Muti-user multi-input multi-output communication system for constant modulus beamforming

PURPOSE: An MIMO(Multi-Input Multi-Output) communications system for constant coefficient beamforming is provided to calculate efficiently channel direction information and channel quality information in each of a zero-forcing mode and a PU2RC mode. CONSTITUTION: A terminal previously selected by a BS(Base Station) calculates differently expected user interference(S310). The differently expected user interference comprises expected inter-cell interference or expected internal cell interference. The terminal calculates E(SINRk) in a zero-forcing mode in consideration of the differently expected user interference(S320). The terminal calculates optimal channel direction information and channel quality information in the zero-forcing mode(S330). A user k feeds back the channel direction information and the channel quality information to the BS(S340).