CKM-Based Environment-Aware Pilot Reuse and Channel Estimation

This paper considers an ultra-massive machine type communications (umMTC) system, where a base station (BS) simultaneously serves an ultra large number of user equipments (UEs). To achieve low-overhead, low-latency, and high-quality communication for umMTC system, this paper considers a batch pilot reuse technique, which can mitigate pilot contamination while reducing time overhead for channel estimation. To this end, utilizing statistical channel state information (CSI) of each UE is essential. However, in umMTC systems, it is non-trivial for the BS to directly acquire these prior information. To address this issue, motivated by the concept of channel knowledge map (CKM), we propose a channel correlation map (CCM)-based environment-aware pilot reuse and channel estimation method. Specifically, with CCM, an effective uplink (UL) pilot reuse algorithm is developed, and the UL channel of each UE is estimated by the minimum mean square error (MMSE) algorithm. Simulation results show that the proposed CCM-based technique significantly outperforms the conventional techniques that rely on UE-location-grouping and spatial-angular-division. The superior performance is expected since the CCM-based technique can integrate line-of-sight (LoS) and non-line-of-sight (NLoS) path characteristics, thus providing a more comprehensive reflection of the channel features.