Method of joint clustering and precoding and base station using the same

A base station, adapted to a NOMA system, and comprising:

• a transceiver circuit, configured to transmit messages to at least four user equipments;
• a storage circuit, storing a plurality of modules;
• and
• a processing circuit, coupled to the storage circuit and the transceiver circuit and configured to access and execute the modules stored in the storage circuit, and the modules comprising:
• a user configuration module, dividing the at least four user equipments into a first cluster and a second cluster each consisting of two user equipments;
• a signal generation module, generating a first cluster signal to be transmitted to the first cluster and generating a second cluster signal to be transmitted to the second cluster;
• a precoder construction module, establishing a first precoding set and a second precoding set for the first cluster and the second cluster, respectively, by using channel state information between the base station and the at least four user equipments;
• a precoder selection module, selecting a first precoder from the first precoding set and selecting a second precoder from the second precoding set, wherein the second precoder aligns a first channel and a second channel between the base station and the user equipments in the first cluster to a first space, and the first precoder aligns a third channel and a fourth channel between the base station and the user equipments in the second cluster to a second space;
• a signal computation module, multiplying the first cluster signal by the first precoder to generate a first transmission signal and multiplying the second cluster signal by the second precoder to generate a second transmission signal;
• and
• a signal superposition module, superposing the first transmission signal and the second transmission signal and broadcasting a resulting signal via the transceiver circuit to the user equipments in the first cluster and the user equipments in the second cluster.