  Research and development on the next generation wireless systems, namely 5G,
has experienced explosive growth in recent years. In the physical layer (PHY),
the massive multiple-input-multiple-output (MIMO) technique and the use of high
GHz frequency bands are two promising trends for adoption. Millimeter-wave
(mmWave) bands such as 28 GHz, 38 GHz, 64 GHz, and 71 GHz, which were
previously considered not suitable for commercial cellular networks, will play
an important role in 5G. Currently, most 5G research deals with the algorithms
and implementations of modulation and coding schemes, new spatial signal
processing technologies, new spectrum opportunities, channel modeling, 5G proof
of concept (PoC) systems, and other system-level enabling technologies. In this
paper, we first investigate the contemporary wireless user equipment (UE)
hardware design, and unveil the critical 5G UE hardware design constraints on
circuits and systems. On top of the said investigation and design trade-off
analysis, a new, highly reconfigurable system architecture for 5G cellular user
equipment, namely distributed phased arrays based MIMO (DPA-MIMO) is proposed.
Finally, the link budget calculation and data throughput numerical results are
presented for the evaluation of the proposed architecture.
