Performance, Power, and Area Design Trade-offs in Millimeter-Wave Transmitter Beamforming Architectures

Millimeter wave (mmWave) communications is viewed as the key enabler of 5G cellular networks due to vast spectrum availability that could boost peak rate and capacity. Due to increased propagation loss in mmWave band, transceivers with massive antenna array are required to meet link budget, but their power consumption and cost become limiting factors for commercial systems. Radio designs based on hybrid digital and analog array architectures and the usage of radio frequency (RF) signal processing via phase shifters have emerged as potential solutions to improve radio energy efficiency and deliver performances close to conventional digital antenna arrays. In this paper, we provide an overview of the state-of-the-art mmWave massive antenna array designs and comparison among three array architectures, namely digital array, partially-connected hybrid array (sub-array), and fully-connected hybrid array. The comparison of performance, power, and area for these three architectures is performed for three typical 5G downlink use cases. This is the first study to comprehensively model and quantitatively analyze all design aspects and criteria including: 1) optimal beamforming precoder, 2) quantization accuracy in digital-to-analog converter (DAC) and phase shifters, 3) RF signal distribution losses, 4) power and area based on state-of-the-art mmWave circuits including high-speed DACs, mixers, phase shifters, and power amplifiers. The analysis shows that the hybrid architecture provides marginal, if any, benefits over the digital array. It also reveals that sub-array architecture suffers from reduced beamforming gain due to array partitioning, which has to be compensated with additional transmission power and signal processing. Fully-connected hybrid architecture is limited by significant RF signal distribution loss and corresponding cost of RF amplifiers needed to compensate this loss.