A Rendez-Vous in Time: Frequency-Domain Precoding for LoS Alignment in Distributed MISO

This paper investigates the impact of Line-of-Sight (LoS) path misalignment in distributed Multiple-Input Single-Output (MISO) systems, particularly in millimeter-wave (mmWave) bands where phase synchronization and timing precision are critical. The goal is to validate a bit error rate model under practical OFDM transmission scenarios involving multiple access points communicating with user equipment. We highlight how time misalignment between LoS paths can degrade system performance and evaluate the effectiveness of various compensation strategies under such conditions. A key contribution of this work is the proposed compensation technique for LoS path misalignment. By applying a frequency-dependent linear phase shift to each subcarrier—an operation that is both low in complexity and easy to implement—we induce a circular rotation of the OFDM time-domain symbol. This rotation effectively aligns the various LoS contributions in time, as long as the path delays remain within the cyclic prefix duration. Notably, the method is fully compatible with analog beamforming architectures, which are essential in mmWave systems to reduce the number of costly RF chains. As a result, the proposed strategy enables efficient time compensation with minimal computational and hardware overhead, making it particularly attractive for distributed Multiple-Input Multiple-Output (MIMO) deployments at mmWave frequencies.