Channel Charting Aided Pilot Allocation in Multi-Cell Massive MIMO mMTC Networks

Serving a plethora of devices in massive machinetype communications (mMTC) can rely on spatial multiplexing enabled by massive multiple-input multiple-output (mMIMO) technology. To release the full potential, accurate channel estimation is needed. Due to the large numbers of devices it necessitates pilot reuse. We propose a pilot allocation algorithm based on multi-point channel charting (CC) to mitigate inevitable pilot contamination in a multi-cell multi-sector mMTC network with spatially correlated mMIMO channels. The generated CC represents an effective interference map from channel covariance matrices to capture the degree of pilot contamination caused by sharing the same pilot sequence among multiple users. The map is then fed into a greedy algorithm that aims at optimizing the reuse pattern of orthogonal pilot sequences to minimize the performance degradation caused by pilot contamination. The proposed CC-based method is empirically shown to obtain notable gains over a reuse-factor-aware random pilot allocation, yet leaving room for further improvements.