Help me calculate minimum SNR required

[peethol]

Hi,

I want to calculate the minimum SNR required,with modulation scheme (BPSK, QPSK or 8PSK) and a block code (LDPC or BCH), so that my system can work?
I've read in an article that NASA uses 11dB as their minimum SNR but I can't find the article anywhere and I can't remember what modulation scheme and FEC scheme they used.
So basically I want to know how would I calculate that minimum SNR value for a system?

Any help would be appreciated

 

[ashishchandra]

Re: Minimum SNR required

well to calculate min. SNR for different Digital modulation schemes first u need to know the data rate(Bandwidth) and type of modulation scheme from there u can get Eb/No (standard tables are available for different modulation schemes) after that simply multiply Eb/no with datarate and divide by bandwwidth after that u can add block code gain to get final Min. SNR.

 

[David83]

Re: Minimum SNR required

first of all you need the know or determine the BER required. Based on that, and knowing the modulation and coding scheme, you can find the minimum SNR required. However, in practical systems they add a margin over this minimum value for tolerance.

 

[elecstudward]

Re: Minimum SNR required

Hi,

I have a reference on te SNR requrement for different BER requirements for different modulation scheme. a page of 'Degrees of freedom in adaptive modulation' by A. Goldsmith is attached

I have a different issue on this area, I follow the equations as given in the paper, but the graph that i get is not the same ( i calculated for 16-QAM)

Here is the code i run in MATLAB:

k=4; % 4bits/symbol M=2^k >> 16QAM
SNR=[1:1000];SNRdb=10*log(SNR); % SNR/bit

BER4=0.2*exp(-1.6*SNR/(2^k-1));

ber=2*(1-1/sqrt(2^k))/k*erfc(sqrt(1.5*SNR/(2^k-1)));
figure(2);
semilogy(SNRdb,BER4);hold on;
semilogy(SNRdb,ber,'r*');grid on; axis([0 50 10^-8 1]);



Can anyone help me with this equation, i just don't know why they are not consistent...

Thank you