function r = rxFilter(y, rolloff, span, sps)
  %% Receiver matched (root raised cosine) filter.
  %% Inputs:
  %%  - y: received waveform
  %%  - rolloff: rolloff factor in root raised cosine filter.
  %%  - span: filter span (number of symbols)
  %%  - sps: samples per symbol
  %% Output:
  %%  - r: filtered signal (energy not normalized),
  %%       normalize and then sample.
  rxfilter = comm.RaisedCosineReceiveFilter...
                 ('Shape', 'Square root', ...
                  'RolloffFactor', rolloff, ...
                  'FilterSpanInSymbols', span, ...
                  'InputSamplesPerSymbol', sps, ...
                  'DecimationFactor', 4, ...
                  'DecimationOffset', mod(span+1, 4));

  coef = coeffs(rxfilter);
  filter_fft = fft(coef.Numerator, length(y));
  y_fft = fft(y);

  rs = ifft(y_fft .* filter_fft.');

  %% re-order signal due to circular conv
  l = (length(coef.Numerator) - 1) / 2;
  rr = [rs(l:end); rs(1:l-1)];

  r = downsample(rr, 4, 3);
end