A base station initializes pseudo-random sequence generators on which wireless devices base generation of uplink reference signals. The base station determines a first sequence from a first subset of possible initialization sequences for a sequence generator of a first device, and determines a second sequence from a second subset of possible initialization sequences for a sequence generator of a second device. The range of this second subset spans at least the range of the first subset. The base station further encodes the first sequence as a first set of two or more parameters, and encodes the second sequence as a second set of one or more parameters. This second set includes at least one parameter not included in the first set, and comprises fewer bits than the first set. The base station initializes the sequence generators by transmitting the first and second sets of parameters to the devices.