Optimizing Resource Allocation of MIMO-OFDM in 4G and Beyond Systems

The blend of Multiple-Input-Multiple-Output (MIMO) and Orthogonal Frequency-Division Multiplexing (OFDM) provides a formidable air interface for fourth-generation (4G) technology. In beyond 4G standards, the derivative technologies of OFDM along with MIMO are poised to function as the air interface. The task of optimizing the performance metrics for resource allocation in MIMO-OFDM is a crucial aspect in 4G systems like Long Term Evolution (LTE) or LTE Advanced (LTE-A). As the evolution of LTE-Advanced continues and opens the vistas to fifth-generation (5G) standard, several performance metrics need to be optimized. The prime metrics which characterize a wireless system are the ergodic capacity and Spectral Efficiency (SE) of the system. There exists a precarious trade-off between SE and Energy Efficiency (EE) which needs to be judiciously balanced. Other aspects of resource optimization include enhancement of the throughput at the user end, reduction of cost per bit. This paper explores the critical aspects of potential enhancement and discusses ways to optimize resource allocation. Specific attention is given to the provisioning of the Cyclic Prefix (CP) in OFDM and use of Multiuser MIMO (MU-MIMO). Although CP is an overhead, but it is required to overcome the effects of Inter-Symbol Interference (ISI). However, adaptive CP length adjustment can improve the spectral efficiency. It is demonstrated that MU-MIMO yields a higher energy efficiency as compared to point-to-point MIMO. Therefore, MU-MIMO is ideally suited to yield a higher throughput in 4G and beyond systems.