5G Phased Array Calibration
Group Members: Jared Kantor, Chris Waldt
Advisor: Hang Liu
Sponsor: Jabil Wireless
Introduction
Antenna arrays are essential to modern wireless communication systems. Due to varying manufacturing tolerances, environmental and climate conditions, component degradation due to age, and other factors, the components in these arrays will not be able to function without both phase and amplitude calibration. Without such adjustment, there would be noticeable deviation and distortion in their output, which would lead to a decrease in signal quality and service for the end user. [cite] With mmWave implementations of 5G, these issues are intensified, with the shorter wavelength and poor propagation requiring tighter tolerances and leaving less room for error. [cite] A variety of techniques have been proposed to tackle the issue of phase calibration, including the Rotating Element Electric Field vector (REV)[cite],Multiple Element Phase Toggle (MEP)[cite] and Synthetic Array Calibration (SAC)[cite] methods. In this paper, these methods and their respective benefits and drawbacks will be analyzed, in an attempt to discern which approach, or combination of approach, is worth further investigation.
Problem Statement
Its important to get a full understanding of the difference between previous generations of wireless, for example 4G LTE, versus the newest 5G standard. Firstly, its important to make clear that there are different types of 5G, as 5G simply means 5th generation wireless, and different companies have different approaches to the what they consider this next generation. Companies such as T-Mobile advertise that they already have nationwide 5G, but the network they are promoting is specifically low-band 5G, which uses very low frequency signals to travel over extremely large distances relative to their source antenna. These signals are usually around 600 MHz. Additionally, these low band antenna systems do not utilize beamforming, and given their low frequency, the calibration process isn't as as in depth as much higher mmWave solutions. The reason why the phase calibration of higher frequency antennas gets more and more difficult is the fact that the actual length of a single period, meaning a full 360 degrees, gets smaller the higher the frequency. Looking at some numbers, a 600 MHz signal will have a period of about half a meter, but mmWave at 28.5 GHz will have a period of 10.5mm. This means that the length of one degree of a low band signal is 1.388mm, while the high-band signal is only 0.029mm, so to calibrate these high frequency antenna systems requires much greater accuracy. This is the problem we are trying to solve, with the algorithms we propose in this project, the calibration of these 5G mmWave antenna systems will become quicker, require less measurements, and less equipment then ever before, while still calibrating to the same degree of accuracy.