function noise_floor = get_noise_floor(f, L, ISDN)
%% ===========================================================================
%get_noise_floor - Function to provide noise floor for FDD ADSL simulations.
%
% Parameter:    f       Vector of frequencies, in Hz, 
%                       at which noise floor values are desired
%               L       Loop length, in m, of main branch of the test loop
%               ISDN    Flag to indicate whether to generate POTS or ISDN 
%                       noise floor; set to 1 for ISDN
%
% Returns:      noise_floor	Noise floor in dBm/Hz
% Example(s):
%
% Algorithmic details:
%
% Reference:
%   ETSI TM6 WD??
%% ===========================================================================

%% ===========================================================================
% Copyright (C) 2001-2003 by Forschungszentrum Telekommunikation Wien, Austria;
%                                                     All rights reserved. 
% Description   : ADSL performance simulations
%
% Project       : FTW's xDSLsimu
% Author(s)     : Krista Jacobsen (Jacobsen@ti.com)
%                 Tomas Nordstrom (Tomas.Nordstrom@FTW.at)
%
% CVS:       $Id: get_noise_floor.m,v 3.1 2002/12/27 15:56:06 tono Exp $
%% ===========================================================================
% Change History
%      2001-09-21 (KJ)   Created
%      2001-10-08 (ToNo) Moved it into the simulator and added comments
%% ===========================================================================

f=f./1e3; % Below we use kHz
L=L./1e3; % and km

if ISDN,
    indices = find (f < 500);  
    if (L < 4),
        noise_floor = (-120-5*L) * ones(size(f)); % This is the flat part of the PSD
        noise_floor(indices) = -114 - 6*log(f(indices)/250)/log(2) - 5*L;
    else	% L >= 4km,
        noise_floor = -140*ones(size(f));
        noise_floor(indices) = -134 - 6*log(f(indices)/250)/log(2);
    end;	% if (L < 4),
else,
    indices = find(f < 250);
    if (L < 4),
        noise_floor = (-120-5*L) * ones(size(f)); % This is the flat part of the PSD
        noise_floor(indices) = -114 - 6*log(f(indices)/125)/log(2) - 5*L;
    else	% L >= 4km,
        noise_floor = -140*ones(size(f));
        noise_floor(indices) = -134 - 6*log(f(indices)/125)/log(2);
    end;	% if (L < 4),
end;	% if ISDN,