance ( how prone the channel is to all kinds of internal noises and external noises ), quantization noise, ISI,etc.
My first question :
I - Apart from the perharps informal and vague treatise, is there some major thing i'm missing on the picture or is there some major thing i have a misconception ?
The second question is :
II - I have read in a text-book that on a digital communication system with A/D step, SNR is directly proportional to the number M of quantization levels :
This makes total sense because by increasing M, we end-up decreasing the quantization noise and hence decreasing the noise power at the output. By decreasing the noise power at the output, we would increase SNR.
But i'm thinking here that whenever we increase M, we are actually increasing the bit-rate ( with M=128, each symbol is worth 5 bits but with M=256 each symbol is worth 6 bits,so for the same symbol rate, we need to increase the bit rate ) , and hence decreasing the signal power at the output ( because of a higher bandwidth required ) and hence decreasing SNR.
So, to me, increasing M would not necessarily increase SNR as my text-book says...
Is my reasoning correct ?
So these are my only two questions. Thanks a lot in advance.