Due to the rapid development of wireless communications, customers have increasing requirements for system capacity and spectral efficiency.
Various solutions, such as expanding the system bandwidth and increasing the modulation order have emerged. However, expanding the system bandwidth only increases system capacity without effectively increasing the spectral efficiency ,and increasing the modulation order increases the spectral efficiency only to a limited extent because the modulation order can hardly be doubled.
-Multiple-input multiple output(MIMO), in contrast , improves spectral efficiency several folds .MIMO is an extension of single-input single-output(SISO).
MIMO uses multiple antennas at the transmitter or receiver in combination with several signal processing techniques. MIMO improves radio link reliability and signal quality ,which further help sincrease system capacity, coverage, and user rate , and ultimately improve user experience.
-Massive MIMO achieves beamforming and multi-layer multi-subscriber resource multiplexing , greatly increasing system capacity and 3D coverage.