1. A receiver, comprising:an antenna, configured to receive a received signal on a downlink direction, wherein the received signal comprises at least one interfering downlink signal and a desired downlink signal; and
a detecting circuit, coupled to the antenna, configured to perform a multiuser detection (MUD) operation on the received signal on the downlink direction to generate a detected interfering signal and a detected desired signal;
wherein the desired downlink signal is transmitted by a first station, intended for the receiver, and generated according to a first modulation order;
wherein the interfering downlink signal is transmitted by a second station, intended for a second receiver other than the receiver, and generated according to a second modulation order;
wherein the detecting circuit performs the MUD operation via a searching operation over a product set of a first constellation set and a second constellation set, a first cardinality of the first constellation set is equal to the first modulation order, and a second cardinality of the second constellation set is equal to or less than the second modulation order.