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.
  filter = comm.RaisedCosineReceiveFilter...
                 ('Shape', 'Square root', ...
                  'RolloffFactor', rolloff, ...
                  'FilterSpanInSymbols', span, ...
                  'InputSamplesPerSymbol', sps, ...
                  'DecimationFactor', 1);

  r = filter([y; zeros(span * sps, 1)]);
  r = r(span * sps / 2 + 1 : end); % truncate filter transients
end