Phase Calibration of Multiple Software Defined Radio Transmitters for Beamforming in 5G Communication

Abstract

Beamforming is the key technique used in 5G communication systems for transmitting/receiving signals only in a particular direction. An accurate phase is needed to apply to the beamforming antenna array to steer the beam in a particular direction. Generally, multiple software-defined radios (SDR) are used for flexible beamforming. Whereas these multiple SDRs contain phase differences in transmitting paths due to nonlinearities in their components and the use of an individual clock and local oscillators (LO). Therefore, this paper presents the methodology to calibrate the phase differences in different transmitting paths of SDR before applying signals to the antenna elements for beamforming. This paper presents the methodology to estimate the phase offset using the cross-covariance method. A method is presented to synchronize multiple SDRs accurately. As a proof of concept, the SDR setup is built with the analog transceiver AD9371 from Analog Devices and ZC706 FPGA board from Xilinx. The measurement results with phase compensation after synchronization achieves an NMSE of around −35 dB between the signals of different transmitter paths. A 1×4 antenna array operating at 2.4 GHz has been designed in simulation, and the main beam is achieved in the desired direction after phase compensation.