Performance of MMSE-based Symbol-level Precoding in Multi-user MISO System

The data-aided symbol-level precoding scheme has been known as a useful means of improving the system efficiency in multi-user MISO system. Even if it was mostly evaluated under the condition of an ideal channel state information (CSI), it is conjectured that its performance is critically governed by imperfect received CSI (CSIR). Furthermore, as the downlink channel can be estimated only in a block level, i.e., without tracking an effective channel on each symbol, its performance would be more seriously degraded by symbol-by-symbol channel variation. Meanwhile, we also investigate a channel coding gain for symbol-level preceding, which is not clear when the minimum distance between received signals can be increased by a nature of cumulative constructive interference gain (CCIG). The objective of this paper is to provide a complete performance comparison between the conventional block-level precoding and symbol-level precoding schemes under more realistic system assumptions.