4G Long Term Evolution-Advanced (LTE-A) is an enhancement of LTE which provides high peak data
rates, flexible spectrum operations, improved system capacity, large coverage and is compatible
with existing systems. Although, it inherits all features of LTE, its own unique features are carrier
aggregation, device-to-device communication, advanced antenna techniques, heterogeneous
networks (HetNets), etc. Further, 4.5G LTE-A pro and 5G aim to increase the capacity many times, support massive connections with large coverage, provide ultra-reliable and low-latency com- munications, enhance user experience, and improve various efficiency metrics (e.g., spectrum efficiency, energy efficiency).