5dbc48abc0
Current work is on MLSE and SD Decoding etc. MLSE is currently not 100% working, the scalings are maybe off?!
94 lines
2.5 KiB
Matlab
94 lines
2.5 KiB
Matlab
function [GMI,NGMI] = calc_gmi_bitwise(test_signal,reference_signal,options)
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% https://cioffi-group.stanford.edu/doc/book/AppendixG.pdf
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arguments(Input)
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test_signal;
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reference_signal;
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options.skip_front = 0;
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options.skip_end = 0;
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options.returnErrorLocation = 0;
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end
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options.skip_end = abs(options.skip_end);
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options.skip_front = abs(options.skip_front);
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assert((options.skip_end+options.skip_front)<length(test_signal),"You can not skip more bits than overall length of data! Set skip_front or skip_end to lower value or check data_in");
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if isa(reference_signal,'Signal')
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reference_signal = reference_signal.signal;
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end
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if isa(test_signal,'Signal')
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test_signal = test_signal.signal;
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end
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% TRIM
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[test_signal,reference_signal]=trimseq(test_signal,reference_signal,options.skip_front,options.skip_end);
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% CALC AIR
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%%% new implementation of AIR
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% Precompute
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N = length(test_signal);
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M = numel(unique(reference_signal));
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nBits = log2(M);
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levels = PAMmapper(M,0).levels / PAMmapper(M,0).scaling;
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grayBits= PAMmapper(M,0).showBitMapping;
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priors = ones(1,M)/M;
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noise = test_signal-reference_signal;
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sigma2 = var(noise);
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% Allocate
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LLR = zeros(N, nBits);
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rxBits = zeros(N, nBits);
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for n = 1:N
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y = test_signal(n);
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ll_table= -((y - levels).^2)/(2*sigma2) + log(priors); % M×1
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% Per‐bit LLR
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for b = 1:nBits
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idx0 = grayBits(:,b)==0;
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idx1 = grayBits(:,b)==1;
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L0 = logsumexp(ll_table(idx0));
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L1 = logsumexp(ll_table(idx1));
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LLR(n,b) = L1 - L0;
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end
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end
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tx_bits = PAMmapper(M,0,"eth_style",0).demap(reference_signal);
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% Compute GMI (bit‐wise MI averaged over all symbols)
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MI_bits = zeros(1,nBits);
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for b = 1:nBits
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r0 = LLR(tx_bits(:,b)==0,b);
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r1 = LLR(tx_bits(:,b)==1,b);
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I0 = mean( log2(1 + exp(r0)) );
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I1 = mean( log2(1 + exp( -r1)) );
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MI_bits(b) = 1 - 0.5*(I0 + I1);
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end
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GMI = sum(MI_bits); % in bits per symbol
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NGMI = GMI / nBits; % normalized per bit
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% Auxiliary nested helper for numerically stable log-sum-exp
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function s = logsumexp(a)
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% LOGSUMEXP Compute log(sum(exp(a))) in a numerically stable way
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m = max(a);
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s = m + log(sum(exp(a - m)));
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end
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function [data_,reference_]=trimseq(data,reference,skipstart,skip_end)
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data_ = data(skipstart+1:end-skip_end,:);
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delta_bits = length(reference) - length(data);
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skip_end = delta_bits + skip_end;
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reference_ = reference(skipstart+1:end-skip_end,:);
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end
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end |