Random unitary beamforming with partial feedback for multi-antenna downlink transmission using multiuser diversity

Multiuser diversity is well known to require a large number of users but, in this case, the requirement of a large amount of feedback (which is proportional to the number of users) may be rather critical in limiting practical applications of multiuser diversity schemes. In this paper, we study the problem of downlink transmission in multi-antenna wireless communication systems using multiuser diversity and partial user feedback. The key idea of our approach is to reduce the amount of feedback via a random unitary beamforming and sorting the users allowed for a feedback from the total number of users by means of thresholding their normalized cross-correlation with each of the beams. To address fairness issues, an equal ratio scheduling (ERC) is proposed which is applicable to scenarios with users that may have different rate requirements. Simulation results demonstrate the performance of the proposed techniques as compared to earlier multi-antenna transmission scheduling algorithms.