%CALCSNRS calculates the signal to noise ratio in each subchannel.% [Si,Mi,Ui,Ni,Ci,Ii] = CALCSNRS(Sx,H,Sn,G) returns the SNRs in Si and the % matched filter bound in the used subchannels in Mi. The used channel are% those which can support at least 2 bits with the given SNR gap in G.% The used channels are returned in Ui, the used noise spectrum in Ni, the% used channel gains in Ci and the used input spectrum in Ii.% % Sx is the raw input power spectrum, H the channel gain squared, Sn% the channel noise power spectrum and G the snr gap in dB.% Copyright (c) 1999-2003 The University of Texas% All Rights Reserved.%  % This program is free software; you can redistribute it and/or modify% it under the terms of the GNU General Public License as published by% the Free Software Foundation; either version 2 of the License, or% (at your option) any later version.%  % This program is distributed in the hope that it will be useful,% but WITHOUT ANY WARRANTY; without even the implied warranty of% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the% GNU General Public License for more details.%  % The GNU Public License is available in the file LICENSE, or you% can write to the Free Software Foundation, Inc., 59 Temple Place -% Suite 330, Boston, MA 02111-1307, USA, or you can find it on the% World Wide Web at http://www.fsf.org.%  % Programmers:	Guner Arslan% Version:        %W% %G%% % The authors are with the Department of Electrical and Computer% Engineering, The University of Texas at Austin, Austin, TX.% They can be reached at arslan@ece.utexas.edu.% Guner Arslan is also with the Embedded Signal Processing% Laboratory in the Dept. of ECE, http://signal.ece.utexas.edu.function [initSNRi,MFBi,usedChannels,noiseSpec,channelGain,inputSpec] = ...   calcsnrs(initInputSpec,initChannelGain,initNoiseSpec,gamma)N = (length(initInputSpec)-1)*2;%calculate SNRi for Sx = 1;initSNRi = initInputSpec.*initChannelGain./initNoiseSpec; %Eliminate useless channels, first assume all usable channelsusedChannels = ones(1,N/2+1) == 1;%SNR required to carry 2 bits with given gapSNR2bits = gamma*(2^2-1);%Do not use subchannels which cannot carry 2 bits%usedChannels = initSNRi >= SNR2bits;%Do not use DC and Nyquist subchannelsusedChannels(1) = 0;usedChannels(N/2+1) = 0;%Do not use POTS bandusedChannels(2:6) = 0;if sum(usedChannels) == 0    warning('Not enough transmit power to transmit any bits through the channel');    warning('RESULTS ARE NOT VALID');    usedChannels(1) = 1;end%noise and channel gain in used channels noiseSpec = initNoiseSpec(usedChannels);channelGain = initChannelGain(usedChannels);inputSpec = initInputSpec(usedChannels);%matched filter bound if available power would be distributed %over the entire bandwidthMFBi = inputSpec.*channelGain./noiseSpec;%MFBiall = initInputSpec.*initChannelGain./initNoiseSpec;