# Comparative Analysis of Data Detection Techniques for 5G Massive MIMO Systems
## 1 Introduction  
In the past three decades, a rapid data traffic growth has been witnessed where the average wireless transmission rate has been doubled every 18 months. It has grown more than eight-fold between 2015 and 2020 and is expected to grow more than twenty-fold by 2022 [1]. Nowadays, the fifth-generation (5G) wireless communication system is being deployed worldwide by several mobile carriers to achieve a high data rate and a satisfactory quality of services (QoS) [2]. Figure 1 illustrates the deployment map of commercial 5G networks worldwide. One of the key target applications/scenarios of the 5G and beyond 5G (B5G) is the massive machine-type communications (mMTC) where a large number of sensor-like devices are employed and produce a choppy traffic [4, 5, 6]. The sub-6 GHz will continue the spine of future 5G wireless networks and the B5G as well. To achieve a high data rate (up to 20 Gbps), high spectral efficiency (100 bps/Hz), and high mobility (up to 1000 km/h), several technologies are considered as the backbone of the 5G networks, such as the massive multiple-input multiple-output (MIMO), millimeter wave (mmWave) [7, 8], the internet of things (IoT) [9], ultra dense networks (UDNs), visible light communications (VLC), the optical wireless communications (OWC), and the device to device (D2D) communications [10]. The IoT connects billions of sensors, devices, and machines to each other, and they exchange data among themselves. It includes countless physical components embedded with sensors, actuators, and radio frequency identification (RFID) tags and enables their cooperation and data exchange through IoT protocols [11]. D2D communication is an emerging technology to relieve the congestion in communication networks. It reduces the latency between users and hence, boost the reliability of the communication link. It facilitates data exchange among devices without the base station (BS) or access point where data can be transferred directly among connected devices without interaction with external devices. For instance, the D2D communication is considered in the third generation partnership project (3 GPP) standards to enhance the network's connectivity. Due to a huge number of connected devices and data exchange, the demand for radio spectrum is ever-increasing. The spectrum sharing (SS) is the significant technology to enhance the spectrum utilization efficiency [12]. In addition, OWC technologies can handle the spectrum crisis. For instance, visible light communication (VLC) technology can achieve a fast speed, unregulated bandwidth, high security, and high data rate communication for domestic applications [13]. The UDNs approach can coordinate the deployment of a dense small cell with very high traffic intensity. It is needed to distinguished advantages on escalating the spectrum reuse and lessening the path loss. It improves the capacity crunch and coverage. To acquire a huge bandwidth, and thus, higher data rates (Gigabits\(\backslash\) second), the mmWave spectrum is exploited. In addition, a highly directive radiation beam is required to maximize the transfer of energy to the desired user [14]. Massive MIMO is one of the crucial and mature technologies in the 5G wireless communications system both for downlink (DL) and uplink (UL) [15]. In massive MIMO, a massive number of antennas at the base station (BS) is deployed to avail simultaneously many single antenna users. Massive MIMO improves the capacity, the throughput, the reliability, the diversity gain, the performance gain, and the spectral efficiency [16]. In practice, the bottleneck in obtaining the full advantage of the massive MIMO technology is utilizing an efficient precoder, efficient detector, and accurate channel estimation. However, the BS infrastructure with a large number of antennas brings a high pressure to signal processing in terms of a high performance and a low number of computations. An accurate and instantaneous estimation of the channel state  
Figure 1: Deployment map of 5G networks [3].