Channel Knowledge Acquisition in Relay and Multipoint-to-Multipoint Transmission Systems

Most of the relaying strategies exploit channel state information (CSI), but there exist only a few limited works on acquisition of the required CSI. In this paper, we present general protocols and pilot designs for CSI acquisition in different types of relay systems using multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) transmission. We propose new pilot forwarding mechanisms and a related estimator for obtaining CSI of individual MIMO channels of cascaded links at the end node(s). We develop new pilot designs with low overhead for channels with different lengths. We present several CSI acquisition protocols for relay MIMO systems with time-division duplexing and frequency-division duplexing. We introduce node multiplexing, which reduces overhead and delay for pilot or CSI feedback transmissions from multiple nodes. In addition, we present similar CSI acquisition protocols for multipoint-to-multipoint systems while keeping the overhead low. Simulation results are included to demonstrate the estimation performance of our proposed designs. Discussions on several protocol options are also provided.