function [add_noise_LT, add_noise_NT] = evalNoise(f, NT_node, LT_node, ...
start_node, stop_node, tot_len, Att_mtr, PSD_up, PSD_down, XTlevel)
%% ===========================================================================
%evalNoise - Calculates noise in LT and NT nodes from disturber in
%            start to stop node PSD_up and PSD_down disturbers PSD masks
%
%            INPUT 
%            ------
%            f         : Frequency axis
%            NT_node   : NT node of victim modem        
%            LT_node   : LT node of victim modem    
%            start_node: LT node of disturber
%            stop_node : NT node of disturber
%            tot_len   : Length vector, 
%                        tot_len(n)=distance to node n from the first node    
%            tot_Att   : Attenuation model in dB/km matrix
%            PSD_up    : Disturber PSD transmitted from NT end
%            PSD_down  : Disturber PSD transmitted from LT end
%            XTlevel   : structure that contains NEXT,FEXT,thirdCXT values
%
%            OUTPUT
%            -------
%            add_noise_LT(.NEXT .FEXT .thirdCXT): Noise to be added in LT end
%            add_noise_NT(.NEXT .FEXT .thirdCXT): Noise to be added in NT end
%
% Example(s):
%   
%
% Algorithmic details:
%    Step 1:          Calculate noise in LT end         
%        Step 1.1:    NEXT from PSD_down
%        Step 1.2:    FEXT from PSD_up
%	 Step 1.3:    3CXT from PSD_up
%        
%    Step 2:          Calculate noise in NT end         
%        Step 2.1:    NEXT from PSD_up
%        Step 2.2:    FEXT from PSD_down
%        Step 2.3:    3CXT from PSD_down
%        
%
% Reference:
%    FTW's xDSLsimu manual
%% ===========================================================================

%% ===========================================================================
% Copyright (C) 1998-1999 by Telia Research AB, Lulea, Sweden; 
%               2000-2009 by Forschungszentrum Telekommunikation Wien, Austria;
%                                                         All rights reserved.
% Project       : FTW's xDSLsimu
% Author(s)     : Tomas Nordstrom (Tomas.Nordstrom@FTW.at)
%               : Daniel Bengtsson (Daniel.J.Bengtsson@Telia.se)
%               : Bo Engstrom (bosse@upzide.com)
%
% CVS:       $Id: evalNoise.m 752 2009-01-02 13:03:52Z tono $
%% ===========================================================================
% Change History
%      1998-12-16 (DaB)	 Created      	 
%      1998-12-22 (ToNo) Added and updated comments
%      1999-01-08 (DaB) Bug fixed in DS FEXT
%      1999-01-12 (DaB) Fixed bug in US NEXT 
%      1999-02-04 (DaB) Multiple cables allowed
%      1999-02-04 (DaB) added input parameter to control 
%                       XTlevel (NEXT,FEXT,thirdCXT)
%      1999-02-04 (DaB) Added 3CXT noise
%      1999-02-09 (DaB) Fixed NEXT FEXT thirdCXT add bug
%      1999-03-10 (DaB) Rewritten to optimize speed
%      1999-03-30 (DaB) Bug correction
%      1999-08-11 (DaB) Updated for Bridgetap calc
%      2001-06-19 (Bosse) Octave port
%      2001-07-01 (PeKa) Octave to Matlab compatibility port
%      2001-09-11 (ToNo) Added support for "4 order" NEXT term
%      2001-10-08 (ToNo) Made "4 order" NEXT flag global,
%                        and made some editorial changes.
%      2001-12-05 (ToNo) Fixed 4-order term to be |H|^2^2 instead of |H|^2^4
%      2002-08-01 (ToNo) Speed things up by reducing duplicated calculations
%      2003-11-03 (ToNo) Lists now use cell arrays for both Octave and Matlab
%      2005-07-10 (ToNo) Implemented non-standard slanting for NEXT and FEXT
%                        Cleaned up unused conditions, a variable, and comments
%% ===========================================================================

f1MHz = f./1e6;
log10f1MHz = log10(f1MHz);

x25log10f1MHz = 25.*log10f1MHz; % Hard coded 3cXT slant

% --------------------------------
% Step 1: Generate noise at the LT end  
% --------------------------------

%-----------------------------
% Step 1.1: NEXT from PSD_down              
%-----------------------------

tmp=zeros(size(f));
if (NT_node>start_node) && (LT_node<stop_node),
    if start_node>LT_node,
        att=Att_mtr{LT_node,start_node};
        if NT_node>stop_node,      % Determine the common loop att
            attL=Att_mtr{start_node,NT_node};
        else
	    attL=Att_mtr{start_node,stop_node};
        end
    else
        att=Att_mtr{start_node,LT_node};
        if NT_node>stop_node,      % Determine the common loop att
            attL=Att_mtr{LT_node,NT_node};
        else
	    attL=Att_mtr{LT_node,stop_node};
        end
    end;

    if XTlevel.NEXTx4,
        dB_xtalk=XTlevel.NEXT+...
                 XTlevel.NEXTslant*log10f1MHz+ ...
                 10*log10(1-10.^(2*attL/10))+att;
    else
        dB_xtalk=XTlevel.NEXT+XTlevel.NEXTslant.*log10f1MHz+att;
    end;
    xtalk=10.^(dB_xtalk/10);
    tmp=xtalk.*PSD_down;
end;  % if
add_noise_LT.NEXT=tmp;

%---------------------------
% Step 1.2: FEXT from PSD_up
%---------------------------
tmp=zeros(size(f));
if (LT_node>=start_node)&&(NT_node<=stop_node),
    len_fext=tot_len(NT_node)-tot_len(LT_node);
    if len_fext~=0,
        att=Att_mtr{LT_node,stop_node};
        dB_xtalk=XTlevel.FEXT+XTlevel.FEXTslant.*log10f1MHz+...
                 10.*log10(len_fext)+att;
        xtalk=10.^(dB_xtalk/10);
        tmp=xtalk.*PSD_up;
    end; % if
elseif (start_node<LT_node)&&(stop_node<=LT_node),
    len_fext=0;
elseif (start_node<LT_node)&&(stop_node<NT_node),
    len_fext=tot_len(stop_node)-tot_len(LT_node);
    if len_fext~=0,
        att=Att_mtr{LT_node,stop_node};
        dB_xtalk=XTlevel.FEXT+XTlevel.FEXTslant.*log10f1MHz+...
                 10.*log10(len_fext)+att;
        xtalk=10.^(dB_xtalk/10);
        tmp=xtalk.*PSD_up;
    end; % if
elseif (LT_node<start_node)&&(NT_node<=start_node),
    len_fext=0;
elseif (LT_node<start_node)&&(NT_node<stop_node),
    len_fext=tot_len(NT_node)-tot_len(start_node);
    if len_fext~=0,
        att=Att_mtr{LT_node,stop_node};
        dB_xtalk=XTlevel.FEXT+XTlevel.FEXTslant.*log10f1MHz+...
                 10.*log10(len_fext)+att;
        xtalk=10.^(dB_xtalk/10);
        tmp=xtalk.*PSD_up;
    end; %if   
    
elseif (LT_node<=start_node)&&(stop_node<=NT_node),
    len_fext=tot_len(stop_node)-tot_len(start_node);
    if len_fext~=0,
        att=Att_mtr{LT_node,stop_node};
        dB_xtalk=XTlevel.FEXT+XTlevel.FEXTslant.*log10f1MHz+...
                 10.*log10(len_fext)+att;
        xtalk=10.^(dB_xtalk/10);
        tmp=xtalk.*PSD_up;
    end; %if   

end;  %if   
add_noise_LT.FEXT=tmp;
%----------------------------
% Step 1.3 3CXT from PSD_up
%----------------------------
tmp=zeros(size(f));
if (stop_node<=LT_node),
    att=Att_mtr{stop_node,LT_node};
    dB_xtalk=XTlevel.thirdCXT+x25log10f1MHz+att;
    xtalk=10.^(dB_xtalk/10);
    tmp=xtalk.*PSD_up;
end;
add_noise_LT.thirdCXT=tmp;

% ---------------------------------
% Step 2: Generate noise at the NT end 
% --------------------------------

%---------------------------
% Step 2.1: NEXT from PSD_up
%---------------------------
tmp=zeros(size(f));
if (NT_node>start_node) && (LT_node<stop_node),
    if NT_node>stop_node,
        att=Att_mtr{stop_node,NT_node};
        if LT_node>start_node,                 % Determine the common loop att
            attL=Att_mtr{LT_node,stop_node};
        else
	    attL=Att_mtr{start_node,stop_node};
        end
    else
        att=Att_mtr{NT_node,stop_node};
        if LT_node>start_node,                 % Determine the common loop att
            attL=Att_mtr{LT_node,NT_node};
        else
	    attL=Att_mtr{start_node,NT_node};
        end
    end;
    if XTlevel.NEXTx4,
        dB_xtalk=XTlevel.NEXT+...
                 XTlevel.NEXTslant.*log10f1MHz+ ...
                 10*log10(1-10.^(2*attL/10))+att;
    else
        dB_xtalk=XTlevel.NEXT+XTlevel.NEXTslant.*log10f1MHz+att;
    end
    xtalk=10.^(dB_xtalk/10);
    tmp=xtalk.*PSD_up;
end; %if
add_noise_NT.NEXT=tmp;

%-----------------------------
% Step 2.2: FEXT from PSD_down
%-----------------------------
tmp=zeros(size(f));
if (LT_node>=start_node)&&(NT_node<=stop_node), 
    len_fext=tot_len(NT_node)-tot_len(LT_node);
    if len_fext~=0,
        att=Att_mtr{start_node,NT_node};
        dB_xtalk=XTlevel.FEXT+XTlevel.FEXTslant.*log10f1MHz+...
                 10.*log10(len_fext)+att;
        xtalk=10.^(dB_xtalk/10);
        tmp=xtalk.*PSD_down;
    end; %if   
elseif (start_node<LT_node)&&(stop_node<=LT_node)
    len_fext=0;
elseif (start_node<=LT_node)&&(stop_node<NT_node),
    len_fext=tot_len(stop_node)-tot_len(LT_node);
    if len_fext~=0,
        att=Att_mtr{start_node,NT_node};
        dB_xtalk=XTlevel.FEXT+XTlevel.FEXTslant.*log10f1MHz+...
                 10.*log10(len_fext)+att;
        xtalk=10.^(dB_xtalk/10);
        tmp=xtalk.*PSD_down;
    end; %if      
elseif (LT_node<start_node)&&(NT_node<start_node),
    len_fext=0;
elseif (LT_node<start_node)&&(NT_node<=stop_node),
    len_fext=tot_len(NT_node)-tot_len(start_node);
    if len_fext~=0,
        att=Att_mtr{start_node,NT_node};
        dB_xtalk=XTlevel.FEXT+XTlevel.FEXTslant.*log10f1MHz+...
                 10.*log10(len_fext)+att;
        xtalk=10.^(dB_xtalk/10);
        tmp=xtalk.*PSD_down;
    end; %if 
end;  %if   
add_noise_NT.FEXT=tmp;

%-----------------------------
% Step 2.3: 3CXT from PSD_down
%-----------------------------
tmp=zeros(size(f));
if NT_node<=start_node,
    att=Att_mtr{NT_node,start_node};
    dB_xtalk=XTlevel.thirdCXT+x25log10f1MHz+att;
    xtalk=10.^(dB_xtalk/10);
    tmp=xtalk.*PSD_down;
end;
add_noise_NT.thirdCXT=tmp;