A 28GHz Hybrid-Beamforming Transmitter Array Supporting Concurrent Dual Data Steams and Spatial Notch Steering for 5G MIMO

Spatial multiplexing, or multi-user MIMO, can improve the communication throughput by simultaneously supporting multiple spatially non-collocated data streams. Most multi-user MIMO TRXs at GHz are based on digital beamforming. However, as the data rate of each user approaches multi-Gb/s at mmWave, performing dynamic beamforming weights calculation in digital and high-speed digital-to-analog conversion faces a significant energy efficiency bottleneck for large-scale mmWave antenna arrays. Alternatively, hybrid beamforming can support a handful of concurrent data streams by combining analog beamforming with digital precoding. Although hybrid beamforming loses degrees-of-freedom compared to all-digital processing, it reduces digital computation complexity and the number of digital-to-analog conversion chains, resulting in greatly enhanced energy efficiency.