unication. If the phased array approach is combined with digital beamforming, the phased array approach might also be feasible for non-static or quasi-static scenarios. Considering the inefficiency of mmWave amplifiers and the high insertion loss of RF phase shifters, it is more desirable to perform the phase shifting in the baseband. The power consumption associated with both cases is comparable, as long as the 572 Chapter 4 Data stream 1 RF chain Data stream 2 Digital baseband processing precoding Data stream N RF chain Phase shifter + PA Figure 4.66 Hybrid beamforming architecture. number of antennas per RF-chain remains relatively small. A significant cost reduction can be achieved by reducing the number of complete RF chains. This does also lead to lower the overall power consumption. Since the number of data converters is significantly lower than the number of antennas, there are less degrees of freedom for digital baseband proces- sing. Thus the number of simultaneously supported streams is reduced compared to digital beamforming. The resulting performance gap is expected to be relatively low in mmWave bands, which this scheme is more suitable, due to the specific channel characteristics. The high-level block diagram of a hybrid beamforming transmitter is shown in Fig. 4.66. The precoding is divided between the analog and digital domains. In theory, it is possible to assume that each amplifier is interconnected to each radiating element. In recent years, hybrid beamforming with low-resolution data conversion (digital-to-analog/ analog-to-digital) has been studied including the energy efficiency/spectral efficiency trade- off of fully connected hybrid and digital beamforming with low-resolution data converters. One of the challenges of large antenna arrays is the increasing cost and complexity of the use of many analog-to-digital and digital-to-analog converters and other RF components to drive individual elements or subarrays. Thus the feasibility study of low-resolution and in New Radio Access Physical La