Massive MIMO will improve the performance of future 5G systems in terms of data rate and spectral efficiency, while accommodating a large number of users. Furthermore, it allows for 3D beamforming in order to provide more degrees of freedom and increase the number of high-throughput users. Massive MIMO is expected to provide more advantages compared to other solutions in terms of energy and spectral efficiency. This will be achieved by focusing the radiation towards the direction of the intended users, thus implementing simultaneous transmission to many users while keeping interference low. It can boost the capacity compared to a conventional antenna solution, resulting in a spectral efficiency up to 50 times greater than that provided by actual 4G technology. However, to take full advantage of this technology and to overcome the challenges of implementation in a real environment, a complicated radio system is required. The purpose of this work is to present the MIMO technology evolution and challenges in a simple introductory way and investigate potential system enhancements.

Mobility management plays an important role in heterogeneous networks (HetNets), because it helps to reduce radio link failures, handover delays, and power consumption, and enhances offloading benefits. In the present study, two cases are identified regarding mobility in HetNets. The first one is related to signaling and the second one is related to data transmission; i.e., handover and link rate adaptation. It has been shown that both processes are affected by the user mobility level and that performance deteriorates near cell edges. The aim is to optimize the user offloading to picocells depending on their estimated speeds so that overall system performance is maximized. The network-centric solution and cooperation between cells that achieve seamless handover is presented, and the impact of the performed measurements for link adaptation during motion is investigated.