LOS/NLOS Diagnostics by Frequency Auto-Correlation Patterns of MIMO/MISO Channel

We present a novel precoding method for NLOS channels that exploits their frequency auto-correlation patterns to balance frequency-selectivity and robustness. We partition the precoding band into two highly correlated sub-bands. This approach significantly outperforms wideband precoding at the cost of only twofold higher complexity. We establish that correlations for Line of Sight (LOS) channels decrease monotonically with increasing frequency or wavelength gap. In contrast, Non-Line-of-Sight (NLOS) channels exhibit periodic frequency correlation patterns, for which we derive approximate theoretical expressions.