IDFT-VFDM for LTE FDD-NR SUL Co-existence

In the paper, an inverse discrete Fourier transform-based Vandermonde-subspace frequency division multiplexing (IDFT-VFDM) waveform is proposed for the new radio (NR) supplementary uplink (SUL) to share the same time and frequency resources with the frequency division duplex (FDD) based long-term evolution (LTE) network. To avoid the co-channel interference to the LTE user equipment (UE) uplink transmission, the interference channel state information (CSI) is necessary for the NR UE to design the interference-free precoder. Since the operating band used for NR SUL corresponds to LTE FDD mode, the channel reciprocity condition in the time division duplex (TDD) mode is no longer held. To deal with it, the reciprocity on the channel related parameters for each path, i.e. amplitude, initial phase, propagation distance, angle of arrival, angle of departure, is exploited to estimate the uplink CSI from the NR UE to the LTE base station (BS) via the downlink CSI. Accordingly, the uplink waveform is designed for the NR UE to guarantee the absence of interference towards the LTE BS with the knowledge of uplink CSI. Numerical results are presented to validate the accuracy of the CSI estimation and the merit of the IDFT-VFDM as a potential waveform to achieve the LTE FDD-NR SUL co-existence.