Performance Analysis of TDD Multicell Massive MIMO Systems with Non-Orthogonal Pilots and Hardware Imperfections in Rician Fading Channels

The performance of a time-division duplex (TDD) multicell massive MIMO ( $\mathrm{M}^2$ -MIMO) system with non-orthogonal pilots (Non-OPs) for channel estimation (CE) and hardware imperfections (HWIs), i.e., low-precision ADCs/DACs at the base station (BS) and non-ideally operating user equipment (UE) distorted by RF chain impairments (RF-CIs), is analyzed and evaluated. Assuming that this communication system operates in a Rician fading channel, firstly, the minimum mean square error (MMSE) CE complexity for both Non-OPs and orthogonal pilots (OPs) are derived and compared. It is also shown that the variance of the MMSE CE error with Non-OPs can be approximated as a linear fraction. Based on this CE analysis, the uplink (UL) and downlink (DL) spectral efficiency (SE) performances with ideal and non-ideal channel state information (CSI) are derived. Furthermore, the UL-SE performances for both Non-OPs and OPs are compared to show the advantage of using Non-OPs for applications which have very high connectivity requirements. The power scaling law is also used to obtain additional insights on how these HWIs affect the overall $\mathrm{M}^2$ -MIMO SE performance. In order to balance the total BS circuitry power consumption against UL-SE, the tradeoff between UL energy efficiency (EE) and UL-SE has been investigated by analyzing the performance of several receive detection strategies as a function of the employed ADC quantization bits (Q-bits). Moreover, the optimal ADC/DAC Q-bit region which maximizes the DL-EE is identified. Various performance evaluation results obtained by means of computer simulations have verified the analysis and validated the accuracy of the equivalent theoretical performance evaluation results.