  Hybrid precoding has been recently proposed as a cost-effective transceiver
solution for millimeter wave (mm-wave) systems. While the number of radio
frequency (RF) chains has been effectively reduced in existing works, a large
number of high-precision phase shifters are still needed. Practical phase
shifters are with coarsely quantized phases, and their number should be reduced
to a minimum due to cost and power consideration. In this paper, we propose a
novel hardware-efficient implementation for hybrid precoding, called the fixed
phase shifter (FPS) implementation. It only requires a small number of phase
shifters with quantized and fixed phases. To enhance the spectral efficiency, a
switch network is put forward to provide dynamic connections from phase
shifters to antennas, which is adaptive to the channel states. An effective
alternating minimization (AltMin) algorithm is developed with closed-form
solutions in each iteration to determine the hybrid precoder and the states of
switches. Moreover, to further reduce the hardware complexity, a
group-connected mapping strategy is proposed to reduce the number of switches.
Simulation results show that the FPS fully-connected hybrid precoder achieves
higher hardware efficiency with much fewer phase shifters than existing
proposals. Furthermore, the group-connected mapping achieves a good balance
between spectral efficiency and hardware complexity.
