function [add_noise_LT, add_noise_NT] = evalNoise(f, NT_node, LT_node, ...
start_node, stop_node, tot_len, tot_Att , 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 disturbed modem        
%            LT_node   : LT node of disturbed 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
%								 (XTlevel.NEXT XTlevel.FEXT XTlevel.thirdCXT must have been assigned)
%
%            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:
%    FSAN duplex simulation memo, Telia 1998
%% ===========================================================================

%% ===========================================================================
% Copyright (C) 1998 by Telia Research AB, Lulea, Sweden; All rights reserved. 
% Project       : FSAN duplex model
% Author(s)     : Tomas Nordstrom (Tomas.B.Nordstrom@Telia.se)
%               : Daniel Bengtsson (Daniel.J.Bengtsson@Telia.se)
%
% CVS:       $Id: evalNoise.m,v 1.4 1999/03/31 13:15:54 tono Exp $
%% ===========================================================================
% 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
%% ===========================================================================
  
% --------------------------------
% Step 1: Generate noise in LT end  
% --------------------------------

%-----------------------------
% Step 1.1: NEXT from PSD_down              
%-----------------------------
tmp=zeros(size(f));
if NT_node<=start_node,
	len_att=NaN;   
elseif LT_node<stop_node,
   len_att=abs(tot_len(start_node)-tot_len(LT_node));
   att=-abs(tot_Att(start_node,:)-tot_Att(LT_node,:));
   dB_xtalk=XTlevel.NEXT+15*log10(f./1e6)+att;
   xtalk=10.^(dB_xtalk/10);
   tmp=xtalk.*PSD_down;
else
   len_att=NaN;
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);
   len_att=tot_len(stop_node)-tot_len(NT_node);
   if len_fext~=0,
      att=tot_Att(stop_node,:)-tot_Att(LT_node,:);
      dB_xtalk=XTlevel.FEXT+20.*log10(f/1e6)+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;
   len_att=0;
elseif (start_node<LT_node)&(stop_node<NT_node),
   len_fext=tot_len(stop_node)-tot_len(LT_node);
   len_att=0;
   if len_fext~=0,
      att=tot_Att(stop_node,:)-tot_Att(LT_node,:);
      dB_xtalk=XTlevel.FEXT+20.*log10(f/1e6)+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;
   len_att=0;      
elseif (LT_node<start_node)&(NT_node<stop_node),
   len_fext=tot_len(NT_node)-tot_len(start_node);
   len_att=tot_len(stop_node)-tot_len(NT_node)+tot_len(start_node)-tot_len(LT_node);
   if len_fext~=0,
      att=tot_Att(stop_node,:)-tot_Att(LT_node,:);
      dB_xtalk=XTlevel.FEXT+20.*log10(f/1e6)+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);
   len_att=tot_len(start_node)-tot_len(LT_node);
   if len_fext~=0,
      att=tot_Att(stop_node,:)-tot_Att(LT_node,:);
      dB_xtalk=XTlevel.FEXT+20.*log10(f/1e6)+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),
   len_att=tot_len(LT_node)-tot_len(stop_node);
   att=tot_Att(LT_node,:)-tot_Att(stop_node,:);
   dB_xtalk=XTlevel.thirdCXT+25.*log10(f/1e6)+att;
   xtalk=10.^(dB_xtalk/10);
   tmp=xtalk.*PSD_up;
end;
add_noise_LT.thirdCXT=tmp;

% ---------------------------------
% Step 2: Generate noise in NT end 
% --------------------------------

%---------------------------
% Step 2.1: NEXT from PSD_up
%---------------------------
tmp=zeros(size(f));
if (NT_node<=start_node)|(LT_node>=stop_node), % should this be there or not??
   len_att=NaN;
elseif NT_node>1,
   len_att=abs(tot_len(NT_node)-tot_len(stop_node)); 
   att=-abs(tot_Att(NT_node,:)-tot_Att(stop_node,:));
   dB_xtalk=XTlevel.NEXT+15*log10(f./1e6)+att;
   xtalk=10.^(dB_xtalk/10);
   tmp=xtalk.*PSD_up;
else
   len_att=NaN;
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);
   len_att=tot_len(LT_node)-tot_len(start_node);
   if len_fext~=0,
      att=tot_Att(NT_node,:)-tot_Att(start_node,:);
      dB_xtalk=XTlevel.FEXT+20.*log10(f/1e6)+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;
   len_att=0;
elseif (start_node<=LT_node)&(stop_node<NT_node),
   len_fext=tot_len(stop_node)-tot_len(LT_node);
   len_att=tot_len(NT_node)-tot_len(stop_node)+tot_len(LT_node)-tot_len(start_node);
   if len_fext~=0,
      att=tot_Att(NT_node,:)-tot_Att(start_node,:);
      dB_xtalk=XTlevel.FEXT+20.*log10(f/1e6)+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;
   len_att=0;
elseif (LT_node<start_node)&(NT_node<=stop_node),
   len_fext=tot_len(NT_node)-tot_len(start_node);
   len_att=0; %tot_len(stop_node)-tot_len(NT_node);
   if len_fext~=0,
      att=tot_Att(NT_node,:)-tot_Att(start_node,:);
      dB_xtalk=XTlevel.FEXT+20.*log10(f/1e6)+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,
 	len_att=tot_len(start_node)-tot_len(NT_node);
   att=tot_Att(start_node,:)-tot_Att(NT_node,:);
   dB_xtalk=XTlevel.thirdCXT+25.*log10(f/1e6)+att;
   xtalk=10.^(dB_xtalk/10);
   tmp=xtalk.*PSD_down;
end;
add_noise_NT.thirdCXT=tmp;