Downlink Precoding for Hybrid Fully Connected Linear Subarrays in mmWave With Rainfall Scattering and Hardware Impairments

In this treatise, we propose to design a transmit precoder at the base station (BS) for a hybrid fully connected sub-array (FCSA) architecture based on gradient projection (GP) and alternating minimization techniques. A random complex multiplicative factor comprehensively models the non-ideal nature of the power amplifier (PA), data converters (ADCs/DACs), and phase shifters (PSs) used in the transmitter radio frequency (RF) chain at the BS with the ideal mmWave channel. An effective noise term in the received signal with impairments is introduced, and the power of the same is derived. The effect of scattering of mmWave due to rainfall is taken into consideration. Two separate cases with the above-discussed impairments of (A) single user (SU) multiple-input multiple-output (MIMO) system and (B) multi-user MIMO (MU-MIMO) system are conceived. Both perfect and imperfect knowledge of the scattering parameters is considered. A linear minimum mean square error (LMMSE) channel estimation with the above impairments at the BS in the presence of rainfall scattering is performed. For both SU-MIMO and MU-MIMO systems, the spectral efficiency (SE) is evaluated for different rainfall rates at two carrier frequencies, viz. 38 GHz and 75 GHz. The channel estimate’s mean square error (MSE) for ideal and hardware impaired systems is evaluated at various rainfall rates. The performance of channel estimation is evaluated with numerical simulation.