Bi-directional Signaling for Dynamic TDD with Decentralized Beamforming

This paper introduces a novel bi-directional signaling scheme for decentralized beamformer design to maximize the weighted sum rate (WSR) of multi-cell multi-user multiple-input multiple-output dynamic time division duplexing (TDD) system. In particular, the base stations are assumed to be either in uplink or downlink state based on the instantaneous traffic demand. The WSR maximization problem is solved via the corresponding weighted sum mean-squared error (MSE) minimization problem. An iterative algorithm is proposed with the bi-directional signaling embedded into the TDD frame structure. A detailed signaling architecture is proposed to facilitate channel estimation, exchanging the user beamformers and the user MSE weight matrices among the coordinating nodes. The proposed coordinated system is compared with the uncoordinated system while taking into account the overhead originated from bi-directional signaling. Finally, a periodic beamformer re-initialization strategy is introduced, which enhances the beamformer convergence rate and the system performance in a time-correlated fading environment. The proposed coordinated system provides significant performance gain in an interference limited environment.