Hybrid precoding design in multiuser large‐scale antenna systems under correlated fading

Millimetre wave (mmWave) signal is promising for the challenge of bandwidth shortage and canmotivate the research on large‐scale antenna arrays. In this paper, the authorsinvestigate the hybrid precoding design that combines with a radio frequency(RF) precoder and a digital precoder for multi‐user multiple‐input single‐output(MU‐MISO) systems with large‐scale antenna arrays. In practical large‐scaleantenna array systems, the small antenna spacing and the properties of ascattering environment can create a correlation between channel coefficients forseparated receive units. Such correlation prejudices the performance ofmulti‐user systems. This study proposes two approaches to reduce the channelcorrelation by the hybrid precoding structure. The first approach selects somevectors with the smallest influence with each other from all array responsevectors to design an angular‐based RF precoder. The second approach optimisesthe singular values characteristic of the virtual channel matrix before digitalprocessing for the RF precoder. Then, the MU‐MISO baseband precoding isimplemented by reduced RF chains. Numerical results show that they havedifferent performance depending on the environment. The first can achieve betterperformance when the channel correlation is not too high, while the second ismore effective when the channel realisation is terribly ill‐conditioned, especially for higher signal‐noise ratio (SNR).