Hybrid analog-digital beamforming is a well-known cost-efficient signal processing method for massive MIMO systems. In this paper, we propose a hybrid beamforming massive MIMO system based on Rotman lens analog beamforming with beam selection and digital beamforming. Rotman lens is a true-time delay analog beamforming network supporting wide bandwidth signals, which is thus more attractive than the analog beamforming networks based on traditional narrow-band phase shifters. Hence, the performance of the proposed system is investigated and verified experimentally. In particular, we design and fabricate a sample of Rotman lens operating in 5 GHz band, whose measured performance agrees well with the computer simulation. To optimize our hybrid beamforming system in terms of error-rate performance, a low-complexity greedy beam selection algorithm is proposed. Our measurement and simulation results on the error-rate performance show that the hybrid beamforming system based on Rotman lens has a wide bandwidth and exhibits superior performance over the small-scale MIMO system under the same number of RF transceivers. |
