estnoisepower.m

阵列信号处理的工具箱

function noisePowerOut = estnoisepower(sigIn, dispOpt, noSrc)

%ESTNOISEPOWER Estimate noise power of a radar signal.
%
%--------
%Synopsis:
%  noisePowerOut = estnoisepower(sigIn)
%  noisePowerOut = estnoisepower(sigIn, dispOpt)
%  noisePowerOut = estnoisepower(sigIn, dispOpt, noSrc)
%
%Description:
%  Estimate noise power of a radar signal. As the estimed power, the mean
%  value of the smallest eigenvalues of the spatial correlation matrix 
%  for the first range bin, first CPI and first trial is taken.
%
%Output and Input:
%  noisePowerOut (RealScalarT): Estimated noise power.
%  sigIn (RxRadarSigT or RxCorrMatT): Input radar signal or correlation matrix.
%  dispOpt [D](StringT): Display options.
%    = 'n': Don't print on screen.
%    = 'p': Print on screen.
%  noSrc [D](IntScalarT): Number of signal sources. This means that there
%    are ((number-of-channels) - noSrc) noise eigenvalues. If this value
%    is too low, the estimated noise power will be somewhat too low. If
%    this value is too high, the estimated noise power will be too high
%    (maybe much too high). Default value is = 1, which means that only the
%    smallest eigenvalue is used.
%
%--------
%Notations:
%  Data type names are shown in parentheses and they start with a capital
%  letter and end with a capital T. Data type definitions can be found in [1]
%  or by "help dbtdata".
%  [D] = This parameter can be omitted and then a default value is used.
%  When the [D]-input parameter is not the last used in the call, it must be
%  given the value [], i.e. an empty matrix.
%  ... = There can be more parameters. They are explained under respective
%  metod or choice.
%
%References:
%  [1]: Bj鰎klund S.: "DBT, A MATLAB Toolbox for Radar Signal Processing.
%    Reference Guide", FOA-D--9x-00xxx-408--SE, To be published.
%
%See Also:
%  


% *****************************************************************************
%   *  DBT, A Matlab Toolbox for Radar Signal Processing  *
% (c) FOA 1994-2000. See the file dbtright.m for copyright notice.
%
%  Start        : 990504 Svante Bj鰎klund (svabj).
%  Latest change: $Date: 2000/10/16 15:20:53 $ $Author: svabj $.
%  $Revision: 1.4 $
% *****************************************************************************

% ----------------------------------------------------------------------- %
% Handle input parameters
% ----------------------------------------------------------------------- %

arginNo=1;
if (nargin < arginNo)
  error('DBT-Error: To few input parameters.')
end
arginNo = arginNo +1;


% ****************** Add missing input parameters ******************

if (nargin < arginNo)
  dispOpt = [];
end
arginNo = arginNo +1;
if (nargin < arginNo)
  noSrc = [];
end
arginNo = arginNo +1;


% ****************** Default values ******************

if isempty(dispOpt)
  dispOpt = '-';
end%if
if isempty(noSrc)
  noSrc = [];
end%if


% ****************** Error check input parameters ******************

chkdtype(sigIn, 'RxRadarSigT','RxCorrMatT')


% ----------------------------------------------------------------------- %
% Do the work.
% ----------------------------------------------------------------------- %


if (strcmp(sigIn.dataType,'RxCompSigT') | ...
    strcmp(sigIn.dataType,'RxRadarSigT'))

  sizeSpec = sizem(sigIn.signals);
  noPulses = sizeSpec(1);	
  noRanges = sizeSpec(2);
  noChannels = sizeSpec(3);
  noExtras = sizeSpec(4);
  noCPIs   = sizeSpec(5);
  noTrials = sizeSpec(6);

  trialLoop = 1;
  cpiLoop = 1;
  extraLoop = 1;
  rangeLoop = 1;

  sigMat = getm3(sigIn.signals, 3, [], ':',rangeLoop, ':', ...
    extraLoop, cpiLoop, trialLoop);
  corrMatMx = (1/noPulses) * sigMat*sigMat';
    % Estimate spatial correlation matrix. Use all pulses as samples.

elseif (strcmp(sigIn.dataType,'RxCorrMatT'))

  sizeSpec = sizem(sigIn.corrMat);
  noChannels = sizeSpec(1);
  %noPulses = 1;	
    % Can only store correlation matrix for a single pulse in RxCorrMatT data 
    % type.
  %noRanges = sizeSpec(3);
  %noExtras = sizeSpec(4);
  %noCPIs   = sizeSpec(5);
  %noTrials = 1;
    % Can only store correlation matrix for a single trial in RxCorrMatT data 
    % type.

  %trialLoop = 1;
  cpiLoop = 1;
  extraLoop = 1;
  rangeLoop = 1;

  corrMatMx = sigIn.corrMat(:,:,rangeLoop, extraLoop, cpiLoop);
else
  error('DBT-Error: Illegal datatype of input parameter "inData".')
end%if

if isempty(noSrc)
  noSrc = noChannels-1;
    % Default value: use only the smallest eigenvalue.
end%if

%eigVals = (flipud(sort(abs(eig(corrMatMx)))));
[U,S,V] = svd(corrMatMx);
eigVals = diag(S);
  % Calculate eigenvalues of the spatial correlation matrix.
noisePower = mean(eigVals(noSrc+1:noChannels));
  % Choose the smallest eigenvalue as an estimate of the noise power.


% ----------------------------------------------------------------------- %
% Output.
% ----------------------------------------------------------------------- %

% ****************** Output on screen ******************

if ((((nargout > 0) & (dispOpt == 'p')))| ((nargout == 0) & (dispOpt ~= 'n')))
  fprintf('Estimated noise power in radar signal = %g dB\n',10*log10(noisePower))
end%if


% ****************** Output parameters ******************

if (nargout > 0)
    noisePowerOut = noisePower;
end