Value of M-Ary

communicationdatasimulation

Here, I want to simulate an M-ary [pulse-amplitude modulation] system. Anyhow, I chose my binary source to generate information at a rate of 1Mbps. The data "virtually" has a zero intersymbol interference (a.k.a zero ISI). If the channel of bandwidth 125 kHz. What is the minimum possible value of M? I found it like this:

M = 1 MBPS/125KHZ = 8 Bits

But the simulation fails to finish the work. But when I chose M=20, it works fine. Am I missing something here?


UPDATE:

Thanks everyone, I think I found the answer: Since we have:

\$ B_T = R_B/[2* log_2(M)]\$ ………(1)

Where:

\$ R_B\$ = Bit Rate = 1 MBPS ==> \$ R_B/2 = 500*10^3\$ symbols per second

\$ B_T\$ = The transmission bandwidth= \$125*10^3\$ symbols per second

So, substituting the values in equation (1) will lead us to know that the minimum value of M is 16.

Thank you everyone

Best Answer

This looks like homework, around here people are encouraged to learn from the experience of getting stuck.

You seem to be mixing up terms.

M = typically used to represent # of symbols and having zero ISI is a given, otherwise you've not chosen wisely. That is the point of constellation/trellis decoding system.

Your initial calculation should read 1 MBps = 125 KHz * 8 bits/symbol.

So the question is, why does a constellation of 20 symbols work when a constellation of 8 doesn't. Why isn't 20 a power of 2? Given that 20 fits into 5 bits what has happened to the other 12 symbols?

  • there are some hints in here...

But your question is also lacking, you're not explaining how you are simulating the system, what is meant by fails to "finish the work" etc.

You will need to clearer, more concise and reread/understand the basic theory before asking a more detailed question, with information and partial analysis. Please come back and update the question.