Efficient Downlink Channel Reconstruction for FDD Multi-Antenna Systems

In this paper, we propose an efficient downlink channel reconstruction scheme for a frequency-division-duplex multi-antenna system by utilizing uplink channel state information combined with limited feedback. Based on the spatial reciprocity in a wireless channel, the downlink channel is reconstructed by using frequency-independent parameters. We first estimate the gains, delays, and angles during uplink sounding. The gains are then refined through downlink training and sent back to the base station (BS). With limited overhead, the refinement can substantially improve the accuracy of the downlink channel reconstruction. The BS can then reconstruct the downlink channel with the uplink-estimated delays and angles and the downlink-refined gains. We also introduce and extend the Newtonized orthogonal matching pursuit (NOMP) algorithm to detect the delays and gains in a multi-antenna multi-subcarrier condition. The results of our analysis show that the extended NOMP algorithm achieves high estimation accuracy. Simulations and over-the-air tests are performed to assess the performance of the efficient downlink channel reconstruction scheme. The results show that the reconstructed channel is close to the practical channel and that the accuracy is enhanced when the number of BS antennas increases, thereby highlighting that the promising application of the proposed scheme in large-scale antenna array systems

Efficient Downlink Channel Reconstruction for FDD Multi-Antenna Systems

In this paper, we propose a novel scheme to reconstruct the downlink channel of a frequency-division-duplex (FDD) multi-antenna system utilizing uplink channel state information (CSI) combined with limited feedback. Our finding is that spatial reciprocity holds among frequency-independent parameters, including the gain, delay and angle of each propagation path in a wireless channel. Based on this, we first introduce the Newtonized orthogonal matching pursuit (NOMP) algorithm to estimate these frequency-independent parameters during uplink sounding. The gains are then refined through downlink training and sent back to the base station (BS). With only a limited amount of overhead, the refinement is able to improve the accuracy of downlink channel reconstruction substantially. Utilizing the uplink-estimated delays and angles and the downlink-refined gains, the BS can reconstruct the downlink channel from the uplink estimation. We carry out both simulations and over-the-air tests to assess the performance of the proposed downlink channel reconstruction scheme. Results demonstrate that the proposed scheme is promising