 Multi-user full-duplex massive MIMO designs are much more challenging due to multiple interferences, namely, due to (1) full-duplex users and relay resulting in self-loop and inter- user interferences, and (2) inter-pair interference, since multi-pair of users are communicating with each other using the same channel, among others. The next section will begin with the literature survey providing the brief overview of the state- of-the-art research on full-duplex multi-hop communication. It will subsequently discuss about the existing self-interference cancellation (active/passive) techniques, which help in bringing down the interference levels to the order of noise power and therefore making the full-duplex study feasible. This allows the device to transmit or receive on the same time/frequency resource, therefore resulting in higher data rate than half-duplex communication. Half-duplex-capable device, on the contrary, can only transmit or receive data at a given time/frequency resource. The detailed mathematical expressions will be provided. The chapter concludes with a summary of the topics covered and a roadmap for future directions. It will highlight the issues and challenges in massive MIMO full- duplex relay system, which are yet to be investigated. This will open a plethora of research problems which researchers can pursue in future. 4.3 Massive MIMO 5G aims to achieve an order of magnitude increase in throughput of the network. The throughput of a network can improve by (1) using higher spectrum resources resulting in higher bandwidth; (2) increasing the number of cells/km²; (3) increasing the transmit power; and (4) using large number of antennas at the base station. 5G uses massive MIMO technology, where the base station comprises 64-256 antennas, 4 Full-Duplex Multi-Hop Communication for Beyond 5G Single antenna Massive MIMO: Large number of antennas Fig. 4.1 (a) Single antenna and (b) massive MIMO which results in large array gain due to increase in the number of antennas, higher spatial multiplexing 