User restriction scheme for feedback reduction of unitary matrix based SDMA

With the quantized channel state information (CSI), space division multiple access (SDMA) can extract the multiplexing gain under the limited feedback burden. However, huge signaling burden of feedback can still suffer SDMA system because the total feedback data of SDMA is linearly dependent on the number of users. Hence, we propose the user restriction scheme to control the feedback load. In this scheme, the cut-off level, which restricts the feedbacks of poor conditioned users, is suggested for the reduction of the feedback burden without the performance loss. From simulation results, then, we show that the proposed feedback scheme can achieve not only the sum-rate gain but also the reasonable feedback reduction.