A device for controlling upstream transmission of bursts from optical network units (ONUs) to an optical line termination (OLT) in a passive optical network (PON), wherein the upstream transmission is organized in time intervals that form part of an upstream timeframe, includes obtain respective optical power levels received at the OLT for the ONUs; obtain respective extinction ratios at the OLT for the ONUs; obtain respective transmission wavelengths for the ONUs; distinguish pairable ONUs and non-pairable ONUs at least based on the wavelengths; pair the pairable ONUs based on the optical power levels and/or the extinction ratios to generating one or plural subsets of paired ONUs; allow paired ONUs that belong to a same subset to simultaneously transmit bursts within a time interval.