I. Introduction
Multi-Gbps user experienced data rate anywhere anytime is an important vision for fifth-generation (5G) and also for beyond fifth-generation (B5G) mobile communication. Promising solutions for achieving multi-Gbps data throughput for user terminals such as the smartphone and laptop computer include using the sub-6GHz MIMO operation and the millimeter-wave high-gain beamforming communication (see Fig. 1 for the mobile communication vision to achieve more than 1 Gbps data throughput anywhere anytime).