function [SumSNR]=calcFoldedSNR(SNR,f,fsym);
%% ===========================================================================
% calc_fold_SNR - Calculates the folded SNR for DFE-based
%                 PAM-margin calculation also applicable for not
%                 equally spaced f-axis
%
% Parameter:    SNR   	Signal to Noise ratio as simple Rx/Noise expression
% Parameter:    f	Frequency axis
% Parameter:    fsym	Symbol transmission rate
%
% Returns:      SumSNR	Folded SNR in dB
%
% Reference: 	T1E1.4/2000-002R2 DRAFT ANSI T1.XXX-2000
%
%% ===========================================================================

%% ===========================================================================
% Copyright (C) 2000 by Forschungszentrum Telekommunikation Wien, Austria;
%                                                     All rights reserved. 
% Project       : FSAN duplex model
% Author(s)     : Tomas Nordstrom (Tomas.Nordstrom@FTW.at)
%               : Gernot Schmid (schmid@ftw.at)
%
%% ===========================================================================
% Change History
%      2000-05-30 (GS)   Created
%      2000-06-20 (ToNo) Cleaning up  
%      2000-07-11 (ToNo) Made it use the new way of interpolation
%% ===========================================================================

% Generate a new f scale     
deltaf=100;
fnew=[deltaf:deltaf:fsym+1-deltaf];
fnewinv=fsym-fnew;

% Get the folds
SNR0  =      interp1(f,SNR,fnew,'linear');
SNR1  =      interp1(f,SNR,fnew+fsym,'linear');
SNRm1 = conj(interp1(f,SNR,fnewinv,'linear'));
SNRm2 = conj(interp1(f,SNR,fnewinv+fsym,'linear'));

% Sum the folds
folded_SNR=SNR0+SNR1+SNRm1+SNRm2;

SumSNR=trapz(fnew,10*log10(1+folded_SNR))/fsym;