Channel Estimation and Hybrid Combining for mmWave: Phase Shifters or Switches?
Roi Mendez-Rial, Cristian Rusu, Ahmed Alkhateeb, Nuria Gonzalez-Prelcic, and Robert W. Heath, Jr.
to appear in Proc. of Information Theory and Applications Workshop, Feb. 2015.
Precoding/combining and large antenna arrays are
essential in millimeter wave (mmWave) systems. In traditional
MIMO systems, precoding/combining is usually done digitally
at baseband with one radio frequency (RF) chain and one
analog-to-digital converter (ADC) per antenna. The high cost
and power consumption of RF chains and ADCs at mmWave
frequencies make an all-digital processing approach prohibitive.
When only a limited number of RF chains is available, hybrid
architectures that split the precoding/combining processing into
the analog and digital domains are attractive. A previously
proposed hybrid solution employs phase shifters and mixers
in the RF precoding/combining stage. It obtains near optimal
spectral efficiencies with a reduced number of RF channels. In
this paper we propose a different hybrid architecture, which
simplifies the hardware at the receiver by replacing the phase
shifters with switches.We present a new approach for compressed
sensing based channel estimation for the hybrid architectures.
Given the channel estimate, we propose a novel algorihtm that
jointly designs the antenna subsets selected and the baseband
combining. Using power consumption calculations and achievable
rates, we compare the performance of hybrid combining with
antenna switching and phase shifting, showing that antenna
selection is preferred in a range of operating conditions.
Paper is available here.