freqoffset.m

频率恢复的matlab实现方法

function opfilename = freqoffset(ipfilename, carroff)

%  add carrier frequency offset to a file of 'SYSCLK' sampled complex data
%
%  opfilename = freqoffset(ipfilename, carroff)
%  ipfilename: input file (*.bce), output filename is ipfilename with 'no_' prepended
%  carroff: carrier offset in Hz
%  ---------------------------------------------------------------------------

switch nargin
case 2
  % null
otherwise
  error('incorrect argument count');
end

global SYSCLK

% open files
ipfilename = setfiletype(ipfilename, 'bce');
opfilename = ['fo_' ipfilename];
opfilename = setfiletype(opfilename, 'bce');

ipfid = fopen(ipfilename, 'r');
if ipfid <= 0, error('unable to open source file'); end

opfid = fopen(opfilename, 'w');
if opfid <= 0
  fclose(ipfid);
  error('unable to open the destination file')
end

% process data in memory in BlockSize size blocks
BlockSize = 50E3;
LastPhase = 0;

%added by huanglou
[IF_PID, msg] = fopen('IF_DATA', 'w');
if (IF_PID == -1), error(msg); end

% process until run out of file data
while ~feof(ipfid)
  [data, datalen] = fread(ipfid, 2*BlockSize, 'float32');
  if datalen ~= 0
    datalen = datalen/2;
    % convert data to complex
    data =  [ 1 1i ] * reshape(data, 2, datalen);
    
    % add the frequency shift
    LoscPhase = LastPhase + 2*pi*carroff*(1:datalen)/SYSCLK;
    LastPhase = mod(LoscPhase(end),2*pi);
    data=data.*exp(j*LoscPhase);
    
    % write out the result
    count = fwrite(opfid, [real(data);imag(data)], 'float32');
    count_if= fwrite(IF_PID, [real(data);imag(data)], 'float32');
    if count ~= 2*datalen
      error('unable to write data completely');
    end
  end
end
fclose(IF_PID);
fclose(ipfid);
fclose(opfid);

%  ------------------------------------END------------------------------------