An uplink subsystem for use in an illumination system arranged for optical communication, the uplink subsystem comprising: a group of luminaires (2a, 2b, 2c); a group of sensors (3a, 3b, 3c) each for sampling a respective instance of an uplink signal transmitted wirelessly from a user device, with a different respective one of the sensors being incorporated in or co-located with each of the luminaires of said group, or the sensors being interspersed amongst the luminaires so as to serve a same region of space as illuminated by the group of luminaires; a demodulator unit; and an uplink distribution network arranged to supply the respective instance of the uplink signal from each of group of the sensors to the demodulator unit; wherein the demodulator unit comprises an adaptor arranged so as, based on a measurement of a respective received signal strength of each of the instances of the uplink signal, to apply a respective weight (a1, a2, a3) to each instance in dependence on the respective measurement of received signal strength, and to combine said instances of the uplink signal following the application of said weights, thereby producing a combined signal; and the demodulator unit further comprises a demodulator arranged to demodulate the combined signal and wherein the uplink subsystem utilizes a Time Division Multiplex Access scheme in which time-slots are assigned to individual uplink users and wherein the adaptor assigns weights on a time-slot basis based on a respective uplink user assigned to a respective time-slot and previously recorded instances of the uplink signal where said user's uplink signal was detected, such that the switching of the weights for the instances of the uplink signal are synchronized with the time-slots and the weights are adapted for expected arrival of signals from the uplink user associated with the current time-slot. a group of luminaires (2a, 2b, 2c); a group of sensors (3a, 3b, 3c) each for sampling a respective instance of an uplink signal transmitted wirelessly from a user device, with a different respective one of the sensors being incorporated in or co-located with each of the luminaires of said group, or the sensors being interspersed amongst the luminaires so as to serve a same region of space as illuminated by the group of luminaires; a demodulator unit; and an uplink distribution network arranged to supply the respective instance of the uplink signal from each of group of the sensors to the demodulator unit; wherein the demodulator unit comprises an adaptor arranged so as, based on a measurement of a respective received signal strength of each of the instances of the uplink signal, to apply a respective weight (a1, a2, a3) to each instance in dependence on the respective measurement of received signal strength, and to combine said instances of the uplink signal following the application of said weights, thereby producing a combined signal; and the demodulator unit further comprises a demodulator arranged to demodulate the combined signal and wherein the uplink subsystem utilizes a Time Division Multiplex Access scheme in which time-slots are assigned to individual uplink users and wherein the adaptor assigns weights on a time-slot basis based on a respective uplink user assigned to a respective time-slot and previously recorded instances of the uplink signal where said user's uplink signal was detected, such that the switching of the weights for the instances of the uplink signal are synchronized with the time-slots and the weights are adapted for expected arrival of signals from the uplink user associated with the current time-slot.