function B = getBFromIL(cablemodel,f,Zterm,d)
%% ===========================================================================
% getBFromInserLoss - Get the "B" parameter from insertion loss of splitter,
%                     where B is a parameter of transmisson line 
%                     given by an "ABCD" or "two-port modeling" theory
%                     (A=D=1, C=0).
%
% Parameter:    cablemodel      Cable model structure
%               cablemodel.param.ffile  Filename containing the frequencies    
%               cablemodel.param.ilfile Filename containing the IL values
%               f	        Frequency axis
%               Zterm           Load impedance
%               d               Cable length in km
%                                 If d>1/1000 we asssume a length dependence    
%                                    d<= we assume no length
%                                        dependence (e.g. a splitter)
% Returns:      B               The resulting B(f) vector 
%
% Example(s):
% Reference:
%		
%% ===========================================================================

%% ===========================================================================
% Copyright (C):
%       2000-2009 by Forschungszentrum Telekommunikation Wien, Austria;
%                                                         All rights reserved.
% Project       : FTW's xDSLsimu
% Author(s)     : Driton Statovci(statovci@ftw.at)
%               : Tomas Nordstrom (Tomas.Nordstrom@FTW.at)
%% ===========================================================================
% Change History
%      2000-11-20 (DrSt)  Created
%      2001-02-22 (ToNo)  Modified to read from a file for data
%      2008-08-27 (ToNo)  Modified when length dependance kicks in
%% ===========================================================================

% We assume
Zs=Zterm; % Source impedance
Zl=Zterm; % Load impedance

% Get the data pointed to by the cable model
if isfield(cablemodel.param, 'ffile'),
  ftmp   = load(cablemodel.param.ffile);
  Tiltmp = load(cablemodel.param.ilfile); % Insertion loss from file, in [dB]
else
  ftmp   = cablemodel.param.ftab;
  Tiltmp = cablemodel.param.iltab;  % Insertion loss from data field, in [dB]    
end;

% Insertion loss interpolation 
method ='linear';
Til    = interp1(ftmp,Tiltmp, f, method);

% If the length is greater than one meter we assume a length dependence
if d>1/1000
    Til = Til*d;
end;

% Convert IL onto B
T = 10.^(Til/20);
B = (Zl+Zs)*(1 - T)./T;