Angle-threshold random beamforming scheme for multi-antenna system

Codebook-based multiple input multiple output (MIMO) beamforming can significantly improve the system spectral efficiency with limited feedback and gets widely adopted. However, this scheme has a drawback of heavy feedback load that the sum feedback rate can be a bottleneck for the communication system, especially when the number of users is large. In this paper, a new scheme using pseudo-random beamforming vectors and angle based threshold in the feedback process is proposed. In the proposed scheme, both the base-station and the users have no need to store a codebook. In each access procedure, the base-station generates a pseudo-random beamforming vector, and each user calculates the angle between the beamforming vectors and its channel state information (CSI) vector. If the angle is less than a predefined angle-threshold, the user feeds back its channel quality indicators (CQI), otherwise it keep silence. Compared with the codebook based scheme, the proposed scheme can largely reduce the sum feedback rate with negligible throughput loss. In particular, when the system has a constraint on the total sum feedback rate in uplink channel, the proposed scheme can increase the system throughput significantly.