## 1 Introduction  
A challenging task in the design and implementation of next generation broadband wireless networks is data rate maximization for all active users, under limited bandwidth constraints. To this end, several approaches in literature have been proposed, such as the deployment of multiple input multiple output (MIMO) architecture at both ends of the wireless orientation [1]. In this case, two operational modes can be supported: diversity combining (DC), where the same information is sent and received from all antennas of the MIMO orientation, as well as spatial multiplexing (SM), where individual data streams are sent and received from the various modes of the MIMO link [2]. In DC, the mean bit error rate (BER) is improved, as outage probability is minimized, since information is sent and received from all the antennas of the MIMO configuration. In SM, transmission rates can be maximized, at the cost of increased reception complexity, since the diversity order of the system is reduced. However, in realistic wireless orientations, actual performance improvement from the deployment of MIMO architecture may be significantly different from the theoretically expected one, due to multiple access interference (MAI) [3]. In this context, various studies in recent literature have focused on estimating performance metrics in MIMO orientations. In Reference [3], the authors have derived the outage probability and capacity of cellular MIMO systems with SM and linear receivers, using the code division multiple access (CDMA) physical layer protocol. As results indicate, capacity can be severely affected in the presence of multiple interferences. In Reference [4], a CDMA network is taken into account as in Reference [3], where BER is evaluated in a Nakagami-m fading channel, considering multiple antennas at the receiver side. In Reference [5], performance metrics are presented comparing the outage probability and transmission rate of DC and SM, including a use case with the Orthogonal Frequency Division Multiplexing (OFDM) protocol. According to the presented results, the increase in the available degrees of freedom offered by SM schemes can be beneficial for the overall performance of the wireless orientation, provided that channel coding and other key features are adequately modelled. In Reference [6], an interference scenario of a heterogeneous network has been considered, where SM interferes with spatial modulation. As results indicate, in strong SM interference scenarios, significant performance degradation may occur. In Reference [7], BER is derived for massive MIMO systems, using the orthogonal frequency division multiplexing (OFDM) physical layer protocol. In this context, a reduced complexity approximation is introduced, using [PERSON]'s interpolation with different polynomial orders for log-likelihood ratio calculations. In Reference [8], the probability of error for a space-time spreading scheme in the CDMA system operating in Nakagami-m fast-fading channels using a decorrelator detector and BPSK modulation has been derived, for MIMO systems with two transmit and \(L\) receive antennas. In Reference [9], BER of MIMO-OFDM due to the frequency offset and channel estimation errors has been analyzed. The BER expressions for no combining, equal gain combining (EGC) and maximal ratio combining (MRC) were derived. Intercarrier interference (ICI) and interantenna interference (IAI) due to the residual frequency offsets were analyzed, and the average signal-to-interference-and-noise ratio (SINR) was derived. In Reference [10], BER calculations for downlink multi-user MIMO systems with imperfect channel state information (CSI) are presented, considering MIMO-OFDMA and space time block coding (STBC) scenarios. Performance evaluation of massive MIMO (M-MIMO) systems (e.g., codebook design [11], implementation issues [12], etc.) is a recent challenging research field for next generation networks [13; 14].