awgn.zip_Function awgn_matlab

function y=awgn(varargin) %AWGN Add white Gaussian noise to a signal. % Y = AWGN(X,SNR) adds white Gaussian noise to X. The SNR is in dB. % The power of X is assumed to be 0 dBW. If X is complex, then % AWGN adds complex noise. % % Y = AWGN(X,SNR,SIGPOWER) when SIGPOWER is numeric, it represents % the signal power in dBW. When SIGPOWER is 'measured', AWGN measures % the signal power before adding noise. % % Y = AWGN(X,SNR,SIGPOWER,STATE) resets the state of RANDN to STATE. % % Y = AWGN(..., POWERTYPE) specifies the units of SNR and SIGPOWER. % POWERTYPE can be 'db' or 'linear'. If POWERTYPE is 'db', then SNR % is measured in dB and SIGPOWER is measured in dBW. If POWERTYPE is % 'linear', then SNR is measured as a ratio and SIGPOWER is measured % in Watts. % % Example 1: % % To specify the power of X to be 0 dBW and add noise to produce % % an SNR of 10dB, use: % X = sqrt(2)*sin(0:pi/8:6*pi); % Y = awgn(X,10,0); % % Example 2: % % To specify the power of X to be 3 Watts and add noise to % % produce a linear SNR of 4, use: % X = sqrt(2)*sin(0:pi/8:6*pi); % Y = awgn(X,4,3,'linear'); % % Example 3: % % To cause AWGN to measure the power of X and add noise to % % produce a linear SNR of 4, use: % X = sqrt(2)*sin(0:pi/8:6*pi); % Y = awgn(X,4,'measured','linear'); % % See also WGN, RANDN, and BSC. % Copyright 1996-2008 The MathWorks, Inc. % $Revision: 1.9.4.6 $ $Date: 2008/08/22 20:23:43 $ % --- Initial checks error(nargchk(2,5,nargin,'struct')); % --- Value set indicators (used for the string flags) pModeSet = 0; measModeSet = 0; % --- Set default values sigPower = 0; pMode = 'db'; measMode = 'specify'; state = []; % --- Placeholder for the signature string sigStr = ''; % --- Identify string and numeric arguments for n=1:nargin if(n>1) sigStr(size(sigStr,2)+1) = '/'; end % --- Assign the string and numeric flags if(ischar(varargin{n})) sigStr(size(sigStr,2)+1) = 's'; elseif(isnumeric(varargin{n})) sigStr(size(sigStr,2)+1) = 'n'; else error('comm:awgn:InvalidArg','Only string and numeric arguments are allowed.'); end end % --- Identify parameter signatures and assign values to variables switch sigStr % --- awgn(x, snr) case 'n/n' sig = varargin{1}; reqSNR = varargin{2}; % --- awgn(x, snr, sigPower) case 'n/n/n' sig = varargin{1}; reqSNR = varargin{2}; sigPower = varargin{3}; % --- awgn(x, snr, 'measured') case 'n/n/s' sig = varargin{1}; reqSNR = varargin{2}; measMode = lower(varargin{3}); measModeSet = 1; % --- awgn(x, snr, sigPower, state) case 'n/n/n/n' sig = varargin{1}; reqSNR = varargin{2}; sigPower = varargin{3}; state = varargin{4}; % --- awgn(x, snr, 'measured', state) case 'n/n/s/n' sig = varargin{1}; reqSNR = varargin{2}; measMode = lower(varargin{3}); state = varargin{4}; measModeSet = 1; % --- awgn(x, snr, sigPower, 'db|linear') case 'n/n/n/s' sig = varargin{1}; reqSNR = varargin{2}; sigPower = varargin{3}; pMode = lower(varargin{4}); pModeSet = 1; % --- awgn(x, snr, 'measured', 'db|linear') case 'n/n/s/s' sig = varargin{1}; reqSNR = varargin{2}; measMode = lower(varargin{3}); pMode = lower(varargin{4}); measModeSet = 1; pModeSet = 1; % --- awgn(x, snr, sigPower, state, 'db|linear') case 'n/n/n/n/s' sig = varargin{1}; reqSNR = varargin{2}; sigPower = varargin{3}; state = varargin{4}; pMode = lower(varargin{5}); pModeSet = 1; % --- awgn(x, snr, 'measured', state, 'db|linear') case 'n/n/s/n/s' sig = varargin{1}; reqSNR = varargin{2}; measMode = lower(varargin{3}); state = varargin{4}; pMode = lower(varargin{5}); measModeSet = 1; pModeSet = 1; otherwise error('comm:awgn:InvalidSyntax','Syntax error.'); end % --- Parameters have all been set, either to their defaults or by the values passed in, % so perform range and type checks % --- sig if(isempty(sig)) error('comm:awgn:NoInput','An input signal must be given.'); end if(ndims(sig)>2) error('comm:awgn:InvalidSignalDims','The input signal must have 2 or fewer dimensions.'); end % --- measMode if(measModeSet) if(~strcmp(measMode,'measured')) error('comm:awgn:InvalidSigPower','The signal power parameter must be numeric or ''measured''.'); end end % --- pMode if(pModeSet) switch pMode case {'db' 'linear'} otherwise error('comm:awgn:InvalidPowerType','The signal power mode must be ''db'' or ''linear''.'); end end % -- reqSNR if(any([~isreal(reqSNR) (length(reqSNR)>1) (isempty(reqSNR))])) error('comm:awgn:InvalidSNR','The signal-to-noise ratio must be a real scalar.'); end if(strcmp(pMode,'linear')) if(reqSNR<=0) error('comm:awgn:InvalidSNRForLinearMode','In linear mode, the signal-to-noise ratio must be > 0.'); end end % --- sigPower if(~strcmp(measMode,'measured')) % --- If measMode is not 'measured', then the signal power must be specified if(any([~isreal(sigPower) (length(sigPower)>1) (isempty(sigPower))])) error('comm:awgn:InvalidSigPower','The signal power value must be a real scalar.'); end if(strcmp(pMode,'linear')) if(sigPower<0) error('comm:awgn:InvalidSigPowerForLinearMode','In linear mode, the signal power must be >= 0.'); end end end % --- state if(~isempty(state)) if(any([~isreal(state) (length(state)>1) (isempty(state)) any((state-floor(state))~=0)])) error('comm:awgn:InvaildState','The State must be a real, integer scalar.'); end end % --- All parameters are valid, so no extra checking is required % --- Check the signal power. This needs to consider power measurements on matrices if(strcmp(measMode,'measured')) sigPower = sum(abs(sig(:)).^2)/length(sig(:)); if(strcmp(pMode,'db')) sigPower = 10*log10(sigPower); end end % --- Compute the required noise power switch lower(pMode) case 'linear' noisePower = sigPower/reqSNR; case 'db' noisePower = sigPower-reqSNR; pMode = 'dbw'; end % --- Add the noise if(isreal(sig)) opType = 'real'; else opType = 'complex'; end y = sig+wgn(size(sig,1), size(sig,2), noisePower, 1, state, pMode, opType);