Methods and measurements of channel phase difference in 2×2 microwave LOS-MIMO systems

Two channel phase measurement methods of microwave Line-of-Sight Multi-Input Multi-Output (LOS-MIMO) systems are investigated. The main focus of the measurements is the MIMO phase difference which is a practically useful metric to assess LOS-MIMO channel condition and system performance. The MIMO phase difference is mainly determined by antenna positions, ground effects and atmospheric variations. The relation between antenna positions and channel condition was already addressed in a number of earlier works, while the atmospheric impact and the resulting link availability are rarely studied. In order to get insights into the phase variation of LOS-MIMO channels, we have performed measurements in order to study open-air performance of LOS-MIMO systems. Two phase measurement methods, one DSP-based approach and one sinusoidaltone-based analog technique, are developed and verified in two outdoor test links. The measurements from both methods are in good agreement with the theoretical calculation based on the antenna positions. The on-going long-term measurements will be used in the development of an availability model for LOS-MIMO systems.