## 5 Massive MIMO
The two different SNR levels yield essentially similar performance as evident in [132]. Therefore, SE can be increased by increasing the number of antenna elements because of increased data rates to the subscribers, relatively low cost to the network operators, coverage improvement, and increased service reliability [52]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sr. No.** & **Characteristics** & **Reference** \\ \hline
1 & Increased Throughput & [133] \\
2 & Reduced Radiated Power & [134] \\
3 & Unlimited Capacity & [135] \\
4 & Hardware Efficiency & [136] \\
5 & Energy Efficiency & [137] \\
6 & Multi-user Gain & [138] \\
7 & Enhanced Antenna Design & [139] \\
8 & No Cost for Extra Site & [108] \\
9 & Single-carrier Transmission & [140] \\
10 & Enhanced Spectral Efficiency & [141] \\
11 & Highly Secure & [142] \\
12 & Low Latency & [16] \\
13 & Anti-jamming & [143] \\
14 & Robust & [144] \\
15 & Enhanced QoS & [145] \\
16 & Reliability & [146] \\
17 & Omni-directional & [147] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Features of mMIMO on other key enabling techniques. As the array gain is not noise-limited and constructs the SE interference-limited, it demonstrates that Massive MIMO works equally fine at low and high SNR's. The second observation is that dissimilar pilot reuse factors are required at dissimilar customer loads (i.e., No. of subscribers \(K\)). The pilot reuse of \(f=3\) is required at less load while \(f=1\) is desired to minimize the Prelog factor (\(1-\mathrm{f}K/\tau_{c}\)) when the value of \(K\) is very large. By choosing the appropriate f, mMIMO can offer a high SE above an extensive range of various customers. The mMIMO delivers stable SE for any \(K>10\) and does not require complex scheduling as every active subscriber can essentially be served at the same time in each coherence interval or a minimum of \(\tau_{c}\) /2 subscribers, resulting in half of the coherence interval for data, which is normally greater than a hundred; the high amount of SE is then shared among all the subscribers. The significant design parameter in mMIMO is a pilot reuse factor which depends on the user load, total number of BS antennas, and propagation environment. In 3 GPP Release 18, the evolution of MIMO will continue. During the commercial deployment, significant performance loss due to outdated channel state information (CSI) by UE has been investigated with moderate or high mobility in multi-user MIMO (MU-MIMO) scenarios. To increase the performance of medium or high-mobility UE will be explored for potential CSI enhancements [32]. It is also observed that a suitable trade-off between SE and energy efficiency (EE) has an important impact on the 5G network and Beyond 5G. Hence, a balance between SE and EE is urgently needed. Also, effective algorithms need to be proposed to achieve a satisfactory trade-off. The SE in mMIMO can significantly be increased by the following methods:  
* By enhancing transmit power. * By utilizing the uplink and downlink space division multiple access (SDMA) techniques. * By acquiring an array gain. * By obtaining channel state information (CSI). Therefore, mMIMO is considered the ultimate solution for high data rate, channel capacity, and spectrum efficiency in 5G and B5G.