Distributed Transmit Beamforming Algorithms for Unsynchronized OFDM Systems With Timing Offset
Po-Hsun Hu, Po‐Hsuan Tseng, Yi-You Guo, Chih-Chia Wei · IEEE Communications Letters · 2016
Transmit beamforming is a promising technique to enhance the coverage and signal quality for the edge user. However, the synchronization between the collaborative transmission points (TPs) is crucial for the beamforming, e.g., the timing offset (TO) and the different travel distances between TPs limit the achievable gain. In this letter, we design and implement the distributed beamforming by considering the unsynchronized multi-carrier system under frequency selective fading. The proposed distributed beamforming with K-subcarrier feedback scheme feedbacks the indicator of the gain from the user equipment to the TPs for the phase adjustment. In the proposed distributed beamforming with timing estimation feedback, the transmission of TP is enabled sequentially, where the TO is estimated between the newly enabled TP and the existing TPs. Implementation using the software-defined radio platform validates that the proposed algorithms approach the coherent beamforming gain.